ChemWiki - User contributions [en]

Rep:Title=Mod:eunicemoon316

2018-05-18T16:55:42Z

Em316: /* Method: B3LYP Basis set: 6-21G(d,p) */

==BH3==

====Method: B3LYP Basis set: 3-21G====

[[File:Em316 bh3 opt.PNG]]

[[Media:EM316 BH3 OPT.LOG| EM316 BH3 OPT.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000217 0.000450 YES
RMS Force 0.000105 0.000300 YES
Maximum Displacement 0.000900 0.001800 YES
RMS Displacement 0.000441 0.001200 YES </pre>

====Method: B3LYP Basis set: 6-21G(d,p)====

[[File:Em316 bh3 sym opt 6 31G.PNG]]

[[Media:EM316 BH3 SYM OPT6 31G.LOG| EM316 BH3 SYM OPT6 31G.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000039 0.000450 YES
RMS Force 0.000025 0.000300 YES
Maximum Displacement 0.000153 0.001800 YES
RMS Displacement 0.000100 0.001200 YES </pre>

The frequencies below are the ones recalculated with the right symmetry

<pre> Low frequencies --- -19.6657 -16.7777 -16.7646 -0.0054 0.2513 0.6612
Low frequencies --- 1162.8624 1213.0925 1213.0952 </pre>

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 BH3 SYM OPT6 31G.LOG</uploadedFileContents>
</jmolApplet></jmol>

{| class="wikitable"
|+
|-
|wavenumber (cm-1 || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1163
|93
|A2
|yes
|out-of-plane bend
|-
|1213
|14
|E
|very slight
|bend
|-
|1213
|14
|E
|very slight
|bend
|-
|2583
|0
|A1
|no
|symmetric stretch
|-
|2716
|126
|E
|Yes
|asymmetric stretch
|-
|2716
|126
|E
|Yes
|asymmetric stretch
|}

[[File:Em316 bh3 IR spectrum.PNG]]

In the frequency table, there are 4 different frequencies observed: 1163, 1213, 2583 and 2716 cm-1 but in the IR spectrum there are only 3 peaks. These peaks correspond to 1163, 1213 and 2716 cm-1. The 2583cm-1 frequency IR inactive as it's a symmetric stretch and there's no change in dipole.

====MO diagram of BH3====

[[File:Em316 MO diagram complete.PNG|thumb|center|500px|MO diagram of BH3<ref>MO course handout, Trisha Hunt, 2017</ref>]]

* Are there any significant differences between the real and LCAO MOs?
There isn't mich differenced in the bonding orbital a'1, e' and non-bonding a"2 MOs. But the predicted MO of of antibonding orbital a'1 is differenct from the calculated orbital.

* What does this say about the accuracy and usefulness of qualitative MO theory?
The qualitative MO theory can predict the bonding and non-bonding orbitals accurately but anti-bonding MO may not be accurate.

==NH3==

===Method: B3LYP Basis set: 3-21G===
[[File:Nh3 first opt.PNG]]

[[Media:EM316 NH3 MOREOPT.LOG| NH3 3_21G OPT.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000057 0.000450 YES
RMS Force 0.000038 0.000300 YES
Maximum Displacement 0.000145 0.001800 YES
RMS Displacement 0.000096 0.001200 YES
Predicted change in Energy=-1.132410D-08 </pre>

===Method: B3LYP Basis set: 6-21G(d,p)===

[[File:Nh3 first opt 6-31G.PNG]]

[[Media:EM316 NH3 OPT 6 31G.LOG| EM316 NH3 OPT 6 31G.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000060 0.000450 YES
RMS Force 0.000040 0.000300 YES
Maximum Displacement 0.000369 0.001800 YES
RMS Displacement 0.000162 0.001200 YES
Predicted change in Energy=-2.259205D-08 </pre>

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 NH3 OPT 6 31G.LOG</uploadedFileContents>
</jmolApplet></jmol>

'''Frequency Analysis'''
<pre>
Low frequencies --- -30.2442 -30.2441 -27.9027 -0.0013 0.0008 0.0030
Low frequencies --- 1088.3853 1693.7756 1693.7756</pre>

[[File:Em316 Ir spectrum of nh3.PNG]]

{| class="wikitable"
|+
|-
|wavenumber (cm-1 || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1088
|146
|A1
|yes
|out-of-plane bend
|-
|1694
|14
|E
|very slight
|bend
|-
|1694
|14
|E
|very slight
|bend
|-
|3462
|1
|A1
|no
|symmetric stretch
|-
|3591
|0
|E
|Yes
|asymmetric stretch
|-
|3591
|0
|E
|Yes
|asymmetric stretch
|}

==NH3BH3==

===Method: B3LYP Basis set: 6-21G(d,p)===

[[File:Em316 nh3bh3 6 21G OPT.PNG]]

[[Media:NH3BH3 6 21G OPT FREQ.LOG| NH3BH3 6 21G OPT FREQ.LOG]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>NH3BH3 6 21G OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

<pre> Item Value Threshold Converged?
Maximum Force 0.000131 0.000450 YES
RMS Force 0.000037 0.000300 YES
Maximum Displacement 0.000654 0.001800 YES
RMS Displacement 0.000179 0.001200 YES
Predicted change in Energy=-1.115346D-07 </pre>

'''Vibrational spectrum'''
{| class="wikitable"
|+
|-
|wavenumber (cm-1 || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|264
|0
|A2
|no
|N-B rotation
|-
|634
|14
|E
|slight
|N-B stretching
|-
|639
|4
|E
|very slight
|N-B twsting
|-
|639
|4
|A1
|very slight
|N-B rocking
|-
|1069
|41
|E
|Yes
|N-B twsting
|-
|1069
|41
|E
|Yes
|N-B rocking
|-
|1196
|108
|E
|Yes
|B-H out-of-plane bend
|-
|1204
|3
|E
|very slight
|N-H bend
|-
|1204
|3
|E
|very slight
|N-H bend
|-
|1330
|113
|E
|Yes
|N-H out-of-plane bend
|-
|1676
|28
|E
|Yes
|N-H bend
|-
|1676
|28
|E
|Yes
|N-H bend
|-
|2472
|67
|E
|Yes
|B-H symmetric stretch
|-
|2532
|231
|E
|Yes
|B-H asymmetric stretch
|-
|2532
|231
|E
|Yes
|B-H asymmetric stretch
|-
|3464
|2
|E
|very slight
|N-H symmetric stretch
|-
|3580
|28
|E
|Yes
|N-H asymmetric stretch
|-
|3580
|28
|E
|Yes
|N-H asymmetric stretch
|}

[[File:Em316 bh3 IR spectrum.PNG]]

===Energy Calculation===
E(NH3)= -26.46226 a.u.
E(BH3)= -56.55776 a.u.
E(NH3BH3)= -83.22468 a.u.

ΔE=E(NH3BH3)-[E(NH3)+E(BH3)]
=-83.22468 -(-26.46226 + -56.55776)
=-0.20466 a.u.
=-537.33483 kJ/mol

The bond dissociation energy has a negative value as it's an exothermic reaction. The calculated value is negative which fits in with the theory. Also the bond strength varies between 3-1000 kl/mol therefore -537 kJ/mol is a sensible value for a bond dissociation energy.

* Based on your energy calculation is the B-N dative bond weak, medium or strong? What comparison have you made to come to this conclusion?
The energy of B-N bond is medium. One of the strong bonds NΞN dissociation energy is 945 kJ/mol and C-O bond's dissociation energy is 1077 kJ/mol. Weak bonds such as Br-Br has a bond dissociation energy value of 192 kJ/mol.<ref>https://en.wikipedia.org/wiki/Bond-dissociation_energy</ref> B-N bond has a dissociation energy value in between the strong and weak bond dissociation energy, therefore, B-N bond energy is medium.

==BBr3==
====Method: B3LYP Basis set: 6-21G GEN====

[[File:Bbr3 summary em316.PNG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000001 0.000450 YES
RMS Force 0.000001 0.000300 YES
Maximum Displacement 0.000006 0.001800 YES
RMS Displacement 0.000004 0.001200 YES
Predicted change in Energy=-1.206088D-11
Optimization completed. </pre>

<pre>Low frequencies --- -0.0116 -0.0065 -0.0004 49.9506 49.9506 50.0315
Low frequencies --- 144.7606 144.7640 215.6181</pre>

[[Media:BBr3 plswork web OPt.log| BBr3 optimised.log]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>BBr3 plswork web OPt.log</uploadedFileContents>
</jmolApplet></jmol>

==Aromaticity==
===Benzene===

====Method: B3LYP Basis set: 6-21G(d,p)====

[[File:Benzene summary table.PNG]]

[[Media:EM316 BENZENE 6 21G FREQMO.LOG| EM316 BENZENE 6 21G OPT.LOG]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 BENZENE 6 21G FREQMO.LOG</uploadedFileContents>
</jmolApplet></jmol>

<pre> Item Value Threshold Converged?
Maximum Force 0.000049 0.000450 YES
RMS Force 0.000021 0.000300 YES
Maximum Displacement 0.000068 0.001800 YES
RMS Displacement 0.000030 0.001200 YES
Predicted change in Energy=-8.796913D-09 </pre>

'''Frequency Analysis'''

<pre>Low frequencies --- -11.2053 -7.2445 -7.2445 -0.0055 -0.0055 -0.0007
Low frequencies --- 414.4985 414.4985 621.0620
Diagonal vibrational polarizability:
0.2795691 0.2795903 4.1346737
Harmonic frequencies (cm**-1), IR intensities (KM/Mole), Raman scattering
activities (A**4/AMU), depolarization ratios for plane and unpolarized
incident light, reduced masses (AMU), force constants (mDyne/A),
and normal coordinates:
1 2 3
E2U E2U E2G
Frequencies -- 414.4985 414.4985 621.0620
Red. masses -- 2.9462 2.9462 6.0756
Frc consts -- 0.2982 0.2982 1.3807
IR Inten -- 0.0000 0.0000 0.0000</pre>

===Borazine===

====Method: B3LYP Basis set: 6-21G(d,p)====

[[File:Borazine results table.PNG]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 BORAZINE 6 21G FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

[[Media:EM316 BORAZINE 6 21G FREQ.LOG| EM316 BORAZINE 6 21G.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000290 0.000450 YES
RMS Force 0.000119 0.000300 YES
Maximum Displacement 0.000581 0.001800 YES
RMS Displacement 0.000278 0.001200 YES
Predicted change in Energy=-4.469792D-07 </pre>

'''Frequency Analysis'''

<pre>Low frequencies --- -14.2714 -13.9795 -10.8868 -0.0110 0.0326 0.0561
Low frequencies --- 289.1178 289.1292 404.2716
Diagonal vibrational polarizability:
7.3588310 7.3578646 14.1611762
Harmonic frequencies (cm**-1), IR intensities (KM/Mole), Raman scattering
activities (A**4/AMU), depolarization ratios for plane and unpolarized
incident light, reduced masses (AMU), force constants (mDyne/A),
and normal coordinates:
1 2 3
E" E" A2"
Frequencies -- 289.1170 289.1284 404.2716
Red. masses -- 2.9298 2.9298 1.9279
Frc consts -- 0.1443 0.1443 0.1856
IR Inten -- 0.0000 0.0000 23.7973</pre>

====Benzene and Borazine comparison====

=====Charge distribution=====
[[File:Charge comparison3 em316.PNG|500px|center]]

The charge distribution on benzene is: C= -0.084 eV, H = 0084. eV
For the Borazine: B= 0.747 eV, N= -1.102 eV, H(N-H)= 0.432 eV, H(B-H)= -0.077 eV

For benzene all the carbon molecule has a same charge; -0.084 eV. And the charge is negative as carbon is more electronegative than hydrogen thus there's more electron density on carbon than the hydrogen.

The charge differences in borazine can be explained through the same principle: nitrogen is more electronegative than both boron and hydrogen thus it has the most negative charge. Therefore the charge on hydrogen of N-H bond is slightly more positive than the hydrogen in B-H bond: the electron density on hydrogen is pulled towards the electronegative nitrogen. On the other hand, boron is less electronegative than hydrogen so B-H hydrogen has slightly negative charge.

=====Molecular Orbitals=====

{| class="wikitable"
|+
|-
|MO || Benzene || Borazine || Description
|-
|MO11
|[[File:Mo11 benzene em316.PNG|200px]]
|[[File:MO11 borazine em316.PNG|200px]]
|MO11 shows both bonding and antibonding MO for both complexes.
The benzene MO is very symmetric with 2 nodes at the centre of carbon. There are in-phase overlap(bonding) of s atomic orbitals from 4 hydrogens and p atomic orbital from the 4 carbons on the both sides. There’s anti-bonding character as there are different phase orbitals(shown as red or green) close together.
The borazine MO has the similar characteristics but it’s less symmetrical. There’s am overlap between the top nitrogen p atomic orbital and s atomic orbitals of hydrogen.
|-
|MO17
|[[File:Mo17 benzene em316.PNG|200px]]
|[[File:Mo17 borazine em316.PNG|200px]]
|MO 17 ,again, has both bonding and small antibonding characteristic for both complexes. In benzene there are pz orbital contribution from carbon and no contribution from H atoms. As can be seen from each phase of orbital completely covering the carbon ring, the pz atomic orbitals are delocalised. There’s a nodal plane along the molecule.
The borazine’s MO is similar to the benzene’s with only boron and nitrogen’s p atomic orbital contributes to MO. This MO shows pi aspect of bonding.
|-
|MO20
|[[File:Mo20 benzene em316.PNG|200px]]
|[[File:MO20 borazine em316.PNG|200px]]
|MO20 have small bonding feature from 4 atoms. Both molecules have two nodal planes: through the centre and through the bonds. Therefore this MO has more antibonding characteristic than bonding. The benzene Mo is totally symmetric whereas the borazine’s one is not: the electron density is greater on the more electronegative nitrogen.
|}

=====Aromaticity=====

MO20 for both benzene and borazine, delocalised electron density above and below the nodal plane can be observed. This relates to the pi-electron delocalisation which is a common concept of aromatic molecules.

On the other hand, just relying on the overlap of Pz AOs to account for aromaticity is not suitable. The key concept of aromaticity is the aromatic stability which is result of pi-delocalisation. However, not only pi-electron structure contributes to the stability but sigma electron structure as well. <ref>Application of AIM Parameters at Ring Critical Points for Estimation ofp-Electron Delocalization in Six-Membered Aromatic andQuasi-Aromatic Rings,Palusick,M ,Krygowski,T ,</ref>

Also there are other factors which needs to be considered for a molecule to be aromatic:
The molecule must be cyclic. The ring needs to be planar. Each atom in the ring must be sp2-hybridised. The number of pi-electrons must obey the Huckle's rule(4n+2).<ref>https://chem.libretexts.org/Textbook_Maps/Organic_Chemistry_Textbook_Maps/Map%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)/Chapter_02%3A_Introduction_to_organic_structure_and_bonding_II/2.2%3A_Molecular_orbital_theory%3A_conjugation_and_aromaticity</ref>

[[File:Frost circle em316.PNG|500px|thumb|Benzene and Borazine in the Frost Circle|center]]

In the frost circle diagram, both benzene and borazine have 6 electrons occupying all three pi MO but anti-bonding MOs are not occupied. Fully occupied bonding orbitals provide 'full shell' of electrons, which creates a similar effect to a full shell of electrons in noble gasses, thus stabilising the molecules.<ref>http://www.chemgapedia.de/vsengine/vlu/vsc/en/ch/12/oc/vlu_organik/aromaten/aromaten/aromaten_gesamt.vlu/Page/vsc/en/ch/12/oc/aromaten/aromaten/frost/frost.vscml.html</ref> Therefore, there are many factors in aromatic stability than just a delocalisation of pi electrons.

====Reference====
<references/>

Rep:Title=Mod:eunicemoon316

2018-05-18T16:54:44Z

Em316: /* Method: B3LYP Basis set: 6-21G(d,p) */

==BH3==

====Method: B3LYP Basis set: 3-21G====

[[File:Em316 bh3 opt.PNG]]

[[Media:EM316 BH3 OPT.LOG| EM316 BH3 OPT.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000217 0.000450 YES
RMS Force 0.000105 0.000300 YES
Maximum Displacement 0.000900 0.001800 YES
RMS Displacement 0.000441 0.001200 YES </pre>

====Method: B3LYP Basis set: 6-21G(d,p)====

[[File:Em316 bh3 sym opt 6 31G.PNG]]

[[Media:EM316 BH3 SYM OPT6 31G.LOG| EM316 BH3 SYM OPT6 31G.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000039 0.000450 YES
RMS Force 0.000025 0.000300 YES
Maximum Displacement 0.000153 0.001800 YES
RMS Displacement 0.000100 0.001200 YES </pre>

The frequencies below are the ones recalculated with the right symmetry

<pre> Low frequencies --- -19.6657 -16.7777 -16.7646 -0.0054 0.2513 0.6612
Low frequencies --- 1162.8624 1213.0925 1213.0952 </pre>

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 BH3 SYM OPT6 31G.LOG</uploadedFileContents>
</jmolApplet></jmol>

{| class="wikitable"
|+
|-
|wavenumber (cm-1 || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1163
|93
|A2
|yes
|out-of-plane bend
|-
|1213
|14
|E
|very slight
|bend
|-
|1213
|14
|E
|very slight
|bend
|-
|2583
|0
|A1
|no
|symmetric stretch
|-
|2716
|126
|E
|Yes
|asymmetric stretch
|-
|2716
|126
|E
|Yes
|asymmetric stretch
|}

[[File:Em316 bh3 IR spectrum.PNG]]

In the frequency table, there are 4 different frequencies observed: 1163, 1213, 2583 and 2716 cm-1 but in the IR spectrum there are only 3 peaks. These peaks correspond to 1163, 1213 and 2716 cm-1. The 2583cm-1 frequency IR inactive as it's a symmetric stretch and there's no change in dipole.

====MO diagram of BH3====

[[File:Em316 MO diagram complete.PNG|thumb|center|500px|MO diagram of BH3<ref>MO course handout, Trisha Hunt, 2017</ref>]]

* Are there any significant differences between the real and LCAO MOs?
There isn't mich differenced in the bonding orbital a'1, e' and non-bonding a"2 MOs. But the predicted MO of of antibonding orbital a'1 is differenct from the calculated orbital.

* What does this say about the accuracy and usefulness of qualitative MO theory?
The qualitative MO theory can predict the bonding and non-bonding orbitals accurately but anti-bonding MO may not be accurate.

==NH3==

===Method: B3LYP Basis set: 3-21G===
[[File:Nh3 first opt.PNG]]

[[Media:EM316 NH3 MOREOPT.LOG| NH3 3_21G OPT.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000057 0.000450 YES
RMS Force 0.000038 0.000300 YES
Maximum Displacement 0.000145 0.001800 YES
RMS Displacement 0.000096 0.001200 YES
Predicted change in Energy=-1.132410D-08 </pre>

===Method: B3LYP Basis set: 6-21G(d,p)===

[[File:Nh3 first opt 6-31G.PNG]]

[[Media:EM316 NH3 OPT 6 31G.LOG| EM316 NH3 OPT 6 31G.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000060 0.000450 YES
RMS Force 0.000040 0.000300 YES
Maximum Displacement 0.000369 0.001800 YES
RMS Displacement 0.000162 0.001200 YES
Predicted change in Energy=-2.259205D-08 </pre>

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 NH3 OPT 6 31G.LOG</uploadedFileContents>
</jmolApplet></jmol>

'''Frequency Analysis'''
<pre>
Low frequencies --- -30.2442 -30.2441 -27.9027 -0.0013 0.0008 0.0030
Low frequencies --- 1088.3853 1693.7756 1693.7756</pre>

[[File:Em316 Ir spectrum of nh3.PNG]]

{| class="wikitable"
|+
|-
|wavenumber (cm-1 || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1088
|146
|A1
|yes
|out-of-plane bend
|-
|1694
|14
|E
|very slight
|bend
|-
|1694
|14
|E
|very slight
|bend
|-
|3462
|1
|A1
|no
|symmetric stretch
|-
|3591
|0
|E
|Yes
|asymmetric stretch
|-
|3591
|0
|E
|Yes
|asymmetric stretch
|}

==NH3BH3==

===Method: B3LYP Basis set: 6-21G(d,p)===

[[File:Em316 nh3bh3 6 21G OPT.PNG]]

[[Media:EM316 NH3BH3 6 21G OPT FREQ.LOG| NH3BH3 6 21G OPT .LOG]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>NH3BH3 6 21G OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

<pre> Item Value Threshold Converged?
Maximum Force 0.000131 0.000450 YES
RMS Force 0.000037 0.000300 YES
Maximum Displacement 0.000654 0.001800 YES
RMS Displacement 0.000179 0.001200 YES
Predicted change in Energy=-1.115346D-07 </pre>

'''Vibrational spectrum'''
{| class="wikitable"
|+
|-
|wavenumber (cm-1 || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|264
|0
|A2
|no
|N-B rotation
|-
|634
|14
|E
|slight
|N-B stretching
|-
|639
|4
|E
|very slight
|N-B twsting
|-
|639
|4
|A1
|very slight
|N-B rocking
|-
|1069
|41
|E
|Yes
|N-B twsting
|-
|1069
|41
|E
|Yes
|N-B rocking
|-
|1196
|108
|E
|Yes
|B-H out-of-plane bend
|-
|1204
|3
|E
|very slight
|N-H bend
|-
|1204
|3
|E
|very slight
|N-H bend
|-
|1330
|113
|E
|Yes
|N-H out-of-plane bend
|-
|1676
|28
|E
|Yes
|N-H bend
|-
|1676
|28
|E
|Yes
|N-H bend
|-
|2472
|67
|E
|Yes
|B-H symmetric stretch
|-
|2532
|231
|E
|Yes
|B-H asymmetric stretch
|-
|2532
|231
|E
|Yes
|B-H asymmetric stretch
|-
|3464
|2
|E
|very slight
|N-H symmetric stretch
|-
|3580
|28
|E
|Yes
|N-H asymmetric stretch
|-
|3580
|28
|E
|Yes
|N-H asymmetric stretch
|}

[[File:Em316 bh3 IR spectrum.PNG]]

===Energy Calculation===
E(NH3)= -26.46226 a.u.
E(BH3)= -56.55776 a.u.
E(NH3BH3)= -83.22468 a.u.

ΔE=E(NH3BH3)-[E(NH3)+E(BH3)]
=-83.22468 -(-26.46226 + -56.55776)
=-0.20466 a.u.
=-537.33483 kJ/mol

The bond dissociation energy has a negative value as it's an exothermic reaction. The calculated value is negative which fits in with the theory. Also the bond strength varies between 3-1000 kl/mol therefore -537 kJ/mol is a sensible value for a bond dissociation energy.

* Based on your energy calculation is the B-N dative bond weak, medium or strong? What comparison have you made to come to this conclusion?
The energy of B-N bond is medium. One of the strong bonds NΞN dissociation energy is 945 kJ/mol and C-O bond's dissociation energy is 1077 kJ/mol. Weak bonds such as Br-Br has a bond dissociation energy value of 192 kJ/mol.<ref>https://en.wikipedia.org/wiki/Bond-dissociation_energy</ref> B-N bond has a dissociation energy value in between the strong and weak bond dissociation energy, therefore, B-N bond energy is medium.

==BBr3==
====Method: B3LYP Basis set: 6-21G GEN====

[[File:Bbr3 summary em316.PNG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000001 0.000450 YES
RMS Force 0.000001 0.000300 YES
Maximum Displacement 0.000006 0.001800 YES
RMS Displacement 0.000004 0.001200 YES
Predicted change in Energy=-1.206088D-11
Optimization completed. </pre>

<pre>Low frequencies --- -0.0116 -0.0065 -0.0004 49.9506 49.9506 50.0315
Low frequencies --- 144.7606 144.7640 215.6181</pre>

[[Media:BBr3 plswork web OPt.log| BBr3 optimised.log]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>BBr3 plswork web OPt.log</uploadedFileContents>
</jmolApplet></jmol>

==Aromaticity==
===Benzene===

====Method: B3LYP Basis set: 6-21G(d,p)====

[[File:Benzene summary table.PNG]]

[[Media:EM316 BENZENE 6 21G FREQMO.LOG| EM316 BENZENE 6 21G OPT.LOG]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 BENZENE 6 21G FREQMO.LOG</uploadedFileContents>
</jmolApplet></jmol>

<pre> Item Value Threshold Converged?
Maximum Force 0.000049 0.000450 YES
RMS Force 0.000021 0.000300 YES
Maximum Displacement 0.000068 0.001800 YES
RMS Displacement 0.000030 0.001200 YES
Predicted change in Energy=-8.796913D-09 </pre>

'''Frequency Analysis'''

<pre>Low frequencies --- -11.2053 -7.2445 -7.2445 -0.0055 -0.0055 -0.0007
Low frequencies --- 414.4985 414.4985 621.0620
Diagonal vibrational polarizability:
0.2795691 0.2795903 4.1346737
Harmonic frequencies (cm**-1), IR intensities (KM/Mole), Raman scattering
activities (A**4/AMU), depolarization ratios for plane and unpolarized
incident light, reduced masses (AMU), force constants (mDyne/A),
and normal coordinates:
1 2 3
E2U E2U E2G
Frequencies -- 414.4985 414.4985 621.0620
Red. masses -- 2.9462 2.9462 6.0756
Frc consts -- 0.2982 0.2982 1.3807
IR Inten -- 0.0000 0.0000 0.0000</pre>

===Borazine===

====Method: B3LYP Basis set: 6-21G(d,p)====

[[File:Borazine results table.PNG]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 BORAZINE 6 21G FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

[[Media:EM316 BORAZINE 6 21G FREQ.LOG| EM316 BORAZINE 6 21G.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000290 0.000450 YES
RMS Force 0.000119 0.000300 YES
Maximum Displacement 0.000581 0.001800 YES
RMS Displacement 0.000278 0.001200 YES
Predicted change in Energy=-4.469792D-07 </pre>

'''Frequency Analysis'''

<pre>Low frequencies --- -14.2714 -13.9795 -10.8868 -0.0110 0.0326 0.0561
Low frequencies --- 289.1178 289.1292 404.2716
Diagonal vibrational polarizability:
7.3588310 7.3578646 14.1611762
Harmonic frequencies (cm**-1), IR intensities (KM/Mole), Raman scattering
activities (A**4/AMU), depolarization ratios for plane and unpolarized
incident light, reduced masses (AMU), force constants (mDyne/A),
and normal coordinates:
1 2 3
E" E" A2"
Frequencies -- 289.1170 289.1284 404.2716
Red. masses -- 2.9298 2.9298 1.9279
Frc consts -- 0.1443 0.1443 0.1856
IR Inten -- 0.0000 0.0000 23.7973</pre>

====Benzene and Borazine comparison====

=====Charge distribution=====
[[File:Charge comparison3 em316.PNG|500px|center]]

The charge distribution on benzene is: C= -0.084 eV, H = 0084. eV
For the Borazine: B= 0.747 eV, N= -1.102 eV, H(N-H)= 0.432 eV, H(B-H)= -0.077 eV

For benzene all the carbon molecule has a same charge; -0.084 eV. And the charge is negative as carbon is more electronegative than hydrogen thus there's more electron density on carbon than the hydrogen.

The charge differences in borazine can be explained through the same principle: nitrogen is more electronegative than both boron and hydrogen thus it has the most negative charge. Therefore the charge on hydrogen of N-H bond is slightly more positive than the hydrogen in B-H bond: the electron density on hydrogen is pulled towards the electronegative nitrogen. On the other hand, boron is less electronegative than hydrogen so B-H hydrogen has slightly negative charge.

=====Molecular Orbitals=====

{| class="wikitable"
|+
|-
|MO || Benzene || Borazine || Description
|-
|MO11
|[[File:Mo11 benzene em316.PNG|200px]]
|[[File:MO11 borazine em316.PNG|200px]]
|MO11 shows both bonding and antibonding MO for both complexes.
The benzene MO is very symmetric with 2 nodes at the centre of carbon. There are in-phase overlap(bonding) of s atomic orbitals from 4 hydrogens and p atomic orbital from the 4 carbons on the both sides. There’s anti-bonding character as there are different phase orbitals(shown as red or green) close together.
The borazine MO has the similar characteristics but it’s less symmetrical. There’s am overlap between the top nitrogen p atomic orbital and s atomic orbitals of hydrogen.
|-
|MO17
|[[File:Mo17 benzene em316.PNG|200px]]
|[[File:Mo17 borazine em316.PNG|200px]]
|MO 17 ,again, has both bonding and small antibonding characteristic for both complexes. In benzene there are pz orbital contribution from carbon and no contribution from H atoms. As can be seen from each phase of orbital completely covering the carbon ring, the pz atomic orbitals are delocalised. There’s a nodal plane along the molecule.
The borazine’s MO is similar to the benzene’s with only boron and nitrogen’s p atomic orbital contributes to MO. This MO shows pi aspect of bonding.
|-
|MO20
|[[File:Mo20 benzene em316.PNG|200px]]
|[[File:MO20 borazine em316.PNG|200px]]
|MO20 have small bonding feature from 4 atoms. Both molecules have two nodal planes: through the centre and through the bonds. Therefore this MO has more antibonding characteristic than bonding. The benzene Mo is totally symmetric whereas the borazine’s one is not: the electron density is greater on the more electronegative nitrogen.
|}

=====Aromaticity=====

MO20 for both benzene and borazine, delocalised electron density above and below the nodal plane can be observed. This relates to the pi-electron delocalisation which is a common concept of aromatic molecules.

On the other hand, just relying on the overlap of Pz AOs to account for aromaticity is not suitable. The key concept of aromaticity is the aromatic stability which is result of pi-delocalisation. However, not only pi-electron structure contributes to the stability but sigma electron structure as well. <ref>Application of AIM Parameters at Ring Critical Points for Estimation ofp-Electron Delocalization in Six-Membered Aromatic andQuasi-Aromatic Rings,Palusick,M ,Krygowski,T ,</ref>

Also there are other factors which needs to be considered for a molecule to be aromatic:
The molecule must be cyclic. The ring needs to be planar. Each atom in the ring must be sp2-hybridised. The number of pi-electrons must obey the Huckle's rule(4n+2).<ref>https://chem.libretexts.org/Textbook_Maps/Organic_Chemistry_Textbook_Maps/Map%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)/Chapter_02%3A_Introduction_to_organic_structure_and_bonding_II/2.2%3A_Molecular_orbital_theory%3A_conjugation_and_aromaticity</ref>

[[File:Frost circle em316.PNG|500px|thumb|Benzene and Borazine in the Frost Circle|center]]

In the frost circle diagram, both benzene and borazine have 6 electrons occupying all three pi MO but anti-bonding MOs are not occupied. Fully occupied bonding orbitals provide 'full shell' of electrons, which creates a similar effect to a full shell of electrons in noble gasses, thus stabilising the molecules.<ref>http://www.chemgapedia.de/vsengine/vlu/vsc/en/ch/12/oc/vlu_organik/aromaten/aromaten/aromaten_gesamt.vlu/Page/vsc/en/ch/12/oc/aromaten/aromaten/frost/frost.vscml.html</ref> Therefore, there are many factors in aromatic stability than just a delocalisation of pi electrons.

====Reference====
<references/>

2018-05-18T16:41:53Z

Em316: /* Aromaticity */

==BH3==

====Method: B3LYP Basis set: 3-21G====

[[File:Em316 bh3 opt.PNG]]

[[Media:EM316 BH3 OPT.LOG| EM316 BH3 OPT.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000217 0.000450 YES
RMS Force 0.000105 0.000300 YES
Maximum Displacement 0.000900 0.001800 YES
RMS Displacement 0.000441 0.001200 YES </pre>

====Method: B3LYP Basis set: 6-21G(d,p)====

[[File:Em316 bh3 sym opt 6 31G.PNG]]

[[Media:EM316 BH3 SYM OPT6 31G.LOG| EM316 BH3 SYM OPT6 31G.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000039 0.000450 YES
RMS Force 0.000025 0.000300 YES
Maximum Displacement 0.000153 0.001800 YES
RMS Displacement 0.000100 0.001200 YES </pre>

The frequencies below are the ones recalculated with the right symmetry

<pre> Low frequencies --- -19.6657 -16.7777 -16.7646 -0.0054 0.2513 0.6612
Low frequencies --- 1162.8624 1213.0925 1213.0952 </pre>

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 BH3 SYM OPT6 31G.LOG</uploadedFileContents>
</jmolApplet></jmol>

{| class="wikitable"
|+
|-
|wavenumber (cm-1 || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1163
|93
|A2
|yes
|out-of-plane bend
|-
|1213
|14
|E
|very slight
|bend
|-
|1213
|14
|E
|very slight
|bend
|-
|2583
|0
|A1
|no
|symmetric stretch
|-
|2716
|126
|E
|Yes
|asymmetric stretch
|-
|2716
|126
|E
|Yes
|asymmetric stretch
|}

[[File:Em316 bh3 IR spectrum.PNG]]

In the frequency table, there are 4 different frequencies observed: 1163, 1213, 2583 and 2716 cm-1 but in the IR spectrum there are only 3 peaks. These peaks correspond to 1163, 1213 and 2716 cm-1. The 2583cm-1 frequency IR inactive as it's a symmetric stretch and there's no change in dipole.

====MO diagram of BH3====

[[File:Em316 MO diagram complete.PNG|thumb|center|500px|MO diagram of BH3<ref>MO course handout, Trisha Hunt, 2017</ref>]]

* Are there any significant differences between the real and LCAO MOs?
There isn't mich differenced in the bonding orbital a'1, e' and non-bonding a"2 MOs. But the predicted MO of of antibonding orbital a'1 is differenct from the calculated orbital.

* What does this say about the accuracy and usefulness of qualitative MO theory?
The qualitative MO theory can predict the bonding and non-bonding orbitals accurately but anti-bonding MO may not be accurate.

==NH3==

===Method: B3LYP Basis set: 3-21G===
[[File:Nh3 first opt.PNG]]

[[Media:EM316 NH3 MOREOPT.LOG| NH3 3_21G OPT.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000057 0.000450 YES
RMS Force 0.000038 0.000300 YES
Maximum Displacement 0.000145 0.001800 YES
RMS Displacement 0.000096 0.001200 YES
Predicted change in Energy=-1.132410D-08 </pre>

===Method: B3LYP Basis set: 6-21G(d,p)===

[[File:Nh3 first opt 6-31G.PNG]]

[[Media:EM316 NH3 OPT 6 31G.LOG| EM316 NH3 OPT 6 31G.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000060 0.000450 YES
RMS Force 0.000040 0.000300 YES
Maximum Displacement 0.000369 0.001800 YES
RMS Displacement 0.000162 0.001200 YES
Predicted change in Energy=-2.259205D-08 </pre>

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 NH3 OPT 6 31G.LOG</uploadedFileContents>
</jmolApplet></jmol>

'''Frequency Analysis'''
<pre>
Low frequencies --- -30.2442 -30.2441 -27.9027 -0.0013 0.0008 0.0030
Low frequencies --- 1088.3853 1693.7756 1693.7756</pre>

[[File:Em316 Ir spectrum of nh3.PNG]]

{| class="wikitable"
|+
|-
|wavenumber (cm-1 || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1088
|146
|A1
|yes
|out-of-plane bend
|-
|1694
|14
|E
|very slight
|bend
|-
|1694
|14
|E
|very slight
|bend
|-
|3462
|1
|A1
|no
|symmetric stretch
|-
|3591
|0
|E
|Yes
|asymmetric stretch
|-
|3591
|0
|E
|Yes
|asymmetric stretch
|}

==NH3BH3==

===Method: B3LYP Basis set: 6-21G(d,p)===

[[File:Em316 nh3bh3 6 21G OPT.PNG]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>NH3BH3 6 21G OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

<pre> Item Value Threshold Converged?
Maximum Force 0.000131 0.000450 YES
RMS Force 0.000037 0.000300 YES
Maximum Displacement 0.000654 0.001800 YES
RMS Displacement 0.000179 0.001200 YES
Predicted change in Energy=-1.115346D-07 </pre>

'''Vibrational spectrum'''
{| class="wikitable"
|+
|-
|wavenumber (cm-1 || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|264
|0
|A2
|no
|N-B rotation
|-
|634
|14
|E
|slight
|N-B stretching
|-
|639
|4
|E
|very slight
|N-B twsting
|-
|639
|4
|A1
|very slight
|N-B rocking
|-
|1069
|41
|E
|Yes
|N-B twsting
|-
|1069
|41
|E
|Yes
|N-B rocking
|-
|1196
|108
|E
|Yes
|B-H out-of-plane bend
|-
|1204
|3
|E
|very slight
|N-H bend
|-
|1204
|3
|E
|very slight
|N-H bend
|-
|1330
|113
|E
|Yes
|N-H out-of-plane bend
|-
|1676
|28
|E
|Yes
|N-H bend
|-
|1676
|28
|E
|Yes
|N-H bend
|-
|2472
|67
|E
|Yes
|B-H symmetric stretch
|-
|2532
|231
|E
|Yes
|B-H asymmetric stretch
|-
|2532
|231
|E
|Yes
|B-H asymmetric stretch
|-
|3464
|2
|E
|very slight
|N-H symmetric stretch
|-
|3580
|28
|E
|Yes
|N-H asymmetric stretch
|-
|3580
|28
|E
|Yes
|N-H asymmetric stretch
|}

[[File:Em316 bh3 IR spectrum.PNG]]

===Energy Calculation===
E(NH3)= -26.46226 a.u.
E(BH3)= -56.55776 a.u.
E(NH3BH3)= -83.22468 a.u.

ΔE=E(NH3BH3)-[E(NH3)+E(BH3)]
=-83.22468 -(-26.46226 + -56.55776)
=-0.20466 a.u.
=-537.33483 kJ/mol

The bond dissociation energy has a negative value as it's an exothermic reaction. The calculated value is negative which fits in with the theory. Also the bond strength varies between 3-1000 kl/mol therefore -537 kJ/mol is a sensible value for a bond dissociation energy.

* Based on your energy calculation is the B-N dative bond weak, medium or strong? What comparison have you made to come to this conclusion?
The energy of B-N bond is medium. One of the strong bonds NΞN dissociation energy is 945 kJ/mol and C-O bond's dissociation energy is 1077 kJ/mol. Weak bonds such as Br-Br has a bond dissociation energy value of 192 kJ/mol.<ref>https://en.wikipedia.org/wiki/Bond-dissociation_energy</ref> B-N bond has a dissociation energy value in between the strong and weak bond dissociation energy, therefore, B-N bond energy is medium.

==BBr3==
====Method: B3LYP Basis set: 6-21G GEN====

[[File:Bbr3 summary em316.PNG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000001 0.000450 YES
RMS Force 0.000001 0.000300 YES
Maximum Displacement 0.000006 0.001800 YES
RMS Displacement 0.000004 0.001200 YES
Predicted change in Energy=-1.206088D-11
Optimization completed. </pre>

<pre>Low frequencies --- -0.0116 -0.0065 -0.0004 49.9506 49.9506 50.0315
Low frequencies --- 144.7606 144.7640 215.6181</pre>

[[Media:BBr3 plswork web OPt.log| BBr3 optimised.log]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>BBr3 plswork web OPt.log</uploadedFileContents>
</jmolApplet></jmol>

==Aromaticity==
===Benzene===

====Method: B3LYP Basis set: 6-21G(d,p)====

[[File:Benzene summary table.PNG]]

[[Media:EM316 BENZENE 6 21G FREQMO.LOG| EM316 BENZENE 6 21G OPT.LOG]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 BENZENE 6 21G FREQMO.LOG</uploadedFileContents>
</jmolApplet></jmol>

<pre> Item Value Threshold Converged?
Maximum Force 0.000049 0.000450 YES
RMS Force 0.000021 0.000300 YES
Maximum Displacement 0.000068 0.001800 YES
RMS Displacement 0.000030 0.001200 YES
Predicted change in Energy=-8.796913D-09 </pre>

=====Frequency Analysis====

<pre>Low frequencies --- -11.2053 -7.2445 -7.2445 -0.0055 -0.0055 -0.0007
Low frequencies --- 414.4985 414.4985 621.0620
Diagonal vibrational polarizability:
0.2795691 0.2795903 4.1346737
Harmonic frequencies (cm**-1), IR intensities (KM/Mole), Raman scattering
activities (A**4/AMU), depolarization ratios for plane and unpolarized
incident light, reduced masses (AMU), force constants (mDyne/A),
and normal coordinates:
1 2 3
E2U E2U E2G
Frequencies -- 414.4985 414.4985 621.0620
Red. masses -- 2.9462 2.9462 6.0756
Frc consts -- 0.2982 0.2982 1.3807
IR Inten -- 0.0000 0.0000 0.0000</pre>

===Borazine===

====Method: B3LYP Basis set: 6-21G(d,p)====

[[File:Borazine results table.PNG]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 BORAZINE 6 21G FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

[[Media:EM316 BORAZINE 6 21G FREQ.LOG| EM316 BORAZINE 6 21G.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000290 0.000450 YES
RMS Force 0.000119 0.000300 YES
Maximum Displacement 0.000581 0.001800 YES
RMS Displacement 0.000278 0.001200 YES
Predicted change in Energy=-4.469792D-07 </pre>

====Frequency Analysis====

<pre>Low frequencies --- -14.2714 -13.9795 -10.8868 -0.0110 0.0326 0.0561
Low frequencies --- 289.1178 289.1292 404.2716
Diagonal vibrational polarizability:
7.3588310 7.3578646 14.1611762
Harmonic frequencies (cm**-1), IR intensities (KM/Mole), Raman scattering
activities (A**4/AMU), depolarization ratios for plane and unpolarized
incident light, reduced masses (AMU), force constants (mDyne/A),
and normal coordinates:
1 2 3
E" E" A2"
Frequencies -- 289.1170 289.1284 404.2716
Red. masses -- 2.9298 2.9298 1.9279
Frc consts -- 0.1443 0.1443 0.1856
IR Inten -- 0.0000 0.0000 23.7973</pre>

====Benzene and Borazine comparison====

=====Charge distribution=====
[[File:Charge comparison3 em316.PNG|500px|center]]

The charge distribution on benzene is: C= -0.084 eV, H = 0084. eV
For the Borazine: B= 0.747 eV, N= -1.102 eV, H(N-H)= 0.432 eV, H(B-H)= -0.077 eV

For benzene all the carbon molecule has a same charge; -0.084 eV. And the charge is negative as carbon is more electronegative than hydrogen thus there's more electron density on carbon than the hydrogen.

The charge differences in borazine can be explained through the same principle: nitrogen is more electronegative than both boron and hydrogen thus it has the most negative charge. Therefore the charge on hydrogen of N-H bond is slightly more positive than the hydrogen in B-H bond: the electron density on hydrogen is pulled towards the electronegative nitrogen. On the other hand, boron is less electronegative than hydrogen so B-H hydrogen has slightly negative charge.

=====Molecular Orbitals=====

{| class="wikitable"
|+
|-
|MO || Benzene || Borazine || Description
|-
|MO11
|[[File:Mo11 benzene em316.PNG|200px]]
|[[File:MO11 borazine em316.PNG|200px]]
|MO11 shows both bonding and antibonding MO for both complexes.
The benzene MO is very symmetric with 2 nodes at the centre of carbon. There are in-phase overlap(bonding) of s atomic orbitals from 4 hydrogens and p atomic orbital from the 4 carbons on the both sides. There’s anti-bonding character as there are different phase orbitals(shown as red or green) close together.
The borazine MO has the similar characteristics but it’s less symmetrical. There’s am overlap between the top nitrogen p atomic orbital and s atomic orbitals of hydrogen.
|-
|MO17
|[[File:Mo17 benzene em316.PNG|200px]]
|[[File:Mo17 borazine em316.PNG|200px]]
|MO 17 ,again, has both bonding and small antibonding characteristic for both complexes. In benzene there are pz orbital contribution from carbon and no contribution from H atoms. As can be seen from each phase of orbital completely covering the carbon ring, the pz atomic orbitals are delocalised. There’s a nodal plane along the molecule.
The borazine’s MO is similar to the benzene’s with only boron and nitrogen’s p atomic orbital contributes to MO. This MO shows pi aspect of bonding.
|-
|MO20
|[[File:Mo20 benzene em316.PNG|200px]]
|[[File:MO20 borazine em316.PNG|200px]]
|MO20 have small bonding feature from 4 atoms. Both molecules have two nodal planes: through the centre and through the bonds. Therefore this MO has more antibonding characteristic than bonding. The benzene Mo is totally symmetric whereas the borazine’s one is not: the electron density is greater on the more electronegative nitrogen.
|}

=====Aromaticity=====

MO20 for both benzene and borazine, delocalised electron density above and below the nodal plane can be observed. This relates to the pi-electron delocalisation which is a common concept of aromatic molecules.

On the other hand, just relying on the overlap of Pz AOs to account for aromaticity is not suitable. The key concept of aromaticity is the aromatic stability which is result of pi-delocalisation. However, not only pi-electron structure contributes to the stability but sigma electron structure as well. <ref>Application of AIM Parameters at Ring Critical Points for Estimation ofp-Electron Delocalization in Six-Membered Aromatic andQuasi-Aromatic Rings,Palusick,M ,Krygowski,T ,</ref>

Also there are other factors which needs to be considered for a molecule to be aromatic:
The molecule must be cyclic. The ring needs to be planar. Each atom in the ring must be sp2-hybridised. The number of pi-electrons must obey the Huckle's rule(4n+2).<ref>https://chem.libretexts.org/Textbook_Maps/Organic_Chemistry_Textbook_Maps/Map%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)/Chapter_02%3A_Introduction_to_organic_structure_and_bonding_II/2.2%3A_Molecular_orbital_theory%3A_conjugation_and_aromaticity</ref>

[[File:Frost circle em316.PNG|500px|thumb|Benzene and Borazine in the Frost Circle]]

====Reference====
<references/>

2018-05-18T16:13:53Z

Em316:

==BH3==

====Method: B3LYP Basis set: 3-21G====

[[File:Em316 bh3 opt.PNG]]

[[Media:EM316 BH3 OPT.LOG| EM316 BH3 OPT.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000217 0.000450 YES
RMS Force 0.000105 0.000300 YES
Maximum Displacement 0.000900 0.001800 YES
RMS Displacement 0.000441 0.001200 YES </pre>

====Method: B3LYP Basis set: 6-21G====

[[File:Em316 bh3 sym opt 6 31G.PNG]]

[[Media:EM316 BH3 SYM OPT6 31G.LOG| EM316 BH3 SYM OPT6 31G.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000039 0.000450 YES
RMS Force 0.000025 0.000300 YES
Maximum Displacement 0.000153 0.001800 YES
RMS Displacement 0.000100 0.001200 YES </pre>

The frequencies below are the ones recalculated with the right symmetry

<pre> Low frequencies --- -19.6657 -16.7777 -16.7646 -0.0054 0.2513 0.6612
Low frequencies --- 1162.8624 1213.0925 1213.0952 </pre>

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 BH3 SYM OPT6 31G.LOG</uploadedFileContents>
</jmolApplet></jmol>

{| class="wikitable"
|+
|-
|wavenumber (cm-1 || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1163
|93
|A2
|yes
|out-of-plane bend
|-
|1213
|14
|E
|very slight
|bend
|-
|1213
|14
|E
|very slight
|bend
|-
|2583
|0
|A1
|no
|symmetric stretch
|-
|2716
|126
|E
|Yes
|asymmetric stretch
|-
|2716
|126
|E
|Yes
|asymmetric stretch
|}

[[File:Em316 bh3 IR spectrum.PNG]]

In the frequency table, there are 4 different frequencies observed: 1163, 1213, 2583 and 2716 cm-1 but in the IR spectrum there are only 3 peaks. These peaks correspond to 1163, 1213 and 2716 cm-1. The 2583cm-1 frequency IR inactive as it's a symmetric stretch and there's no change in dipole.

====MO diagram of BH3====

[[File:Em316 MO diagram complete.PNG|thumb|center|500px|MO diagram of BH3<ref>MO course handout, Trisha Hunt, 2017</ref>]]

* Are there any significant differences between the real and LCAO MOs?
There isn't mich differenced in the bonding orbital a'1, e' and non-bonding a"2 MOs. But the predicted MO of of antibonding orbital a'1 is differenct from the calculated orbital.

* What does this say about the accuracy and usefulness of qualitative MO theory?
The qualitative MO theory can predict the bonding and non-bonding orbitals accurately but anti-bonding MO may not be accurate.

==NH3==

===Method: B3LYP Basis set: 3-21G===
[[File:Nh3 first opt.PNG]]

[[Media:EM316 NH3 MOREOPT.LOG| NH3 3_21G OPT.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000057 0.000450 YES
RMS Force 0.000038 0.000300 YES
Maximum Displacement 0.000145 0.001800 YES
RMS Displacement 0.000096 0.001200 YES
Predicted change in Energy=-1.132410D-08 </pre>

==='''Method: B3LYP Basis set: 6-21G'''===

[[File:Nh3 first opt 6-31G.PNG]]

[[Media:EM316 NH3 OPT 6 31G.LOG| EM316 NH3 OPT 6 31G.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000060 0.000450 YES
RMS Force 0.000040 0.000300 YES
Maximum Displacement 0.000369 0.001800 YES
RMS Displacement 0.000162 0.001200 YES
Predicted change in Energy=-2.259205D-08 </pre>

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 NH3 OPT 6 31G.LOG</uploadedFileContents>
</jmolApplet></jmol>

'''Frequency Analysis'''
<pre>
Low frequencies --- -30.2442 -30.2441 -27.9027 -0.0013 0.0008 0.0030
Low frequencies --- 1088.3853 1693.7756 1693.7756</pre>

[[File:Em316 Ir spectrum of nh3.PNG]]

{| class="wikitable"
|+
|-
|wavenumber (cm-1 || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1088
|146
|A1
|yes
|out-of-plane bend
|-
|1694
|14
|E
|very slight
|bend
|-
|1694
|14
|E
|very slight
|bend
|-
|3462
|1
|A1
|no
|symmetric stretch
|-
|3591
|0
|E
|Yes
|asymmetric stretch
|-
|3591
|0
|E
|Yes
|asymmetric stretch
|}

==NH3BH3==

==='''Method: B3LYP Basis set: 6-21G'''===

[[File:Em316 nh3bh3 6 21G OPT.PNG]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>NH3BH3 6 21G OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

<pre> Item Value Threshold Converged?
Maximum Force 0.000131 0.000450 YES
RMS Force 0.000037 0.000300 YES
Maximum Displacement 0.000654 0.001800 YES
RMS Displacement 0.000179 0.001200 YES
Predicted change in Energy=-1.115346D-07 </pre>

'''Vibrational spectrum'''
{| class="wikitable"
|+
|-
|wavenumber (cm-1 || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|264
|0
|A2
|no
|N-B rotation
|-
|634
|14
|E
|slight
|N-B stretching
|-
|639
|4
|E
|very slight
|N-B twsting
|-
|639
|4
|A1
|very slight
|N-B rocking
|-
|1069
|41
|E
|Yes
|N-B twsting
|-
|1069
|41
|E
|Yes
|N-B rocking
|-
|1196
|108
|E
|Yes
|B-H out-of-plane bend
|-
|1204
|3
|E
|very slight
|N-H bend
|-
|1204
|3
|E
|very slight
|N-H bend
|-
|1330
|113
|E
|Yes
|N-H out-of-plane bend
|-
|1676
|28
|E
|Yes
|N-H bend
|-
|1676
|28
|E
|Yes
|N-H bend
|-
|2472
|67
|E
|Yes
|B-H symmetric stretch
|-
|2532
|231
|E
|Yes
|B-H asymmetric stretch
|-
|2532
|231
|E
|Yes
|B-H asymmetric stretch
|-
|3464
|2
|E
|very slight
|N-H symmetric stretch
|-
|3580
|28
|E
|Yes
|N-H asymmetric stretch
|-
|3580
|28
|E
|Yes
|N-H asymmetric stretch
|}

[[File:Em316 bh3 IR spectrum.PNG]]

===Energy Calculation===
E(NH3)= -26.46226 a.u.
E(BH3)= -56.55776 a.u.
E(NH3BH3)= -83.22468 a.u.

ΔE=E(NH3BH3)-[E(NH3)+E(BH3)]
=-83.22468 -(-26.46226 + -56.55776)
=-0.20466 a.u.
=-537.33483 kJ/mol

-So look at your number, is it a sensible value? How do you know what a sensible value is?
The bond dissociation energy has a negative value as it's an exothermic reaction. The calculated value is negative which fits in with the theory. Also the bond strength varies between 3-1000 kl/mol therefore -537 kJ/mol is a sensible value for a bond dissociation energy.

Based on your energy calculation is the B-N dative bond weak, medium or strong? What comparison have you made to come to this conclusion?
The energy of B-N bond is medium. One of the strong bonds NΞN dissociation energy is 945 kJ/mol and C-O bond's dissociation energy is 1077 kJ/mol. Weak bonds such as Br-Br has a bond dissociation energy value of 192 kJ/mol.<ref>https://en.wikipedia.org/wiki/Bond-dissociation_energy</ref> B-N bond has a dissociation energy value in between the strong and weak bond dissociation energy, therefore, B-N bond energy is medium.

==BBr3==
'''Method: B3LYP Basis set: 6-21G GEN'''

[[File:Bbr3 summary em316.PNG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000001 0.000450 YES
RMS Force 0.000001 0.000300 YES
Maximum Displacement 0.000006 0.001800 YES
RMS Displacement 0.000004 0.001200 YES
Predicted change in Energy=-1.206088D-11
Optimization completed. </pre>

[[Media:BBr3 plswork web OPt.log| BBr3 optimised.log]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>BBr3 plswork web OPt.log</uploadedFileContents>
</jmolApplet></jmol>

==Aromaticity==
===Benzene===

'''Method: B3LYP Basis set: 6-21G'''

[[File:Benzene summary table.PNG]]

[[Media:EM316 BENZENE 6 21G FREQMO.LOG| EM316 BENZENE 6 21G OPT.LOG]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 BENZENE 6 21G FREQMO.LOG</uploadedFileContents>
</jmolApplet></jmol>

<pre> Item Value Threshold Converged?
Maximum Force 0.000049 0.000450 YES
RMS Force 0.000021 0.000300 YES
Maximum Displacement 0.000068 0.001800 YES
RMS Displacement 0.000030 0.001200 YES
Predicted change in Energy=-8.796913D-09 </pre>

=====Frequency Analysis====

<pre>Low frequencies --- -11.2053 -7.2445 -7.2445 -0.0055 -0.0055 -0.0007
Low frequencies --- 414.4985 414.4985 621.0620
Diagonal vibrational polarizability:
0.2795691 0.2795903 4.1346737
Harmonic frequencies (cm**-1), IR intensities (KM/Mole), Raman scattering
activities (A**4/AMU), depolarization ratios for plane and unpolarized
incident light, reduced masses (AMU), force constants (mDyne/A),
and normal coordinates:
1 2 3
E2U E2U E2G
Frequencies -- 414.4985 414.4985 621.0620
Red. masses -- 2.9462 2.9462 6.0756
Frc consts -- 0.2982 0.2982 1.3807
IR Inten -- 0.0000 0.0000 0.0000</pre>

===Borazine===

'''Method: B3LYP Basis set: 6-21G'''

[[File:Borazine results table.PNG]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 BORAZINE 6 21G FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

[[Media:EM316 BORAZINE 6 21G FREQ.LOG| EM316 BORAZINE 6 21G.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000290 0.000450 YES
RMS Force 0.000119 0.000300 YES
Maximum Displacement 0.000581 0.001800 YES
RMS Displacement 0.000278 0.001200 YES
Predicted change in Energy=-4.469792D-07 </pre>

====Frequency Analysis====

<pre>Low frequencies --- -14.2714 -13.9795 -10.8868 -0.0110 0.0326 0.0561
Low frequencies --- 289.1178 289.1292 404.2716
Diagonal vibrational polarizability:
7.3588310 7.3578646 14.1611762
Harmonic frequencies (cm**-1), IR intensities (KM/Mole), Raman scattering
activities (A**4/AMU), depolarization ratios for plane and unpolarized
incident light, reduced masses (AMU), force constants (mDyne/A),
and normal coordinates:
1 2 3
E" E" A2"
Frequencies -- 289.1170 289.1284 404.2716
Red. masses -- 2.9298 2.9298 1.9279
Frc consts -- 0.1443 0.1443 0.1856
IR Inten -- 0.0000 0.0000 23.7973</pre>

====Benzene and Borazine comparison====

=====Charge distribution=====
[[File:Charge comparison3 em316.PNG]]

list and discuss the charges. The key words here are "compare" and "discuss" just presenting the tables is not sufficient, you must interpret your results.

The charge distribution on benzene is: C= -0.084 eV, H = 0084. eV
For the Borazine: B= 0.747 eV, N= -1.102 eV, H(N-H)= 0.432 eV, H(B-H)= -0.077 eV

For benzene all the carbon molecule has a same charge; -0.084 eV. And the charge is negative as carbon is more electronegative than hydrogen thus there's more electron density on carbon than the hydrogen.

The charge differences in borazine can be explained through the same principle: nitrogen is more electronegative than both boron and hydrogen thus it has the most negative charge. Therefore the charge on hydrogen of N-H bond is slightly more positive than the hydrogen in B-H bond: the electron density on hydrogen is pulled towards the electronegative nitrogen. On the other hand, boron is less electronegative than hydrogen so B-H hydrogen has slightly negative charge.

=====Molecular Orbitals=====

{| class="wikitable"
|+
|-
|MO || Benzene || Borazine || Description
|-
|MO11
|[[File:Mo11 benzene em316.PNG|200px]]
|[[File:MO11 borazine em316.PNG|200px]]
|MO11 shows both bonding and antibonding MO for both complexes.
The benzene MO is very symmetric with 2 nodes at the centre of carbon. There are in-phase overlap(bonding) of s atomic orbitals from 4 hydrogens and p atomic orbital from the 4 carbons on the both sides. There’s anti-bonding character as there are different phase orbitals(shown as red or green) close together.
The borazine MO has the similar characteristics but it’s less symmetrical. There’s am overlap between the top nitrogen p atomic orbital and s atomic orbitals of hydrogen.
|-
|MO17
|[[File:Mo17 benzene em316.PNG|200px]]
|[[File:Mo17 borazine em316.PNG|200px]]
|MO 17 ,again, has both bonding and small antibonding characteristic for both complexes. In benzene there are pz orbital contribution from carbon and no contribution from H atoms. As can be seen from each phase of orbital completely covering the carbon ring, the pz atomic orbitals are delocalised. There’s a nodal plane along the molecule.
The borazine’s MO is similar to the benzene’s with only boron and nitrogen’s p atomic orbital contributes to MO. This MO shows pi aspect of bonding.
|-
|MO20
|[[File:Mo20 benzene em316.PNG|200px]]
|[[File:MO20 borazine em316.PNG|200px]]
|MO20 have small bonding feature from 4 atoms. Both molecules have two nodal planes: through the centre and through the bonds. Therefore this MO has more antibonding characteristic than bonding. The benzene Mo is totally symmetric whereas the borazine’s one is not: the electron density is greater on the more electronegative nitrogen.
|}

=====Aromaticity=====

MO20 for both benzene and borazine, delocalised electron density above and below the nodal plane can be observed. This relates to the pi-electron delocalisation which is a common concept of aromatic molecules.

On the other hand, just relying on the overlap of Pz AOs to account for aromaticity is not suitable. The key concept of aromaticity is the aromatic stability which is result of pi-delocalisation. However, not only pi-electron structure contributes to the stability but sigma electron structure as well. <ref>Application of AIM Parameters at Ring Critical Points for Estimation ofp-Electron Delocalization in Six-Membered Aromatic andQuasi-Aromatic Rings,Palusick,M ,Krygowski,T ,</ref>

Also there are other factors which needs to be considered for a molecule to be aromatic:
The molecule must be cyclic. The ring needs to be planar. Each atom in the ring must be sp2-hybridised. The number of pi-electrons must obey the Huckle's rule(4n+2).<ref>https://chem.libretexts.org/Textbook_Maps/Organic_Chemistry_Textbook_Maps/Map%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)/Chapter_02%3A_Introduction_to_organic_structure_and_bonding_II/2.2%3A_Molecular_orbital_theory%3A_conjugation_and_aromaticity</ref>

File:BBr3 plswork web OPt.log

2018-05-18T16:13:07Z

Em316:

File:Bbr3 summary em316.PNG

2018-05-18T16:10:44Z

Em316:

File:Charge comparison3 em316.PNG

2018-05-18T15:49:19Z

Em316:

Rep:Title=Mod:eunicemoon316

2018-05-18T15:48:46Z

Em316:

==BH3==

===='''Method: B3LYP Basis set: 3-21G'''====

[[File:Em316 bh3 opt.PNG]]

[[Media:EM316 BH3 OPT.LOG| EM316 BH3 OPT.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000217 0.000450 YES
RMS Force 0.000105 0.000300 YES
Maximum Displacement 0.000900 0.001800 YES
RMS Displacement 0.000441 0.001200 YES </pre>

===='''Method: B3LYP Basis set: 6-21G'''====

[[File:Em316 bh3 sym opt 6 31G.PNG]]

[[Media:EM316 BH3 SYM OPT6 31G.LOG| EM316 BH3 SYM OPT6 31G.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000039 0.000450 YES
RMS Force 0.000025 0.000300 YES
Maximum Displacement 0.000153 0.001800 YES
RMS Displacement 0.000100 0.001200 YES </pre>

The frequencies below are the ones recalculated with the right symmetry

<pre> Low frequencies --- -19.6657 -16.7777 -16.7646 -0.0054 0.2513 0.6612
Low frequencies --- 1162.8624 1213.0925 1213.0952 </pre>

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 BH3 SYM OPT6 31G.LOG</uploadedFileContents>
</jmolApplet></jmol>

{| class="wikitable"
|+
|-
|wavenumber (cm-1 || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1163
|93
|A2
|yes
|out-of-plane bend
|-
|1213
|14
|E
|very slight
|bend
|-
|1213
|14
|E
|very slight
|bend
|-
|2583
|0
|A1
|no
|symmetric stretch
|-
|2716
|126
|E
|Yes
|asymmetric stretch
|-
|2716
|126
|E
|Yes
|asymmetric stretch
|}

[[File:Em316 bh3 IR spectrum.PNG]]

In the frequency table, there are 4 different frequencies observed: 1163, 1213, 2583 and 2716 cm-1 but in the IR spectrum there are only 3 peaks. These peaks correspond to 1163, 1213 and 2716 cm-1. The 2583cm-1 frequency IR inactive as it's a symmetric stretch and there's no change in dipole.

====MO diagram of BH3====

[[File:Em316 MO diagram complete.PNG|thumb|center|500px|MO diagram of BH3<ref>MO course handout, Trisha Hunt, 2017</ref>]]

* Are there any significant differences between the real and LCAO MOs?
There isn't mich differenced in the bonding orbital a'1, e' and non-bonding a"2 MOs. But the predicted MO of of antibonding orbital a'1 is differenct from the calculated orbital.

* What does this say about the accuracy and usefulness of qualitative MO theory?
The qualitative MO theory can predict the bonding and non-bonding orbitals accurately but anti-bonding MO may not be accurate.

===NH3===

===='''Method: B3LYP Basis set: 3-21G'''====
[[File:Nh3 first opt.PNG]]

[[Media:EM316 NH3 MOREOPT.LOG| NH3 3_21G OPT.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000057 0.000450 YES
RMS Force 0.000038 0.000300 YES
Maximum Displacement 0.000145 0.001800 YES
RMS Displacement 0.000096 0.001200 YES
Predicted change in Energy=-1.132410D-08 </pre>

===='''Method: B3LYP Basis set: 6-21G'''====

[[File:Nh3 first opt 6-31G.PNG]]

[[Media:EM316 NH3 OPT 6 31G.LOG| EM316 NH3 OPT 6 31G.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000060 0.000450 YES
RMS Force 0.000040 0.000300 YES
Maximum Displacement 0.000369 0.001800 YES
RMS Displacement 0.000162 0.001200 YES
Predicted change in Energy=-2.259205D-08 </pre>

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 NH3 OPT 6 31G.LOG</uploadedFileContents>
</jmolApplet></jmol>

'''Frequency Analysis'''
<pre>
Low frequencies --- -30.2442 -30.2441 -27.9027 -0.0013 0.0008 0.0030
Low frequencies --- 1088.3853 1693.7756 1693.7756</pre>

[[File:Em316 Ir spectrum of nh3.PNG]]

{| class="wikitable"
|+
|-
|wavenumber (cm-1 || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1088
|146
|A1
|yes
|out-of-plane bend
|-
|1694
|14
|E
|very slight
|bend
|-
|1694
|14
|E
|very slight
|bend
|-
|3462
|1
|A1
|no
|symmetric stretch
|-
|3591
|0
|E
|Yes
|asymmetric stretch
|-
|3591
|0
|E
|Yes
|asymmetric stretch
|}

===NH3BH3===

===='''Method: B3LYP Basis set: 6-21G'''====

[[File:Em316 nh3bh3 6 21G OPT.PNG]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>NH3BH3 6 21G OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

<pre> Item Value Threshold Converged?
Maximum Force 0.000131 0.000450 YES
RMS Force 0.000037 0.000300 YES
Maximum Displacement 0.000654 0.001800 YES
RMS Displacement 0.000179 0.001200 YES
Predicted change in Energy=-1.115346D-07 </pre>

'''Vibrational spectrum'''
{| class="wikitable"
|+
|-
|wavenumber (cm-1 || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|264
|0
|A2
|no
|N-B rotation
|-
|634
|14
|E
|slight
|N-B stretching
|-
|639
|4
|E
|very slight
|N-B twsting
|-
|639
|4
|A1
|very slight
|N-B rocking
|-
|1069
|41
|E
|Yes
|N-B twsting
|-
|1069
|41
|E
|Yes
|N-B rocking
|-
|1196
|108
|E
|Yes
|B-H out-of-plane bend
|-
|1204
|3
|E
|very slight
|N-H bend
|-
|1204
|3
|E
|very slight
|N-H bend
|-
|1330
|113
|E
|Yes
|N-H out-of-plane bend
|-
|1676
|28
|E
|Yes
|N-H bend
|-
|1676
|28
|E
|Yes
|N-H bend
|-
|2472
|67
|E
|Yes
|B-H symmetric stretch
|-
|2532
|231
|E
|Yes
|B-H asymmetric stretch
|-
|2532
|231
|E
|Yes
|B-H asymmetric stretch
|-
|3464
|2
|E
|very slight
|N-H symmetric stretch
|-
|3580
|28
|E
|Yes
|N-H asymmetric stretch
|-
|3580
|28
|E
|Yes
|N-H asymmetric stretch
|}

[[File:Em316 bh3 IR spectrum.PNG]]

====Energy Calculation====
E(NH3)= -26.46226 a.u.
E(BH3)= -56.55776 a.u.
E(NH3BH3)= -83.22468 a.u.

ΔE=E(NH3BH3)-[E(NH3)+E(BH3)]
=-83.22468 -(-26.46226 + -56.55776)
=-0.20466 a.u.
=-537.33483 kJ/mol

-So look at your number, is it a sensible value? How do you know what a sensible value is?
The bond dissociation energy has a negative value as it's an exothermic reaction. The calculated value is negative which fits in with the theory. Also the bond strength varies between 3-1000 kl/mol therefore -537 kJ/mol is a sensible value for a bond dissociation energy.

Based on your energy calculation is the B-N dative bond weak, medium or strong? What comparison have you made to come to this conclusion?
The energy of B-N bond is medium. One of the strong bonds NΞN dissociation energy is 945 kJ/mol and C-O bond's dissociation energy is 1077 kJ/mol. Weak bonds such as Br-Br has a bond dissociation energy value of 192 kJ/mol.<ref>https://en.wikipedia.org/wiki/Bond-dissociation_energy</ref> B-N bond has a dissociation energy value in between the strong and weak bond dissociation energy, therefore, B-N bond energy is medium.

==BBr3==
'''Method: B3LYP Basis set: 6-21G GEN'''

[[Media:Web Opt BBr3 log 10047526.log| BBr3 optimised.log]]

===Aromaticity===
====Benzene====

'''Method: B3LYP Basis set: 6-21G'''

[[File:Benzene summary table.PNG]]

[[Media:EM316 BENZENE 6 21G FREQMO.LOG| EM316 BENZENE 6 21G OPT.LOG]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 BENZENE 6 21G FREQMO.LOG</uploadedFileContents>
</jmolApplet></jmol>

<pre> Item Value Threshold Converged?
Maximum Force 0.000049 0.000450 YES
RMS Force 0.000021 0.000300 YES
Maximum Displacement 0.000068 0.001800 YES
RMS Displacement 0.000030 0.001200 YES
Predicted change in Energy=-8.796913D-09 </pre>

=====Frequency Analysis====

<pre>Low frequencies --- -11.2053 -7.2445 -7.2445 -0.0055 -0.0055 -0.0007
Low frequencies --- 414.4985 414.4985 621.0620
Diagonal vibrational polarizability:
0.2795691 0.2795903 4.1346737
Harmonic frequencies (cm**-1), IR intensities (KM/Mole), Raman scattering
activities (A**4/AMU), depolarization ratios for plane and unpolarized
incident light, reduced masses (AMU), force constants (mDyne/A),
and normal coordinates:
1 2 3
E2U E2U E2G
Frequencies -- 414.4985 414.4985 621.0620
Red. masses -- 2.9462 2.9462 6.0756
Frc consts -- 0.2982 0.2982 1.3807
IR Inten -- 0.0000 0.0000 0.0000</pre>

====Borazine====

'''Method: B3LYP Basis set: 6-21G'''

[[File:Borazine results table.PNG]]

<jmol><jmolApplet>
<title>Optimised BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>EM316 BORAZINE 6 21G FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

[[Media:EM316 BORAZINE 6 21G FREQ.LOG| EM316 BORAZINE 6 21G.LOG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000290 0.000450 YES
RMS Force 0.000119 0.000300 YES
Maximum Displacement 0.000581 0.001800 YES
RMS Displacement 0.000278 0.001200 YES
Predicted change in Energy=-4.469792D-07 </pre>

=====Frequency Analysis=====

<pre>Low frequencies --- -14.2714 -13.9795 -10.8868 -0.0110 0.0326 0.0561
Low frequencies --- 289.1178 289.1292 404.2716
Diagonal vibrational polarizability:
7.3588310 7.3578646 14.1611762
Harmonic frequencies (cm**-1), IR intensities (KM/Mole), Raman scattering
activities (A**4/AMU), depolarization ratios for plane and unpolarized
incident light, reduced masses (AMU), force constants (mDyne/A),
and normal coordinates:
1 2 3
E" E" A2"
Frequencies -- 289.1170 289.1284 404.2716
Red. masses -- 2.9298 2.9298 1.9279
Frc consts -- 0.1443 0.1443 0.1856
IR Inten -- 0.0000 0.0000 23.7973</pre>

====Benzene and Borazine comparison====

=====Charge distribution=====
[[File:Charge comparison2.PNG]]

list and discuss the charges. The key words here are "compare" and "discuss" just presenting the tables is not sufficient, you must interpret your results.

The charge distribution on benzene is: C= -0.239 eV, H = 0.239 eV
For the Borazine: B= 0.747 eV, N= -1.102 eV, H(N-H)= 0.432 eV, H(B-H)= -0.077 eV

For benzene all the carbon molecule has a same charge; -0.239 eV. And the charge is negative as carbon is more electronegative than hydrogen thus there's more electron density on carbon than the hydrogen.

The charge differences in borazine can be explained through the same principle: nitrogen is more electronegative than both boron and hydrogen thus it has the most negative charge. Therefore the charge on hydrogen of N-H bond is slightly more positive than the hydrogen in B-H bond: the electron density on hydrogen is pulled towards the electronegative nitrogen. On the other hand, boron is less electronegative than hydrogen so B-H hydrogen has slightly negative charge.

=====Molecular Orbitals=====

{| class="wikitable"
|+
|-
|MO || Benzene || Borazine || Description
|-
|MO11
|[[File:Mo11 benzene em316.PNG|200px]]
|[[File:MO11 borazine em316.PNG|200px]]
|MO11 shows both bonding and antibonding MO for both complexes.
The benzene MO is very symmetric with 2 nodes at the centre of carbon. There are in-phase overlap(bonding) of s atomic orbitals from 4 hydrogens and p atomic orbital from the 4 carbons on the both sides. There’s anti-bonding character as there are different phase orbitals(shown as red or green) close together.
The borazine MO has the similar characteristics but it’s less symmetrical. There’s am overlap between the top nitrogen p atomic orbital and s atomic orbitals of hydrogen.
|-
|MO17
|[[File:Mo17 benzene em316.PNG|200px]]
|[[File:Mo17 borazine em316.PNG|200px]]
|MO 17 ,again, has both bonding and small antibonding characteristic for both complexes. In benzene there are pz orbital contribution from carbon and no contribution from H atoms. As can be seen from each phase of orbital completely covering the carbon ring, the pz atomic orbitals are delocalised. There’s a nodal plane along the molecule.
The borazine’s MO is similar to the benzene’s with only boron and nitrogen’s p atomic orbital contributes to MO. This MO shows pi aspect of bonding.
|-
|MO20
|[[File:Mo20 benzene em316.PNG|200px]]
|[[File:MO20 borazine em316.PNG|200px]]
|MO20 have small bonding feature from 4 atoms. Both molecules have two nodal planes: through the centre and through the bonds. Therefore this MO has more antibonding characteristic than bonding. The benzene Mo is totally symmetric whereas the borazine’s one is not: the electron density is greater on the more electronegative nitrogen.
|}

'''Aromaticity'''

MO20 for both benzene and borazine, delocalised electron density above and below the nodal plane can be observed. This relates to the pi-electron delocalisation which is a common concept of aromatic molecules.

On the other hand, just relying on the overlap of Pz AOs to account for aromaticity is not suitable. The key concept of aromaticity is the aromatic stability which is result of pi-delocalisation. However, not only pi-electron structure contributes to the stability but sigma electron structure as well. <ref>Application of AIM Parameters at Ring Critical Points for Estimation ofp-Electron Delocalization in Six-Membered Aromatic andQuasi-Aromatic Rings</ref>

Also there are other factors which needs to be considered for a molecule to be aromatic:
The molecule must be cyclic. The ring needs to be planar. Each atom in the ring must be sp2-hybridised. The number of pi-electrons must obey the Huckle's rule(4n+2).<ref>https://chem.libretexts.org/Textbook_Maps/Organic_Chemistry_Textbook_Maps/Map%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)/Chapter_02%3A_Introduction_to_organic_structure_and_bonding_II/2.2%3A_Molecular_orbital_theory%3A_conjugation_and_aromaticity</ref>

2018-05-18T13:42:54Z

Em316:

File:Mo20 benzene em316.PNG

2018-05-18T13:42:30Z

Em316:

File:Mo17 borazine em316.PNG

2018-05-18T13:41:48Z

Em316:

File:Mo17 benzene em316.PNG

2018-05-18T13:41:22Z

Em316:

File:MO11 borazine em316.PNG

2018-05-18T13:38:37Z

Em316: