ChemWiki - User contributions [en]

Rep:Mod:by416

2018-05-25T16:34:44Z

By416: /* IR: */

= '''BH3 Molecule''' =

Method:B3LYP

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

[[File:BY BH3 OPT.png]]

Item Value Threshold Converged?
Maximum Force 0.000070 0.000450 YES
RMS Force 0.000039 0.000300 YES
Maximum Displacement 0.000356 0.001800 YES
RMS Displacement 0.000214 0.001200 YES

Media: [[File:BY416_BH3_FREQ.LOG]]

Low frequencies --- -0.6727 -0.3834 -0.0055 12.9097 16.4795 16.4932
Low frequencies --- 1163.0392 1213.2115 1213.2142

<jmol><jmolApplet>
<title>BH3</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>BY416_BH3_FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

== '''IR''' ==

{| class="wikitable"
|+
|-
|wavenumber (cm-1) || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1164
|92
|A2"
|yes
|out-of-plane bend
|-
|1214
|14
|E'
|slight
|bend
|-
|1214
|14
|E'
|slight
|bend
|-
|2580
|0
|A1'
|no
|symmetric stretch
|-
|2713
|126
|E'
|yes
|asymmetric stretch
|-
|2713
|126
|E'
|yes
|asymmetric stretch
|}

[[File:Bh3 ir by416.png]]

There are 6 vibrations of BH3, as seen in the table. These do not show up in the IR spectrum because there are two pairs which are degenerate (of the same energy). These degenerate pairs are only seen once in the IR spectrum. Furthermore, for a vibration to be IR active it must have a change in the dipole moment. The A1 symmetric stretch does not invlve an overall change in the dipole moment. Therefore it is not seen in the IR spectrum.

== '''MO diagram''' ==

[[File:MOby416.png]]

(MO diagram for BH3, Lecture 4 Tutorial Problem Model Answers, P. Hunt, [http://www.huntresearchgroup.org.uk/teaching/teaching_comp_lab_year2a/Tut_MO_diagram_BH3.pdf], accessed 22/05/18)

The LCAO AOs are similar to the computed MOs. There are areas of electron density and no electron density (nodes) seen in both. This shows that qualitative MO theory is useful as its accuracy is high.

= '''NH3 Molecule''' =

Method:B3LYP

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

[[File:NH3 by416 opt.png]]

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

Media: [[File:BY416 NH3 OPTIMISATION.LOG]]

Low frequencies --- -8.5646 -8.5588 -0.0044 0.0454 0.1784 26.4183
Low frequencies --- 1089.7603 1694.1865 1694.1865

<jmol><jmolApplet>
<title>NH3 molecule</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>BY416 NH3 OPTIMISATION.LOG</uploadedFileContents>
</jmolApplet></jmol>

= '''NH3BH3''' =

Method:B3LYP

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

[[File:NH3BH3 by416 opt2.PNG]]

Item Value Threshold Converged?
Maximum Force 0.000122 0.000450 YES
RMS Force 0.000058 0.000300 YES
Maximum Displacement 0.000513 0.001800 YES
RMS Displacement 0.000296 0.001200 YES

Media: [[File:BY416 NH3BH3 OPT.LOG]]

Low frequencies --- -13.6017 -0.0013 -0.0007 -0.0003 19.4531 43.3457
Low frequencies --- 266.2693 632.1302 638.2535

<jmol><jmolApplet>
<title>NH3BH3 molecule</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>BY416 NH3BH3 OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

== Energy Calculations: ==

E(BH3)= -26.61532364 a.u

E(NH3)= -56.55776873 a.u

E(NH3BH3)= -83.22468893 a.u

Association energy, deltaJ : E(NH3BH3) - [E(NH3)+E(BH3)] = -0.05159656 a.u

-0.05159656 x 2625.5 = -135.4667683 kJ/mol

The energy calculation shows that the B-N bond is weak. The bond enthalpy is +135 kJ/mol. This is lower than other organic bonds.[https://pubs.acs.org/doi/pdf/10.1021/ar020230d]

= '''BBr3''' =

Method:B3LYP

Basis: 6-31G (d,p) for B, LanL2DZ (pseudo-potential) for Br

[[File:Bbr3 opt by4162.PNG]]

Item Value Threshold Converged?
Maximum Force 0.000023 0.000450 YES
RMS Force 0.000014 0.000300 YES
Maximum Displacement 0.000118 0.001800 YES
RMS Displacement 0.000069 0.001200 YES

{{DOI|10042/202469}}

[[File:By416 bbr3 freq3.log]]

Low frequencies --- -3.1706 -0.0002 -0.0001 0.0000 1.6540 3.3467
Low frequencies --- 155.8924 155.9627 267.7046

<jmol><jmolApplet>
<title>BBr3 molecule</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>By416 bbr3 freq3.log</uploadedFileContents>
</jmolApplet></jmol>

= '''Project : Aromaticity''' =

== '''Benzene''' ==

Method:B3LYP

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

[[File:Benzene opt2 by416.PNG]]

Item Value Threshold Converged?
Maximum Force 0.000198 0.000450 YES
RMS Force 0.000082 0.000300 YES
Maximum Displacement 0.000849 0.001800 YES
RMS Displacement 0.000305 0.001200 YES

[[File:BENZENE FREQ BY416.LOG]]

Low frequencies --- -11.6728 -0.0010 -0.0008 0.0003 6.6686 15.6846
Low frequencies --- 414.0392 414.6031 621.0860

<jmol><jmolApplet>
<title>Benzene</title>
<color>black</color>
<size>400</size>
<uploadedFileContents>BENZENE FREQ BY416.LOG</uploadedFileContents>
</jmolApplet></jmol>

=== '''Charge distribution:''' ===

[[File:Benzene chargedist by416 2.PNG]]

'''Charges:'''

Carbon = -0.239

Hydrogen = 0.239

'''Discussion:'''

In benzene, every carbon atom has the same electronegativity, therefore has the same charge. The same applies to the hydrogen atoms. The hydrogen atoms have the same magnitude of charge as carbon, but the opposite sign.

== '''Borazine''' ==

Method:B3LYP

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

[[File:Borazine opt2 by416.PNG]

Item Value Threshold Converged?
Maximum Force 0.000073 0.000450 YES
RMS Force 0.000026 0.000300 YES
Maximum Displacement 0.000298 0.001800 YES
RMS Displacement 0.000106 0.001200 YES

[[File:BORAZINE FREQ2 BY416.LOG]]

Low frequencies --- -15.3480 -15.3480 -12.7393 -0.0158 -0.0107 -0.0107
Low frequencies --- 288.9049 288.9049 403.7235

<jmol><jmolApplet>
<title>Borazine</title>
<color>black</color>
<size>400</size>
<uploadedFileContents>BORAZINE FREQ BY416.LOG</uploadedFileContents>
</jmolApplet></jmol>

==='''Charge distribution:''' ===

[[File:Borazine chargedist by416.PNG]]

Charges:

Nitrogen= -1.102

Hydrogen atoms bonded to Nitrogen= 0.432

Boron= 0.747

Hydrogen atoms bonded to Boron= -0.077

'''Discussion:'''

Nitrogen is much more electronegative than boron and hydrogen. Therefore, it pulls electron density from orbitals of B and H, towards itself. As a result the hydrogen atoms bonded to nitrogen have a positive charge because electron density has been pulled away. On the other hand, boron is less electronegative than nitrogen so does not pull as much electron density towards itself. Therefore, it has a less negative charge and its electron density is dispersed on the hydrogen. Hence the hydrogen atoms bonded to boron are more negative than the hydrogen atoms bonded to nitrogen.

== '''Charge Comparison''' ==

Borazine has N - H bonds which are more polar than benzene and B - H bonds which are less polar than benzene. This is because nitrogen is more electronegative than carbon. Hence creating bonds with a greater charge difference/ more polar. Boron is less electronegative than carbon therefore there is lower charge difference between B-H than C-H.

== '''MO Comparisons''' ==

'''1.'''

Benzene:
[[File:Benzene mo 2 by416.PNG]]]

Borazine:
[[File:Borazine MO 2 by416.PNG]]

These MO diagrams represent p orbitals. 3 p orbitals are in the same phase on either side (the grouping of electron density). The phases are distinguished by colour. In between the areas of electron density, there are nodes where the likelihood of finding an electron is 0. For benzene, the electron density is distributed evenly among the p orbtials in the same phase. This is because all the carbons in benzene are of the same electronegativity. However, for borazine, the electron distribution is gravitated towards the nitrogen atoms (blue atoms). This is because nitrogen is much more electronegative than boron, as discussed before when considering charge density.

'''2.'''

Benzene:
[[File:Benzene mo 3 by416.PNG]]

Borazine:
[[File:Borazine mo 3 by416.PNG]]

This example is also looking at p orbitals. As mentioned in the other examples, the distribution is more equal in benzene than borazine. In borazine, the orbitals are skewed because of the different electronegativities. The distribution is even in benzene because the electronegativies are the same.

'''3.'''

Benzene:
[[File:Benzene mo 4 by416.PNG]]

Borazine:
[[File:Borazine mo 4 by416.PNG]]

This example also looks at P orbitals, here all the p orbitals are in the same phase. Only the above place is showing in the pictures, there is also an orbital underneath. The image was taken like this to see the distribution of one orbital. In this case the electron density is distributed equally among the benzene. This is because of the equal electronegativty of the carbons. In borazine, however, the spread of electron density is less equal. The nitrogen atoms have more electron density surrounding them, because of their higher electronegativity.

== '''Aromaticity''' ==

For a molecule to be aromatic it needs to obey certain rules. These rules include: being cyclic, planar. all the atoms being conjugated and obeying the 4n+2 rule. The 4n+2 rule, also known as huckle's rule, states that for a molecule to be aromatic it must have the right number of pi electrons. This right number is 4n+2, which is the mathematical shorthand for the series: 2,6,10,14,18... where n must be an integer. Therefore, for the molecule to be aromatic it must have pi electrons that equal to a number in that series. For example, even though clyclooctatetraene is cyclic, conjugated and planar it is not aromatic as it has 8 pi electrons.

The basic conceptions of aromaticity are a simplified version of the MOs. For example, the idea of conjugation is rigid as it assigns electrons to certain bonds. However, as shown in the MO diagrams, the electrons can be found anywhere in the orbital. Furthermore, the idea of aromaticity originated from benzene. The rules assigned, also based from benzene/aromatic compounds, do not apply in some cases. For example benzene is not planar in certain conditions. The idea of aromaticity can also be applied to compounds which are not the conventional aromatic compounds. Some examples include polyhedral boranes, metallobenzenes and fullerenes.

The Pz orbitals are not conjugated in the pi system therefore they cannot be considered when looking at aromaticity. The orbitals are not conjugated because their orientation/angle is not at the correction orientation to allow the pi orbitals to create a conjugated system. Therefore, it is not a good description for aromaticity.

[https://onlinelibrary.wiley.com/doi/epdf/10.1002/chem.200700250]

Rep:Mod:by416

2018-05-25T16:34:30Z

By416:

= '''BH3 Molecule''' =

Method:B3LYP

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

[[File:BY BH3 OPT.png]]

Item Value Threshold Converged?
Maximum Force 0.000070 0.000450 YES
RMS Force 0.000039 0.000300 YES
Maximum Displacement 0.000356 0.001800 YES
RMS Displacement 0.000214 0.001200 YES

Media: [[File:BY416_BH3_FREQ.LOG]]

Low frequencies --- -0.6727 -0.3834 -0.0055 12.9097 16.4795 16.4932
Low frequencies --- 1163.0392 1213.2115 1213.2142

<jmol><jmolApplet>
<title>BH3</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>BY416_BH3_FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

== '''IR:''' ==

{| class="wikitable"
|+
|-
|wavenumber (cm-1) || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1164
|92
|A2"
|yes
|out-of-plane bend
|-
|1214
|14
|E'
|slight
|bend
|-
|1214
|14
|E'
|slight
|bend
|-
|2580
|0
|A1'
|no
|symmetric stretch
|-
|2713
|126
|E'
|yes
|asymmetric stretch
|-
|2713
|126
|E'
|yes
|asymmetric stretch
|}

[[File:Bh3 ir by416.png]]

There are 6 vibrations of BH3, as seen in the table. These do not show up in the IR spectrum because there are two pairs which are degenerate (of the same energy). These degenerate pairs are only seen once in the IR spectrum. Furthermore, for a vibration to be IR active it must have a change in the dipole moment. The A1 symmetric stretch does not invlve an overall change in the dipole moment. Therefore it is not seen in the IR spectrum.

== '''MO diagram''' ==

[[File:MOby416.png]]

(MO diagram for BH3, Lecture 4 Tutorial Problem Model Answers, P. Hunt, [http://www.huntresearchgroup.org.uk/teaching/teaching_comp_lab_year2a/Tut_MO_diagram_BH3.pdf], accessed 22/05/18)

The LCAO AOs are similar to the computed MOs. There are areas of electron density and no electron density (nodes) seen in both. This shows that qualitative MO theory is useful as its accuracy is high.

= '''NH3 Molecule''' =

Method:B3LYP

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

[[File:NH3 by416 opt.png]]

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

Media: [[File:BY416 NH3 OPTIMISATION.LOG]]

Low frequencies --- -8.5646 -8.5588 -0.0044 0.0454 0.1784 26.4183
Low frequencies --- 1089.7603 1694.1865 1694.1865

<jmol><jmolApplet>
<title>NH3 molecule</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>BY416 NH3 OPTIMISATION.LOG</uploadedFileContents>
</jmolApplet></jmol>

= '''NH3BH3''' =

Method:B3LYP

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

[[File:NH3BH3 by416 opt2.PNG]]

Item Value Threshold Converged?
Maximum Force 0.000122 0.000450 YES
RMS Force 0.000058 0.000300 YES
Maximum Displacement 0.000513 0.001800 YES
RMS Displacement 0.000296 0.001200 YES

Media: [[File:BY416 NH3BH3 OPT.LOG]]

Low frequencies --- -13.6017 -0.0013 -0.0007 -0.0003 19.4531 43.3457
Low frequencies --- 266.2693 632.1302 638.2535

<jmol><jmolApplet>
<title>NH3BH3 molecule</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>BY416 NH3BH3 OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

== Energy Calculations: ==

E(BH3)= -26.61532364 a.u

E(NH3)= -56.55776873 a.u

E(NH3BH3)= -83.22468893 a.u

Association energy, deltaJ : E(NH3BH3) - [E(NH3)+E(BH3)] = -0.05159656 a.u

-0.05159656 x 2625.5 = -135.4667683 kJ/mol

The energy calculation shows that the B-N bond is weak. The bond enthalpy is +135 kJ/mol. This is lower than other organic bonds.[https://pubs.acs.org/doi/pdf/10.1021/ar020230d]

= '''BBr3''' =

Method:B3LYP

Basis: 6-31G (d,p) for B, LanL2DZ (pseudo-potential) for Br

[[File:Bbr3 opt by4162.PNG]]

Item Value Threshold Converged?
Maximum Force 0.000023 0.000450 YES
RMS Force 0.000014 0.000300 YES
Maximum Displacement 0.000118 0.001800 YES
RMS Displacement 0.000069 0.001200 YES

{{DOI|10042/202469}}

[[File:By416 bbr3 freq3.log]]

Low frequencies --- -3.1706 -0.0002 -0.0001 0.0000 1.6540 3.3467
Low frequencies --- 155.8924 155.9627 267.7046

<jmol><jmolApplet>
<title>BBr3 molecule</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>By416 bbr3 freq3.log</uploadedFileContents>
</jmolApplet></jmol>

= '''Project : Aromaticity''' =

== '''Benzene''' ==

Method:B3LYP

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

[[File:Benzene opt2 by416.PNG]]

Item Value Threshold Converged?
Maximum Force 0.000198 0.000450 YES
RMS Force 0.000082 0.000300 YES
Maximum Displacement 0.000849 0.001800 YES
RMS Displacement 0.000305 0.001200 YES

[[File:BENZENE FREQ BY416.LOG]]

Low frequencies --- -11.6728 -0.0010 -0.0008 0.0003 6.6686 15.6846
Low frequencies --- 414.0392 414.6031 621.0860

<jmol><jmolApplet>
<title>Benzene</title>
<color>black</color>
<size>400</size>
<uploadedFileContents>BENZENE FREQ BY416.LOG</uploadedFileContents>
</jmolApplet></jmol>

=== '''Charge distribution:''' ===

[[File:Benzene chargedist by416 2.PNG]]

'''Charges:'''

Carbon = -0.239

Hydrogen = 0.239

'''Discussion:'''

In benzene, every carbon atom has the same electronegativity, therefore has the same charge. The same applies to the hydrogen atoms. The hydrogen atoms have the same magnitude of charge as carbon, but the opposite sign.

== '''Borazine''' ==

Method:B3LYP

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

[[File:Borazine opt2 by416.PNG]

Item Value Threshold Converged?
Maximum Force 0.000073 0.000450 YES
RMS Force 0.000026 0.000300 YES
Maximum Displacement 0.000298 0.001800 YES
RMS Displacement 0.000106 0.001200 YES

[[File:BORAZINE FREQ2 BY416.LOG]]

Low frequencies --- -15.3480 -15.3480 -12.7393 -0.0158 -0.0107 -0.0107
Low frequencies --- 288.9049 288.9049 403.7235

<jmol><jmolApplet>
<title>Borazine</title>
<color>black</color>
<size>400</size>
<uploadedFileContents>BORAZINE FREQ BY416.LOG</uploadedFileContents>
</jmolApplet></jmol>

==='''Charge distribution:''' ===

[[File:Borazine chargedist by416.PNG]]

Charges:

Nitrogen= -1.102

Hydrogen atoms bonded to Nitrogen= 0.432

Boron= 0.747

Hydrogen atoms bonded to Boron= -0.077

'''Discussion:'''

Nitrogen is much more electronegative than boron and hydrogen. Therefore, it pulls electron density from orbitals of B and H, towards itself. As a result the hydrogen atoms bonded to nitrogen have a positive charge because electron density has been pulled away. On the other hand, boron is less electronegative than nitrogen so does not pull as much electron density towards itself. Therefore, it has a less negative charge and its electron density is dispersed on the hydrogen. Hence the hydrogen atoms bonded to boron are more negative than the hydrogen atoms bonded to nitrogen.

== '''Charge Comparison''' ==

Borazine has N - H bonds which are more polar than benzene and B - H bonds which are less polar than benzene. This is because nitrogen is more electronegative than carbon. Hence creating bonds with a greater charge difference/ more polar. Boron is less electronegative than carbon therefore there is lower charge difference between B-H than C-H.

== '''MO Comparisons''' ==

'''1.'''

Benzene:
[[File:Benzene mo 2 by416.PNG]]]

Borazine:
[[File:Borazine MO 2 by416.PNG]]

These MO diagrams represent p orbitals. 3 p orbitals are in the same phase on either side (the grouping of electron density). The phases are distinguished by colour. In between the areas of electron density, there are nodes where the likelihood of finding an electron is 0. For benzene, the electron density is distributed evenly among the p orbtials in the same phase. This is because all the carbons in benzene are of the same electronegativity. However, for borazine, the electron distribution is gravitated towards the nitrogen atoms (blue atoms). This is because nitrogen is much more electronegative than boron, as discussed before when considering charge density.

'''2.'''

Benzene:
[[File:Benzene mo 3 by416.PNG]]

Borazine:
[[File:Borazine mo 3 by416.PNG]]

This example is also looking at p orbitals. As mentioned in the other examples, the distribution is more equal in benzene than borazine. In borazine, the orbitals are skewed because of the different electronegativities. The distribution is even in benzene because the electronegativies are the same.

'''3.'''

Benzene:
[[File:Benzene mo 4 by416.PNG]]

Borazine:
[[File:Borazine mo 4 by416.PNG]]

This example also looks at P orbitals, here all the p orbitals are in the same phase. Only the above place is showing in the pictures, there is also an orbital underneath. The image was taken like this to see the distribution of one orbital. In this case the electron density is distributed equally among the benzene. This is because of the equal electronegativty of the carbons. In borazine, however, the spread of electron density is less equal. The nitrogen atoms have more electron density surrounding them, because of their higher electronegativity.

== '''Aromaticity''' ==

For a molecule to be aromatic it needs to obey certain rules. These rules include: being cyclic, planar. all the atoms being conjugated and obeying the 4n+2 rule. The 4n+2 rule, also known as huckle's rule, states that for a molecule to be aromatic it must have the right number of pi electrons. This right number is 4n+2, which is the mathematical shorthand for the series: 2,6,10,14,18... where n must be an integer. Therefore, for the molecule to be aromatic it must have pi electrons that equal to a number in that series. For example, even though clyclooctatetraene is cyclic, conjugated and planar it is not aromatic as it has 8 pi electrons.

The basic conceptions of aromaticity are a simplified version of the MOs. For example, the idea of conjugation is rigid as it assigns electrons to certain bonds. However, as shown in the MO diagrams, the electrons can be found anywhere in the orbital. Furthermore, the idea of aromaticity originated from benzene. The rules assigned, also based from benzene/aromatic compounds, do not apply in some cases. For example benzene is not planar in certain conditions. The idea of aromaticity can also be applied to compounds which are not the conventional aromatic compounds. Some examples include polyhedral boranes, metallobenzenes and fullerenes.

The Pz orbitals are not conjugated in the pi system therefore they cannot be considered when looking at aromaticity. The orbitals are not conjugated because their orientation/angle is not at the correction orientation to allow the pi orbitals to create a conjugated system. Therefore, it is not a good description for aromaticity.

[https://onlinelibrary.wiley.com/doi/epdf/10.1002/chem.200700250]

Rep:Mod:by416

2018-05-25T16:33:10Z

By416:

= '''BH3 Molecule''' =

Method:B3LYP

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

[[File:BY BH3 OPT.png]]

Item Value Threshold Converged?
Maximum Force 0.000070 0.000450 YES
RMS Force 0.000039 0.000300 YES
Maximum Displacement 0.000356 0.001800 YES
RMS Displacement 0.000214 0.001200 YES

Media: [[File:BY416_BH3_FREQ.LOG]]

Low frequencies --- -0.6727 -0.3834 -0.0055 12.9097 16.4795 16.4932
Low frequencies --- 1163.0392 1213.2115 1213.2142

<jmol><jmolApplet>
<title>BH3</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>BY416_BH3_FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

'''IR:'''

{| class="wikitable"
|+
|-
|wavenumber (cm-1) || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1164
|92
|A2"
|yes
|out-of-plane bend
|-
|1214
|14
|E'
|slight
|bend
|-
|1214
|14
|E'
|slight
|bend
|-
|2580
|0
|A1'
|no
|symmetric stretch
|-
|2713
|126
|E'
|yes
|asymmetric stretch
|-
|2713
|126
|E'
|yes
|asymmetric stretch
|}

[[File:Bh3 ir by416.png]]

There are 6 vibrations of BH3, as seen in the table. These do not show up in the IR spectrum because there are two pairs which are degenerate (of the same energy). These degenerate pairs are only seen once in the IR spectrum. Furthermore, for a vibration to be IR active it must have a change in the dipole moment. The A1 symmetric stretch does not invlve an overall change in the dipole moment. Therefore it is not seen in the IR spectrum.

'''MO diagram'''
[[File:MOby416.png]]

(MO diagram for BH3, Lecture 4 Tutorial Problem Model Answers, P. Hunt, [http://www.huntresearchgroup.org.uk/teaching/teaching_comp_lab_year2a/Tut_MO_diagram_BH3.pdf], accessed 22/05/18)

The LCAO AOs are similar to the computed MOs. There are areas of electron density and no electron density (nodes) seen in both. This shows that qualitative MO theory is useful as its accuracy is high.

= '''NH3 Molecule''' =

Method:B3LYP

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

[[File:NH3 by416 opt.png]]

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

Media: [[File:BY416 NH3 OPTIMISATION.LOG]]

Low frequencies --- -8.5646 -8.5588 -0.0044 0.0454 0.1784 26.4183
Low frequencies --- 1089.7603 1694.1865 1694.1865

<jmol><jmolApplet>
<title>NH3 molecule</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>BY416 NH3 OPTIMISATION.LOG</uploadedFileContents>
</jmolApplet></jmol>

= '''NH3BH3''' =

Method:B3LYP

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

[[File:NH3BH3 by416 opt2.PNG]]

Item Value Threshold Converged?
Maximum Force 0.000122 0.000450 YES
RMS Force 0.000058 0.000300 YES
Maximum Displacement 0.000513 0.001800 YES
RMS Displacement 0.000296 0.001200 YES

Media: [[File:BY416 NH3BH3 OPT.LOG]]

Low frequencies --- -13.6017 -0.0013 -0.0007 -0.0003 19.4531 43.3457
Low frequencies --- 266.2693 632.1302 638.2535

<jmol><jmolApplet>
<title>NH3BH3 molecule</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>BY416 NH3BH3 OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

Energy Calculations:

E(BH3)= -26.61532364 a.u

E(NH3)= -56.55776873 a.u

E(NH3BH3)= -83.22468893 a.u

Association energy, deltaJ : E(NH3BH3) - [E(NH3)+E(BH3)] = -0.05159656 a.u

-0.05159656 x 2625.5 = -135.4667683 kJ/mol

The energy calculation shows that the B-N bond is weak. The bond enthalpy is +135 kJ/mol. This is lower than other organic bonds.[https://pubs.acs.org/doi/pdf/10.1021/ar020230d]

= '''BBr3''' =

Method:B3LYP

Basis: 6-31G (d,p) for B, LanL2DZ (pseudo-potential) for Br

[[File:Bbr3 opt by4162.PNG]]

Item Value Threshold Converged?
Maximum Force 0.000023 0.000450 YES
RMS Force 0.000014 0.000300 YES
Maximum Displacement 0.000118 0.001800 YES
RMS Displacement 0.000069 0.001200 YES

{{DOI|10042/202469}}

[[File:By416 bbr3 freq3.log]]

Low frequencies --- -3.1706 -0.0002 -0.0001 0.0000 1.6540 3.3467
Low frequencies --- 155.8924 155.9627 267.7046

<jmol><jmolApplet>
<title>BBr3 molecule</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>By416 bbr3 freq3.log</uploadedFileContents>
</jmolApplet></jmol>

= '''Project : Aromaticity''' =

== '''Benzene''' ==

Method:B3LYP

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

[[File:Benzene opt2 by416.PNG]]

Item Value Threshold Converged?
Maximum Force 0.000198 0.000450 YES
RMS Force 0.000082 0.000300 YES
Maximum Displacement 0.000849 0.001800 YES
RMS Displacement 0.000305 0.001200 YES

[[File:BENZENE FREQ BY416.LOG]]

Low frequencies --- -11.6728 -0.0010 -0.0008 0.0003 6.6686 15.6846
Low frequencies --- 414.0392 414.6031 621.0860

<jmol><jmolApplet>
<title>Benzene</title>
<color>black</color>
<size>400</size>
<uploadedFileContents>BENZENE FREQ BY416.LOG</uploadedFileContents>
</jmolApplet></jmol>

=== '''Charge distribution:''' ===

[[File:Benzene chargedist by416 2.PNG]]

Charges:

Carbon = -0.239

Hydrogen = 0.239

Discussion:

In benzene, every carbon atom has the same electronegativity, therefore has the same charge. The same applies to the hydrogen atoms. The hydrogen atoms have the same magnitude of charge as carbon, but the opposite sign.

== '''Borazine''' ==

Method:B3LYP

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

[[File:Borazine opt2 by416.PNG]

Item Value Threshold Converged?
Maximum Force 0.000073 0.000450 YES
RMS Force 0.000026 0.000300 YES
Maximum Displacement 0.000298 0.001800 YES
RMS Displacement 0.000106 0.001200 YES

[[File:BORAZINE FREQ2 BY416.LOG]]

Low frequencies --- -15.3480 -15.3480 -12.7393 -0.0158 -0.0107 -0.0107
Low frequencies --- 288.9049 288.9049 403.7235

<jmol><jmolApplet>
<title>Borazine</title>
<color>black</color>
<size>400</size>
<uploadedFileContents>BORAZINE FREQ BY416.LOG</uploadedFileContents>
</jmolApplet></jmol>

==='''Charge distribution:''' ===

[[File:Borazine chargedist by416.PNG]]

Charges:

Nitrogen= -1.102

Hydrogen atoms bonded to Nitrogen= 0.432

Boron= 0.747

Hydrogen atoms bonded to Boron= -0.077

Discussion:

Nitrogen is much more electronegative than boron and hydrogen. Therefore, it pulls electron density from orbitals of B and H, towards itself. As a result the hydrogen atoms bonded to nitrogen have a positive charge because electron density has been pulled away. On the other hand, boron is less electronegative than nitrogen so does not pull as much electron density towards itself. Therefore, it has a less negative charge and its electron density is dispersed on the hydrogen. Hence the hydrogen atoms bonded to boron are more negative than the hydrogen atoms bonded to nitrogen.

== '''Charge Comparison''' ==

Borazine has N - H bonds which are more polar than benzene and B - H bonds which are less polar than benzene. This is because nitrogen is more electronegative than carbon. Hence creating bonds with a greater charge difference/ more polar. Boron is less electronegative than carbon therefore there is lower charge difference between B-H than C-H.

== '''MO Comparisons''' ==

'''1.'''

Benzene:
[[File:Benzene mo 2 by416.PNG]]]

Borazine:
[[File:Borazine MO 2 by416.PNG]]

These MO diagrams represent p orbitals. 3 p orbitals are in the same phase on either side (the grouping of electron density). The phases are distinguished by colour. In between the areas of electron density, there are nodes where the likelihood of finding an electron is 0. For benzene, the electron density is distributed evenly among the p orbtials in the same phase. This is because all the carbons in benzene are of the same electronegativity. However, for borazine, the electron distribution is gravitated towards the nitrogen atoms (blue atoms). This is because nitrogen is much more electronegative than boron, as discussed before when considering charge density.

'''2.'''

Benzene:
[[File:Benzene mo 3 by416.PNG]]

Borazine:
[[File:Borazine mo 3 by416.PNG]]

This example is also looking at p orbitals. As mentioned in the other examples, the distribution is more equal in benzene than borazine. In borazine, the orbitals are skewed because of the different electronegativities. The distribution is even in benzene because the electronegativies are the same.

'''3.'''

Benzene:
[[File:Benzene mo 4 by416.PNG]]

Borazine:
[[File:Borazine mo 4 by416.PNG]]

This example also looks at P orbitals, here all the p orbitals are in the same phase. Only the above place is showing in the pictures, there is also an orbital underneath. The image was taken like this to see the distribution of one orbital. In this case the electron density is distributed equally among the benzene. This is because of the equal electronegativty of the carbons. In borazine, however, the spread of electron density is less equal. The nitrogen atoms have more electron density surrounding them, because of their higher electronegativity.

== '''Aromaticity''' ==

For a molecule to be aromatic it needs to obey certain rules. These rules include: being cyclic, planar. all the atoms being conjugated and obeying the 4n+2 rule. The 4n+2 rule, also known as huckle's rule, states that for a molecule to be aromatic it must have the right number of pi electrons. This right number is 4n+2, which is the mathematical shorthand for the series: 2,6,10,14,18... where n must be an integer. Therefore, for the molecule to be aromatic it must have pi electrons that equal to a number in that series. For example, even though clyclooctatetraene is cyclic, conjugated and planar it is not aromatic as it has 8 pi electrons.

The basic conceptions of aromaticity are a simplified version of the MOs. For example, the idea of conjugation is rigid as it assigns electrons to certain bonds. However, as shown in the MO diagrams, the electrons can be found anywhere in the orbital. Furthermore, the idea of aromaticity originated from benzene. The rules assigned, also based from benzene/aromatic compounds, do not apply in some cases. For example benzene is not planar in certain conditions. The idea of aromaticity can also be applied to compounds which are not the conventional aromatic compounds. Some examples include polyhedral boranes, metallobenzenes and fullerenes.

The Pz orbitals are not conjugated in the pi system therefore they cannot be considered when looking at aromaticity. The orbitals are not conjugated because their orientation/angle is not at the correction orientation to allow the pi orbitals to create a conjugated system. Therefore, it is not a good description for aromaticity.

[https://onlinelibrary.wiley.com/doi/epdf/10.1002/chem.200700250]

2018-05-25T15:17:11Z

By416:

Rep:Mod:by416

2018-05-25T15:07:18Z

By416: /* BH3 Molecule */

==== '''BH3 Molecule''' ====
Method:B3LYP

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

[[File:BY BH3 OPT.png]]

Item Value Threshold Converged?
Maximum Force 0.000070 0.000450 YES
RMS Force 0.000039 0.000300 YES
Maximum Displacement 0.000356 0.001800 YES
RMS Displacement 0.000214 0.001200 YES

Media: [[File:BY416_BH3_FREQ.LOG]]

Low frequencies --- -0.6727 -0.3834 -0.0055 12.9097 16.4795 16.4932
Low frequencies --- 1163.0392 1213.2115 1213.2142

<jmol><jmolApplet>
<title>BH3</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>BY416_BH3_FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

'''IR:'''

{| class="wikitable"
|+
|-
|wavenumber (cm-1) || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1164
|92
|A2"
|yes
|out-of-plane bend
|-
|1214
|14
|E'
|slight
|bend
|-
|1214
|14
|E'
|slight
|bend
|-
|2580
|0
|A1'
|no
|symmetric stretch
|-
|2713
|126
|E'
|yes
|asymmetric stretch
|-
|2713
|126
|E'
|yes
|asymmetric stretch
|}

[[File:Bh3 ir by416.png]]

•In your wiki explain why are there less than six peaks in the spectrum, when there are obviously six vibrations.

'''MO diagram'''
[[File:MOby416.png]]

(MO diagram for BH3, Lecture 4 Tutorial Problem Model Answers, P. Hunt, [http://www.huntresearchgroup.org.uk/teaching/teaching_comp_lab_year2a/Tut_MO_diagram_BH3.pdf], accessed 22/05/18)

•Are there any significant differences between the real and LCAO MOs?
•What does this say about the accuracy and usefulness of qualitative MO theory?

'''NH3 Molecule'''

Method:B3LYP

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

[[File:NH3 by416 opt.png]]

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

Media: [[File:BY416 NH3 OPTIMISATION.LOG]]

Low frequencies --- -8.5646 -8.5588 -0.0044 0.0454 0.1784 26.4183
Low frequencies --- 1089.7603 1694.1865 1694.1865

<jmol><jmolApplet>
<title>NH3 molecule</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>BY416 NH3 OPTIMISATION.LOG</uploadedFileContents>
</jmolApplet></jmol>

'''NH3BH3'''

Method:B3LYP

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

[[File:NH3BH3 by416 opt.png]]

Item Value Threshold Converged?
Maximum Force 0.000122 0.000450 YES
RMS Force 0.000058 0.000300 YES
Maximum Displacement 0.000513 0.001800 YES
RMS Displacement 0.000296 0.001200 YES

Media: [[File:BY416 NH3BH3 OPT.LOG]]

Low frequencies --- -13.6017 -0.0013 -0.0007 -0.0003 19.4531 43.3457
Low frequencies --- 266.2693 632.1302 638.2535

<jmol><jmolApplet>
<title>NH3BH3 molecule</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>BY416 NH3BH3 OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

Energy Calculations:

E(BH3)= -26.61532364 a.u

E(NH3)= -56.55776873 a.u

E(NH3BH3)= -83.22468893 a.u

Association energy, deltaJ : E(NH3BH3) - [E(NH3)+E(BH3)] = -0.05159656 a.u

-0.05159656 x 2625.5 = -135.4667683 kJ/mol

So look at your number, is it a sensible value? How do you know what a sensible value is? (Hint: this is a bond energy, so what "ballpark" value should it have?)
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?

'''BBr3'''
Method:B3LYP

Basis: 6-31G (d,p) for B, LanL2DZ (pseudo-potential) for Br

[[File:Bbr3 opt by416.png]]

Item Value Threshold Converged?
Maximum Force 0.000023 0.000450 YES
RMS Force 0.000014 0.000300 YES
Maximum Displacement 0.000118 0.001800 YES
RMS Displacement 0.000069 0.001200 YES

{{DOI|10042/202469}}

[[File:By416 bbr3 freq3.log]]

Low frequencies --- -3.1706 -0.0002 -0.0001 0.0000 1.6540 3.3467
Low frequencies --- 155.8924 155.9627 267.7046

<jmol><jmolApplet>
<title>BBr3 molecule</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>By416 bbr3 freq3.log</uploadedFileContents>
</jmolApplet></jmol>

'''Project'''

'''Aromaticity'''

'''Benzene'''

Method:B3LYP

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

[[File:Benzene opt2 by416.PNG]]

Item Value Threshold Converged?
Maximum Force 0.000198 0.000450 YES
RMS Force 0.000082 0.000300 YES
Maximum Displacement 0.000849 0.001800 YES
RMS Displacement 0.000305 0.001200 YES

[[File:BENZENE FREQ BY416.LOG]]

Low frequencies --- -11.6728 -0.0010 -0.0008 0.0003 6.6686 15.6846
Low frequencies --- 414.0392 414.6031 621.0860

<jmol><jmolApplet>
<title>Benzene</title>
<color>black</color>
<size>400</size>
<uploadedFileContents>BENZENE FREQ BY416.LOG</uploadedFileContents>
</jmolApplet></jmol>

'''Charge distribution:'''

[[File:Benzene chargedist by416 2.PNG]]

Charges:
Carbon = -0.239
Hydrogen = 0.239

Discussion:

In benzene, every carbon atom has the same electronegativity, therefore has the same charge. The same applies to the hydrogen atoms. The hydrogen atoms have the same magnitude of charge as carbon, but the opposite sign.

'''Borazine'''

Method:B3LYP

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

[[File:Borazine opt2 by416.PNG]

Item Value Threshold Converged?
Maximum Force 0.000073 0.000450 YES
RMS Force 0.000026 0.000300 YES
Maximum Displacement 0.000298 0.001800 YES
RMS Displacement 0.000106 0.001200 YES

[[File:BORAZINE FREQ2 BY416.LOG]]

Low frequencies --- -15.3480 -15.3480 -12.7393 -0.0158 -0.0107 -0.0107
Low frequencies --- 288.9049 288.9049 403.7235

<jmol><jmolApplet>
<title>Borazine</title>
<color>black</color>
<size>400</size>
<uploadedFileContents>BORAZINE FREQ BY416.LOG</uploadedFileContents>
</jmolApplet></jmol>

'''Charge distribution:'''

[[File:Borazine chargedist by416.PNG]]

Charges:

Nitrogen= -1.102
Hydrogen atoms bonded to Nitrogen= 0.432
Boron= 0.747
Hydrogen atoms bonded to Boron= -0.077

Discussion:

Nitrogen is much more electronegative than boron and hydrogen. Therefore, it pulls electron density from orbitals of B and H, towards itself. As a result the hydrogen atoms bonded to nitrogen have a positive charge because electron density has been pulled away. On the other hand, boron is less electronegative than nitrogen so does not pull as much electron density towards itself. Therefore, it has a less negative charge and its electron density is dispersed on the hydrogen. Hence the hydrogen atoms bonded to boron are more negative than the hydrogen atoms bonded to nitrogen.

'''Charge Comparison'''

Borazine has N - H bonds which are more polar than benzene and B - H bonds which are less polar than benzene. This is because nitrogen is more electronegative than carbon. Hence creating bonds with a greater charge difference/ more polar. Boron is less electronegative than carbon therefore there is lower charge difference between B-H than C-H.

'''MO Comparisons'''

'''1.'''

Benzene:
[[File:Benzene mo 2 by416.PNG]]]

Borazine:
[[File:Borazine MO 2 by416.PNG]]

These MO diagrams represent p orbitals. 3 p orbitals are in the same phase on either side (the grouping of electron density). The phases are distinguished by colour. In between the areas of electron density, there are nodes where the likelihood of finding an electron is 0. For benzene, the electron density is distributed evenly among the p orbtials in the same phase. This is because all the carbons in benzene are of the same electronegativity. However, for borazine, the electron distribution is gravitated towards the nitrogen atoms (blue atoms). This is because nitrogen is much more electronegative than boron, as discussed before when considering charge density.

'''2.'''

Benzene:
[[File:Benzene mo 3 by416.PNG]]

Borazine:
[[File:Borazine mo 3 by416.PNG]]

This example is also looking at p orbitals.

'''3.'''

Benzene:
[[File:Benzene mo 4 by416.PNG]]

Borazine:
[[File:Borazine mo 4 by416.PNG]]

This example also looks at P orbitals, here all the p orbitals are in the same phase. Only the above place is showing in the pictures, there is also an orbital underneath. The image was taken like this to see the distribution of one orbital. In this case the electron density is distributed equally among the benzene. This is because of the equal electronegativty of the carbons. In borazine, however, the spread of electron density is less equal. The nitrogen atoms have more electron density surrounding them, because of their higher electronegativity.

'''Aromaticity'''

Rep:Mod:by416

2018-05-25T14:45:40Z

By416: /* BH3 Molecule */

==== '''BH3 Molecule''' ====
Method:B3LYP

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

[[File:BY BH3 OPT.png]]

Item Value Threshold Converged?
Maximum Force 0.000070 0.000450 YES
RMS Force 0.000039 0.000300 YES
Maximum Displacement 0.000356 0.001800 YES
RMS Displacement 0.000214 0.001200 YES

Media: [[File:BY416_BH3_FREQ.LOG]]

Low frequencies --- -0.6727 -0.3834 -0.0055 12.9097 16.4795 16.4932
Low frequencies --- 1163.0392 1213.2115 1213.2142

<jmol><jmolApplet>
<title>BH3</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>BY416_BH3_FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

'''IR:'''

{| class="wikitable"
|+
|-
|wavenumber (cm-1) || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1164
|92
|A2"
|yes
|out-of-plane bend
|-
|1214
|14
|E'
|slight
|bend
|-
|1214
|14
|E'
|slight
|bend
|-
|2580
|0
|A1'
|no
|symmetric stretch
|-
|2713
|126
|E'
|yes
|asymmetric stretch
|-
|2713
|126
|E'
|yes
|asymmetric stretch
|}

[[File:Bh3 ir by416.png]]

•In your wiki explain why are there less than six peaks in the spectrum, when there are obviously six vibrations.

'''MO diagram'''
[[File:MOby416.png]]

(MO diagram for BH3, Lecture 4 Tutorial Problem Model Answers, P. Hunt, [http://www.huntresearchgroup.org.uk/teaching/teaching_comp_lab_year2a/Tut_MO_diagram_BH3.pdf], accessed 22/05/18)

•Are there any significant differences between the real and LCAO MOs?
•What does this say about the accuracy and usefulness of qualitative MO theory?

'''NH3 Molecule'''

Method:B3LYP

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

[[File:NH3 by416 opt.png]]

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

Media: [[File:BY416 NH3 OPTIMISATION.LOG]]

Low frequencies --- -8.5646 -8.5588 -0.0044 0.0454 0.1784 26.4183
Low frequencies --- 1089.7603 1694.1865 1694.1865

<jmol><jmolApplet>
<title>NH3 molecule</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>BY416 NH3 OPTIMISATION.LOG</uploadedFileContents>
</jmolApplet></jmol>

'''NH3BH3'''

Method:B3LYP

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

[[File:NH3BH3 by416 opt.png]]

Item Value Threshold Converged?
Maximum Force 0.000122 0.000450 YES
RMS Force 0.000058 0.000300 YES
Maximum Displacement 0.000513 0.001800 YES
RMS Displacement 0.000296 0.001200 YES

Media: [[File:BY416 NH3BH3 OPT.LOG]]

Low frequencies --- -13.6017 -0.0013 -0.0007 -0.0003 19.4531 43.3457
Low frequencies --- 266.2693 632.1302 638.2535

<jmol><jmolApplet>
<title>NH3BH3 molecule</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>BY416 NH3BH3 OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

Energy Calculations:

E(BH3)= -26.61532364 a.u

E(NH3)= -56.55776873 a.u

E(NH3BH3)= -83.22468893 a.u

Association energy, deltaJ : E(NH3BH3) - [E(NH3)+E(BH3)] = -0.05159656 a.u

-0.05159656 x 2625.5 = -135.4667683 kJ/mol

So look at your number, is it a sensible value? How do you know what a sensible value is? (Hint: this is a bond energy, so what "ballpark" value should it have?)
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?

'''BBr3'''
Method:B3LYP

Basis: 6-31G (d,p) for B, LanL2DZ (pseudo-potential) for Br

[[File:Bbr3 opt by416.png]]

Item Value Threshold Converged?
Maximum Force 0.000023 0.000450 YES
RMS Force 0.000014 0.000300 YES
Maximum Displacement 0.000118 0.001800 YES
RMS Displacement 0.000069 0.001200 YES

{{DOI|10042/202469}}

[[File:By416 bbr3 freq3.log]]

Low frequencies --- -3.1706 -0.0002 -0.0001 0.0000 1.6540 3.3467
Low frequencies --- 155.8924 155.9627 267.7046

<jmol><jmolApplet>
<title>BBr3 molecule</title>
<color>black</color>
<size>300</size>
<uploadedFileContents>By416 bbr3 freq3.log</uploadedFileContents>
</jmolApplet></jmol>

'''Project'''

'''Aromaticity'''

'''Benzene'''

Method:B3LYP

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

[[File:Benzene opt2 by416.PNG]]

Item Value Threshold Converged?
Maximum Force 0.000198 0.000450 YES
RMS Force 0.000082 0.000300 YES
Maximum Displacement 0.000849 0.001800 YES
RMS Displacement 0.000305 0.001200 YES

[[File:BENZENE FREQ BY416.LOG]]

Low frequencies --- -11.6728 -0.0010 -0.0008 0.0003 6.6686 15.6846
Low frequencies --- 414.0392 414.6031 621.0860

<jmol><jmolApplet>
<title>Benzene</title>
<color>black</color>
<size>400</size>
<uploadedFileContents>BENZENE FREQ BY416.LOG</uploadedFileContents>
</jmolApplet></jmol>

'''Charge distribution:'''

[[File:Benzene chargedist by416 2.PNG]]

Charges:
Carbon = -0.239
Hydrogen = 0.239

Discussion:

In benzene, every carbon atom has the same electronegativity, therefore has the same charge. The same applies to the hydrogen atoms. The hydrogen atoms have the same magnitude of charge as carbon, but the opposite sign.

'''Borazine'''

Method:B3LYP

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

[[File:Borazine opt2 by416.PNG]

Item Value Threshold Converged?
Maximum Force 0.000073 0.000450 YES
RMS Force 0.000026 0.000300 YES
Maximum Displacement 0.000298 0.001800 YES
RMS Displacement 0.000106 0.001200 YES

[[File:BORAZINE FREQ2 BY416.LOG]]

Low frequencies --- -15.3480 -15.3480 -12.7393 -0.0158 -0.0107 -0.0107
Low frequencies --- 288.9049 288.9049 403.7235

<jmol><jmolApplet>
<title>Borazine</title>
<color>black</color>
<size>400</size>
<uploadedFileContents>BORAZINE FREQ BY416.LOG</uploadedFileContents>
</jmolApplet></jmol>

'''Charge distribution:'''

[[File:Borazine chargedist by416.PNG]]

Charges:

Nitrogen= -1.102
Hydrogen atoms bonded to Nitrogen= 0.432
Boron= 0.747
Hydrogen atoms bonded to Boron= -0.077

Discussion:

Nitrogen is much more electronegative than boron and hydrogen. Therefore, it pulls electron density from orbitals of B and H, towards itself. As a result the hydrogen atoms bonded to nitrogen have a positive charge because electron density has been pulled away. On the other hand, boron is less electronegative than nitrogen so does not pull as much electron density towards itself. Therefore, it has a less negative charge and its electron density is dispersed on the hydrogen. Hence the hydrogen atoms bonded to boron are more negative than the hydrogen atoms bonded to nitrogen.

'''Charge Comparison'''

Borazine has N - H bonds which are more polar than benzene and B - H bonds which are less polar than benzene. This is because nitrogen is more electronegative than carbon. Hence creating bonds with a greater charge difference/ more polar. Boron is less electronegative than carbon therefore there is lower charge difference between B-H than C-H

'''MO Comparisons'''

1.

[[File:Benzene mo 2 by416.PNG]]

[[File:Borazine MO 2 by416.PNG]]

2.

[[File:Benzene mo 3 by416.PNG]]

[[File:Borazine mo 3 by416.PNG]]

3.

[[File:Benzene mo 4 by416.PNG]]

[[File:Borazine mo 4 by416.PNG]]

'''Aromaticity'''

File:NH3BH3 by416 opt.png

2018-05-24T13:50:44Z

By416: