Rep:Mod:t3gy216

2018-05-24T12:10:35Z

Gy216: /* Molecular Orbital Comparison */

2018-05-23T19:48:05Z

Gy216: /* Molecular Orbital Comparison */

== BH3 ==

'''Calculation Method and Basis Set: B3LYP/6-31G(d,p)'''

[[File:Gyu_bh3_opt_631g_dp.PNG]]

<pre>Item Value Threshold Converged?
Maximum Force 0.000014 0.000450 YES
RMS Force 0.000009 0.000300 YES
Maximum Displacement 0.000057 0.001800 YES
RMS Displacement 0.000037 0.001200 YES</pre>

=== Frequency Analysis ===

[[Media:GLYNISYU_BH3_FREQ.LOG|Frequency analysis log file here]]

<pre>Low frequencies --- -10.0419 -2.9960 -0.0054 0.4925 2.1764 3.7030
Low frequencies --- 1162.9539 1213.1540 1213.1567 </pre>

<jmol><jmolApplet>
<title>Optimised BH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>GLYNISYU_BH3_FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

'''Vibrational spectrum for BH3'''
{| 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
|-
|2582
|0
|A1'
|No
|Symmetric stretch
|-
|2716
|126
|E'
|Yes
|Asymmetric stretch
|-
|2716
|126
|E'
|Yes
|Asymmetric stretch
|}

[[File:Gyu_bh3_vib_spectrum.PNG]]

Although there are 6 vibrations, only 3 show up in the IR spectrum. One of the visible peaks is due to the a2'' bend. The a1 stretch is not IR active as there is no change in dipole moment. The last two peaks are due to the e' bends and stretches. As both e' bends and both e' stretches are degenerate, only one peak arises for each set of degenerate bends/stretches.

'''Molecular Orbital Diagram for BH3'''
[[File:Gyu_bh3_mo_diagram2.jpeg|750px]]<ref name="MO_diagram"/>

Looking at the diagram shown above, there is resemblance between the real MOs and predicted MOs by LCAO. The predicted MOs accurately depict the shape and phase of the electron distribution shown in the computationally analysed orbitals. This shows that using qualitative MO theory is a useful and accurate way of predicting molecular orbitals.

<references>
<ref name="MO_diagram">The original MO diagram can be found here [http://www.huntresearchgroup.org.uk/teaching/teaching_comp_lab_year2a/Tut_MO_diagram_BH3.pdf]</ref>
</references>

== NH3 ==

'''Calculation method and basis set: B3LYP/6-31G(d,p)'''

[[File:Gyu_nh3_opt_631g_dp.PNG]]

<pre>Item Value Threshold Converged?
Maximum Force 0.000006 0.000450 YES
RMS Force 0.000004 0.000300 YES
Maximum Displacement 0.000012 0.001800 YES
RMS Displacement 0.000008 0.001200 YES
</pre>

=== Frequency Analysis ===

[[Media:GLYNISYU_NH3_FREQ.LOG|Frequency analysis log file here]]

<pre>Low frequencies --- -8.5646 -8.5588 -0.0041 0.0455 0.1784 26.4183
Low frequencies --- 1089.7603 1694.1865 1694.1865</pre>

<jmol><jmolApplet>
<title>Optimised NH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>GLYNISYU_NH3_FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

== NH3BH3 ==

'''Calculation method and basis set: B3LYP/6-31G(d,p)'''

[[File:Gyu_nh3bh3_opt_631g_dp.PNG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000122 0.000450 YES
RMS Force 0.000058 0.000300 YES
Maximum Displacement 0.000540 0.001800 YES
RMS Displacement 0.000297 0.001200 YES</pre>

=== Frequency Analysis ===

[[Media:GYU_NH3BH3_FREQ.LOG|Frequency analysis log file here]]

<pre>Low frequencies --- -0.0571 -0.0499 -0.0075 21.7150 21.7251 40.6257
Low frequencies --- 266.0444 632.3706 640.1455</pre>

<jmol><jmolApplet>
<title>Optimised NH3BH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>GYU_NH3BH3_FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

=== Calculations ===

{| class="wikitable" border="1"
! Molecule!! Energy (au)
|-
| BH3 || -26.61532
|-
| NH3 || -56.55777
|-
| NH3BH3 || -83.22469
|}

The bond association energy can be calculated using ΔE=E(NH3BH3)-[E(NH3)+E(BH3)].

ΔE = -83.22469-(-26.61532+-56.55777) = -0.0516 au

In kJmol-1, the bond association energy comes out to be -135 kJmol-1

The calculated bond dissociation energy for the B-N dative bond is 135 kJmol-1. Comparison to the bond dissociation energy of a Br-Br bond (192 kJmol-1) indicates that the B-N bond is weak, as the dissociation energy is even smaller than that for Br-Br<ref name="Br_Br"/>.

<references>
<ref name="Br_Br">The bond dissociation energy of Br-Br can be found here [https://en.wikipedia.org/wiki/Bond-dissociation_energy]</ref>/
</references>

== BBr3 ==

'''Calculation method and basis set: B3LYP/6-31G(d,p)'''

[[File:Gyu_bbr3_opt_631g_dp.PNG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000008 0.000450 YES
RMS Force 0.000005 0.000300 YES
Maximum Displacement 0.000036 0.001800 YES
RMS Displacement 0.000023 0.001200 YES</pre>

=== Frequency Analysis ===

[[Media: Gyu_bbr3_freq_server.log|Frequency Analysis log file here]]

<pre> Low frequencies --- -0.0137 -0.0064 -0.0046 2.4315 2.4315 4.8421
Low frequencies --- 155.9631 155.9651 267.7052</pre>

<jmol><jmolApplet>
<title>Optimised BBr3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>Gyu_bbr3_freq_server.log</uploadedFileContents>
</jmolApplet></jmol>

Link to Dspace: http://hdl.handle.net/10042/202448

{{DOI|10042/202448}}

== Project Section: Aromaticity ==

=== Benzene ===

'''Calculation method and basis set: B3LYP/6-31G(d,p)'''

[[File:Gyu_benzene_opt_631g_dp.PNG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000194 0.000450 YES
RMS Force 0.000077 0.000300 YES
Maximum Displacement 0.000824 0.001800 YES
RMS Displacement 0.000289 0.001200 YES</pre>

==== Frequency Analysis ====

[[Media: GYU_BENZENE_FREQ_631G_DP.LOG|Frequency Analysis log file here]]

<pre>Low frequencies --- -2.1456 -2.1456 -0.0087 -0.0042 -0.0041 10.4835
Low frequencies --- 413.9768 413.9768 621.1390</pre>

<jmol><jmolApplet>
<title>Optimised Benzene molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>GYU_BENZENE_FREQ_631G_DP.LOG</uploadedFileContents>
</jmolApplet></jmol>

=== Borazine ===

'''Calculation method and basis set: B3LYP/6-31G(d,p)'''

[[File:Gyu_borazine_opt_631g_dp.PNG]]

<pre>Item Value Threshold Converged?
Maximum Force 0.000011 0.000450 YES
RMS Force 0.000005 0.000300 YES
Maximum Displacement 0.000065 0.001800 YES
RMS Displacement 0.000021 0.001200 YES</pre>

==== Frequency Analysis ====

[[Media:GYU_BORAZINE_FREQ_631G_DP.LOG|Frequency analysis log file here]]

<pre>Low frequencies --- -13.9554 -13.7954 -10.4509 -0.0104 -0.0091 0.0726
Low frequencies --- 289.0422 289.0509 403.8550</pre>

<jmol><jmolApplet>
<title>Optimised Borazine molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>GYU_BORAZINE_FREQ_631G_DP.LOG</uploadedFileContents>
</jmolApplet></jmol>

=== Benzene vs. Borazine ===

==== Charge Distribution ====

{| class="wikitable" border="1"
! Benzene !! Borazine
|-
| [[File:Gyu_Benzene_1.102_colour.PNG]] || [[File:Gyu_Borazine_1.102_colour.PNG]]
|-
| Carbon Charge: -0.239 || Boron Charge: 0.747
|-
| Hydrogen Charge: 0.239 || Nitrogen Charge: -1.102
|-
| - || Hydrogen Charge (bonded to B): -0.077
|-
| - || Hydrogen Charge (bonded to N): 0.432
|}

In benzene, more electron density is located around the carbon atoms (-0.239) than the hydrogen atoms (0.239). This can be reasoned by comparing their relative electronegativities. Using the Pauling scale, carbon has a higher electronegativity (2.55) than hydrogen (2.20) and the values for the charge distribution of benzene reflects this; carbon has a negative charge distribution whilst hydrogen has a positive one. As benzene is symmetrical, all of the carbon atoms have the same electron distribution around them, as do the hydrogen atoms.

Unlike in benzene, the charge distribution around borazine is not symmetrical. The same argument of electronegativites can be used to explain this. From the elements in borazine, nitrogen has the largest electronegativity (3.04). When looking at the charge distribution of borazine above, the nitrogen atoms have the most negative values (-1.102), and so have the most electron density surrounding them. Boron has an electronegativity of 2.04. These boron atoms are located in between nitrogen atoms, therefore the charge distribution around boron is 0.747 as nitrogen is more electronegative, drawing electron density away from the boron atoms. The hydrogen atoms have different electron density around them, which depends on whether they are bonded to nitrogen or boron. The H atoms attached to boron have a negative value for charge distribution because hydrogen has a larger electronegativity than boron (2.20 to 2.04). The hydrogens attached to nitrogen have a positive charge distribution as nitrogen has a much greater electronegativity than hydrogen (3.04 to 2.20).

==== Molecular Orbital Comparison ====

{| class="wikitable" border="1"
! Benzene MO !! Borazine MO !! Description
|-
| [[File:Gyu_benzene_mo_13.PNG]] || [[File:Gyu_borazine_mo_16.PNG]] || Benzene MO13, Borazine MO16: These orbitals are similar in that they are both σ-antibonding MOs however, they differ in that they have different contributions from atoms. As benzene has D6h symmetry, the orbital contributions of each carbon and hydrogen is symmetric. However, in borazine the boron atoms have larger lobes since they have a lower electronegativity, contributing more to the antibonding orbitals than the nitrogen atoms (smaller lobes).
|-
| [[File:Gyu_benzene_mo_17.PNG]] || [[File:Gyu_borazine_mo_17.PNG]] || MO 17:
|-
| [[File:Gyu_benzene_homo_21.PNG]] || [[File:Gyu_borazine_homo_21.PNG]] || HOMO MO 21: The HOMO of benzene and borazine are very similar and are both π-bonding MOs. The main difference being that the benzene HOMO is entirely symmetric, whereas the borazine HOMO is skewed due to the difference in electronegativities of boron and nitrogen. Nitrogen has a higher electronegativity so there is a more concentrated area at the nitrogen atom, as it contributes more to the bonding orbital.
|}

Rep:Mod:t3gy216

2018-05-23T19:44:24Z

Gy216: /* Molecular Orbital Comparison */

== BH3 ==

'''Calculation Method and Basis Set: B3LYP/6-31G(d,p)'''

[[File:Gyu_bh3_opt_631g_dp.PNG]]

<pre>Item Value Threshold Converged?
Maximum Force 0.000014 0.000450 YES
RMS Force 0.000009 0.000300 YES
Maximum Displacement 0.000057 0.001800 YES
RMS Displacement 0.000037 0.001200 YES</pre>

=== Frequency Analysis ===

[[Media:GLYNISYU_BH3_FREQ.LOG|Frequency analysis log file here]]

<pre>Low frequencies --- -10.0419 -2.9960 -0.0054 0.4925 2.1764 3.7030
Low frequencies --- 1162.9539 1213.1540 1213.1567 </pre>

<jmol><jmolApplet>
<title>Optimised BH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>GLYNISYU_BH3_FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

'''Vibrational spectrum for BH3'''
{| 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
|-
|2582
|0
|A1'
|No
|Symmetric stretch
|-
|2716
|126
|E'
|Yes
|Asymmetric stretch
|-
|2716
|126
|E'
|Yes
|Asymmetric stretch
|}

[[File:Gyu_bh3_vib_spectrum.PNG]]

Although there are 6 vibrations, only 3 show up in the IR spectrum. One of the visible peaks is due to the a2'' bend. The a1 stretch is not IR active as there is no change in dipole moment. The last two peaks are due to the e' bends and stretches. As both e' bends and both e' stretches are degenerate, only one peak arises for each set of degenerate bends/stretches.

'''Molecular Orbital Diagram for BH3'''
[[File:Gyu_bh3_mo_diagram2.jpeg|750px]]<ref name="MO_diagram"/>

Looking at the diagram shown above, there is resemblance between the real MOs and predicted MOs by LCAO. The predicted MOs accurately depict the shape and phase of the electron distribution shown in the computationally analysed orbitals. This shows that using qualitative MO theory is a useful and accurate way of predicting molecular orbitals.

<references>
<ref name="MO_diagram">The original MO diagram can be found here [http://www.huntresearchgroup.org.uk/teaching/teaching_comp_lab_year2a/Tut_MO_diagram_BH3.pdf]</ref>
</references>

== NH3 ==

'''Calculation method and basis set: B3LYP/6-31G(d,p)'''

[[File:Gyu_nh3_opt_631g_dp.PNG]]

<pre>Item Value Threshold Converged?
Maximum Force 0.000006 0.000450 YES
RMS Force 0.000004 0.000300 YES
Maximum Displacement 0.000012 0.001800 YES
RMS Displacement 0.000008 0.001200 YES
</pre>

=== Frequency Analysis ===

[[Media:GLYNISYU_NH3_FREQ.LOG|Frequency analysis log file here]]

<pre>Low frequencies --- -8.5646 -8.5588 -0.0041 0.0455 0.1784 26.4183
Low frequencies --- 1089.7603 1694.1865 1694.1865</pre>

<jmol><jmolApplet>
<title>Optimised NH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>GLYNISYU_NH3_FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

== NH3BH3 ==

'''Calculation method and basis set: B3LYP/6-31G(d,p)'''

[[File:Gyu_nh3bh3_opt_631g_dp.PNG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000122 0.000450 YES
RMS Force 0.000058 0.000300 YES
Maximum Displacement 0.000540 0.001800 YES
RMS Displacement 0.000297 0.001200 YES</pre>

=== Frequency Analysis ===

[[Media:GYU_NH3BH3_FREQ.LOG|Frequency analysis log file here]]

<pre>Low frequencies --- -0.0571 -0.0499 -0.0075 21.7150 21.7251 40.6257
Low frequencies --- 266.0444 632.3706 640.1455</pre>

<jmol><jmolApplet>
<title>Optimised NH3BH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>GYU_NH3BH3_FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

=== Calculations ===

{| class="wikitable" border="1"
! Molecule!! Energy (au)
|-
| BH3 || -26.61532
|-
| NH3 || -56.55777
|-
| NH3BH3 || -83.22469
|}

The bond association energy can be calculated using ΔE=E(NH3BH3)-[E(NH3)+E(BH3)].

ΔE = -83.22469-(-26.61532+-56.55777) = -0.0516 au

In kJmol-1, the bond association energy comes out to be -135 kJmol-1

The calculated bond dissociation energy for the B-N dative bond is 135 kJmol-1. Comparison to the bond dissociation energy of a Br-Br bond (192 kJmol-1) indicates that the B-N bond is weak, as the dissociation energy is even smaller than that for Br-Br<ref name="Br_Br"/>.

<references>
<ref name="Br_Br">The bond dissociation energy of Br-Br can be found here [https://en.wikipedia.org/wiki/Bond-dissociation_energy]</ref>/
</references>

== BBr3 ==

'''Calculation method and basis set: B3LYP/6-31G(d,p)'''

[[File:Gyu_bbr3_opt_631g_dp.PNG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000008 0.000450 YES
RMS Force 0.000005 0.000300 YES
Maximum Displacement 0.000036 0.001800 YES
RMS Displacement 0.000023 0.001200 YES</pre>

=== Frequency Analysis ===

[[Media: Gyu_bbr3_freq_server.log|Frequency Analysis log file here]]

<pre> Low frequencies --- -0.0137 -0.0064 -0.0046 2.4315 2.4315 4.8421
Low frequencies --- 155.9631 155.9651 267.7052</pre>

<jmol><jmolApplet>
<title>Optimised BBr3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>Gyu_bbr3_freq_server.log</uploadedFileContents>
</jmolApplet></jmol>

Link to Dspace: http://hdl.handle.net/10042/202448

{{DOI|10042/202448}}

== Project Section: Aromaticity ==

=== Benzene ===

'''Calculation method and basis set: B3LYP/6-31G(d,p)'''

[[File:Gyu_benzene_opt_631g_dp.PNG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000194 0.000450 YES
RMS Force 0.000077 0.000300 YES
Maximum Displacement 0.000824 0.001800 YES
RMS Displacement 0.000289 0.001200 YES</pre>

==== Frequency Analysis ====

[[Media: GYU_BENZENE_FREQ_631G_DP.LOG|Frequency Analysis log file here]]

<pre>Low frequencies --- -2.1456 -2.1456 -0.0087 -0.0042 -0.0041 10.4835
Low frequencies --- 413.9768 413.9768 621.1390</pre>

<jmol><jmolApplet>
<title>Optimised Benzene molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>GYU_BENZENE_FREQ_631G_DP.LOG</uploadedFileContents>
</jmolApplet></jmol>

=== Borazine ===

'''Calculation method and basis set: B3LYP/6-31G(d,p)'''

[[File:Gyu_borazine_opt_631g_dp.PNG]]

<pre>Item Value Threshold Converged?
Maximum Force 0.000011 0.000450 YES
RMS Force 0.000005 0.000300 YES
Maximum Displacement 0.000065 0.001800 YES
RMS Displacement 0.000021 0.001200 YES</pre>

==== Frequency Analysis ====

[[Media:GYU_BORAZINE_FREQ_631G_DP.LOG|Frequency analysis log file here]]

<pre>Low frequencies --- -13.9554 -13.7954 -10.4509 -0.0104 -0.0091 0.0726
Low frequencies --- 289.0422 289.0509 403.8550</pre>

<jmol><jmolApplet>
<title>Optimised Borazine molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>GYU_BORAZINE_FREQ_631G_DP.LOG</uploadedFileContents>
</jmolApplet></jmol>

=== Benzene vs. Borazine ===

==== Charge Distribution ====

{| class="wikitable" border="1"
! Benzene !! Borazine
|-
| [[File:Gyu_Benzene_1.102_colour.PNG]] || [[File:Gyu_Borazine_1.102_colour.PNG]]
|-
| Carbon Charge: -0.239 || Boron Charge: 0.747
|-
| Hydrogen Charge: 0.239 || Nitrogen Charge: -1.102
|-
| - || Hydrogen Charge (bonded to B): -0.077
|-
| - || Hydrogen Charge (bonded to N): 0.432
|}

In benzene, more electron density is located around the carbon atoms (-0.239) than the hydrogen atoms (0.239). This can be reasoned by comparing their relative electronegativities. Using the Pauling scale, carbon has a higher electronegativity (2.55) than hydrogen (2.20) and the values for the charge distribution of benzene reflects this; carbon has a negative charge distribution whilst hydrogen has a positive one. As benzene is symmetrical, all of the carbon atoms have the same electron distribution around them, as do the hydrogen atoms.

Unlike in benzene, the charge distribution around borazine is not symmetrical. The same argument of electronegativites can be used to explain this. From the elements in borazine, nitrogen has the largest electronegativity (3.04). When looking at the charge distribution of borazine above, the nitrogen atoms have the most negative values (-1.102), and so have the most electron density surrounding them. Boron has an electronegativity of 2.04. These boron atoms are located in between nitrogen atoms, therefore the charge distribution around boron is 0.747 as nitrogen is more electronegative, drawing electron density away from the boron atoms. The hydrogen atoms have different electron density around them, which depends on whether they are bonded to nitrogen or boron. The H atoms attached to boron have a negative value for charge distribution because hydrogen has a larger electronegativity than boron (2.20 to 2.04). The hydrogens attached to nitrogen have a positive charge distribution as nitrogen has a much greater electronegativity than hydrogen (3.04 to 2.20).

==== Molecular Orbital Comparison ====

{| class="wikitable" border="1"
! Benzene MO !! Borazine MO !! Description
|-
| [[File:Gyu_benzene_mo_17.PNG]] || [[File:Gyu_borazine_mo_17.PNG]] ||
|-
| [[File:Gyu_benzene_mo_13.PNG]] || [[File:Gyu_borazine_mo_16.PNG]] || Benzene MO13, Borazine MO16: Both of these orbitals are σ-antibonding MOs. As benzene has D6h symmetry, the orbital contributions of each carbon and hydrogen is symmetric. However, in borazine the boron atoms have larger lobes since they have a lower electronegativity, contributing more to the antibonding orbitals.
|-
| [[File:Gyu_benzene_homo_21.PNG]] || [[File:Gyu_borazine_homo_21.PNG]] || HOMO MO 21: The HOMO of benzene and borazine are very similar and are both π-bonding MOs. The main difference being that the benzene HOMO is entirely symmetric, whereas the borazine HOMO is skewed due to the difference in electronegativities of boron and nitrogen. Nitrogen has a higher electronegativity so there is a more concentrated area at the nitrogen atom, as it contributes more to the bonding orbital.
|}

File:Gyu borazine mo 17.PNG

2018-05-23T19:44:01Z

Gy216:

Rep:Mod:t3gy216

2018-05-23T19:41:27Z

Gy216: /* Molecular Orbital Comparison */

== BH3 ==

'''Calculation Method and Basis Set: B3LYP/6-31G(d,p)'''

[[File:Gyu_bh3_opt_631g_dp.PNG]]

<pre>Item Value Threshold Converged?
Maximum Force 0.000014 0.000450 YES
RMS Force 0.000009 0.000300 YES
Maximum Displacement 0.000057 0.001800 YES
RMS Displacement 0.000037 0.001200 YES</pre>

=== Frequency Analysis ===

[[Media:GLYNISYU_BH3_FREQ.LOG|Frequency analysis log file here]]

<pre>Low frequencies --- -10.0419 -2.9960 -0.0054 0.4925 2.1764 3.7030
Low frequencies --- 1162.9539 1213.1540 1213.1567 </pre>

<jmol><jmolApplet>
<title>Optimised BH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>GLYNISYU_BH3_FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

'''Vibrational spectrum for BH3'''
{| 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
|-
|2582
|0
|A1'
|No
|Symmetric stretch
|-
|2716
|126
|E'
|Yes
|Asymmetric stretch
|-
|2716
|126
|E'
|Yes
|Asymmetric stretch
|}

[[File:Gyu_bh3_vib_spectrum.PNG]]

Although there are 6 vibrations, only 3 show up in the IR spectrum. One of the visible peaks is due to the a2'' bend. The a1 stretch is not IR active as there is no change in dipole moment. The last two peaks are due to the e' bends and stretches. As both e' bends and both e' stretches are degenerate, only one peak arises for each set of degenerate bends/stretches.

'''Molecular Orbital Diagram for BH3'''
[[File:Gyu_bh3_mo_diagram2.jpeg|750px]]<ref name="MO_diagram"/>

Looking at the diagram shown above, there is resemblance between the real MOs and predicted MOs by LCAO. The predicted MOs accurately depict the shape and phase of the electron distribution shown in the computationally analysed orbitals. This shows that using qualitative MO theory is a useful and accurate way of predicting molecular orbitals.

<references>
<ref name="MO_diagram">The original MO diagram can be found here [http://www.huntresearchgroup.org.uk/teaching/teaching_comp_lab_year2a/Tut_MO_diagram_BH3.pdf]</ref>
</references>

== NH3 ==

'''Calculation method and basis set: B3LYP/6-31G(d,p)'''

[[File:Gyu_nh3_opt_631g_dp.PNG]]

<pre>Item Value Threshold Converged?
Maximum Force 0.000006 0.000450 YES
RMS Force 0.000004 0.000300 YES
Maximum Displacement 0.000012 0.001800 YES
RMS Displacement 0.000008 0.001200 YES
</pre>

=== Frequency Analysis ===

[[Media:GLYNISYU_NH3_FREQ.LOG|Frequency analysis log file here]]

<pre>Low frequencies --- -8.5646 -8.5588 -0.0041 0.0455 0.1784 26.4183
Low frequencies --- 1089.7603 1694.1865 1694.1865</pre>

<jmol><jmolApplet>
<title>Optimised NH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>GLYNISYU_NH3_FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

== NH3BH3 ==

'''Calculation method and basis set: B3LYP/6-31G(d,p)'''

[[File:Gyu_nh3bh3_opt_631g_dp.PNG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000122 0.000450 YES
RMS Force 0.000058 0.000300 YES
Maximum Displacement 0.000540 0.001800 YES
RMS Displacement 0.000297 0.001200 YES</pre>

=== Frequency Analysis ===

[[Media:GYU_NH3BH3_FREQ.LOG|Frequency analysis log file here]]

<pre>Low frequencies --- -0.0571 -0.0499 -0.0075 21.7150 21.7251 40.6257
Low frequencies --- 266.0444 632.3706 640.1455</pre>

<jmol><jmolApplet>
<title>Optimised NH3BH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>GYU_NH3BH3_FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

=== Calculations ===

{| class="wikitable" border="1"
! Molecule!! Energy (au)
|-
| BH3 || -26.61532
|-
| NH3 || -56.55777
|-
| NH3BH3 || -83.22469
|}

The bond association energy can be calculated using ΔE=E(NH3BH3)-[E(NH3)+E(BH3)].

ΔE = -83.22469-(-26.61532+-56.55777) = -0.0516 au

In kJmol-1, the bond association energy comes out to be -135 kJmol-1

The calculated bond dissociation energy for the B-N dative bond is 135 kJmol-1. Comparison to the bond dissociation energy of a Br-Br bond (192 kJmol-1) indicates that the B-N bond is weak, as the dissociation energy is even smaller than that for Br-Br<ref name="Br_Br"/>.

<references>
<ref name="Br_Br">The bond dissociation energy of Br-Br can be found here [https://en.wikipedia.org/wiki/Bond-dissociation_energy]</ref>/
</references>

== BBr3 ==

'''Calculation method and basis set: B3LYP/6-31G(d,p)'''

[[File:Gyu_bbr3_opt_631g_dp.PNG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000008 0.000450 YES
RMS Force 0.000005 0.000300 YES
Maximum Displacement 0.000036 0.001800 YES
RMS Displacement 0.000023 0.001200 YES</pre>

=== Frequency Analysis ===

[[Media: Gyu_bbr3_freq_server.log|Frequency Analysis log file here]]

<pre> Low frequencies --- -0.0137 -0.0064 -0.0046 2.4315 2.4315 4.8421
Low frequencies --- 155.9631 155.9651 267.7052</pre>

<jmol><jmolApplet>
<title>Optimised BBr3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>Gyu_bbr3_freq_server.log</uploadedFileContents>
</jmolApplet></jmol>

Link to Dspace: http://hdl.handle.net/10042/202448

{{DOI|10042/202448}}

== Project Section: Aromaticity ==

=== Benzene ===

'''Calculation method and basis set: B3LYP/6-31G(d,p)'''

[[File:Gyu_benzene_opt_631g_dp.PNG]]

<pre> Item Value Threshold Converged?
Maximum Force 0.000194 0.000450 YES
RMS Force 0.000077 0.000300 YES
Maximum Displacement 0.000824 0.001800 YES
RMS Displacement 0.000289 0.001200 YES</pre>

==== Frequency Analysis ====

[[Media: GYU_BENZENE_FREQ_631G_DP.LOG|Frequency Analysis log file here]]

<pre>Low frequencies --- -2.1456 -2.1456 -0.0087 -0.0042 -0.0041 10.4835
Low frequencies --- 413.9768 413.9768 621.1390</pre>

<jmol><jmolApplet>
<title>Optimised Benzene molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>GYU_BENZENE_FREQ_631G_DP.LOG</uploadedFileContents>
</jmolApplet></jmol>

=== Borazine ===

'''Calculation method and basis set: B3LYP/6-31G(d,p)'''

[[File:Gyu_borazine_opt_631g_dp.PNG]]

<pre>Item Value Threshold Converged?
Maximum Force 0.000011 0.000450 YES
RMS Force 0.000005 0.000300 YES
Maximum Displacement 0.000065 0.001800 YES
RMS Displacement 0.000021 0.001200 YES</pre>

==== Frequency Analysis ====

[[Media:GYU_BORAZINE_FREQ_631G_DP.LOG|Frequency analysis log file here]]

<pre>Low frequencies --- -13.9554 -13.7954 -10.4509 -0.0104 -0.0091 0.0726
Low frequencies --- 289.0422 289.0509 403.8550</pre>

<jmol><jmolApplet>
<title>Optimised Borazine molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>GYU_BORAZINE_FREQ_631G_DP.LOG</uploadedFileContents>
</jmolApplet></jmol>

=== Benzene vs. Borazine ===

==== Charge Distribution ====

{| class="wikitable" border="1"
! Benzene !! Borazine
|-
| [[File:Gyu_Benzene_1.102_colour.PNG]] || [[File:Gyu_Borazine_1.102_colour.PNG]]
|-
| Carbon Charge: -0.239 || Boron Charge: 0.747
|-
| Hydrogen Charge: 0.239 || Nitrogen Charge: -1.102
|-
| - || Hydrogen Charge (bonded to B): -0.077
|-
| - || Hydrogen Charge (bonded to N): 0.432
|}

In benzene, more electron density is located around the carbon atoms (-0.239) than the hydrogen atoms (0.239). This can be reasoned by comparing their relative electronegativities. Using the Pauling scale, carbon has a higher electronegativity (2.55) than hydrogen (2.20) and the values for the charge distribution of benzene reflects this; carbon has a negative charge distribution whilst hydrogen has a positive one. As benzene is symmetrical, all of the carbon atoms have the same electron distribution around them, as do the hydrogen atoms.

Unlike in benzene, the charge distribution around borazine is not symmetrical. The same argument of electronegativites can be used to explain this. From the elements in borazine, nitrogen has the largest electronegativity (3.04). When looking at the charge distribution of borazine above, the nitrogen atoms have the most negative values (-1.102), and so have the most electron density surrounding them. Boron has an electronegativity of 2.04. These boron atoms are located in between nitrogen atoms, therefore the charge distribution around boron is 0.747 as nitrogen is more electronegative, drawing electron density away from the boron atoms. The hydrogen atoms have different electron density around them, which depends on whether they are bonded to nitrogen or boron. The H atoms attached to boron have a negative value for charge distribution because hydrogen has a larger electronegativity than boron (2.20 to 2.04). The hydrogens attached to nitrogen have a positive charge distribution as nitrogen has a much greater electronegativity than hydrogen (3.04 to 2.20).

==== Molecular Orbital Comparison ====

{| class="wikitable" border="1"
! Benzene MO !! Borazine MO !! Description
|-
| [[File:Gyu_benzene_mo_17.PNG]] || cell || cell
|-
| [[File:Gyu_benzene_mo_13.PNG]] || [[File:Gyu_borazine_mo_16.PNG]] || Benzene MO13, Borazine MO16: Both of these orbitals are σ-antibonding MOs. As benzene has D6h symmetry, the orbital contributions of each carbon and hydrogen is symmetric. However, in borazine the boron atoms have larger lobes since they have a lower electronegativity, contributing more to the antibonding orbitals.
|-
| [[File:Gyu_benzene_homo_21.PNG]] || [[File:Gyu_borazine_homo_21.PNG]] || HOMO MO 21: The HOMO of benzene and borazine are very similar and are both π-bonding MOs. The main difference being that the benzene HOMO is entirely symmetric, whereas the borazine HOMO is skewed due to the difference in electronegativities of boron and nitrogen. Nitrogen has a higher electronegativity so there is a more concentrated area at the nitrogen atom, as it contributes more to the bonding orbital.
|}

Rep:Mod:t3gy216

2018-05-23T16:08:57Z

Gy216: /* Benzene vs. Borazine */

File:Gyu Benzene 1.102 colour.PNG

2018-05-23T16:08:33Z

Gy216: