Rep:Mod:SW1816

EX₃ Section

BH₃

Optimisation of BH₃

Method: B3LYP

Basis set: 6-21G

A Gaussview image of an optimised borane molecule.

 Item                       Value     Threshold  Converged?
 Maximum Force            0.000006     0.000450     YES
 RMS     Force            0.000003     0.000300     YES
 Maximum Displacement     0.000023     0.001800     YES
 RMS     Displacement     0.000011     0.001200     YES
 Predicted change in Energy=-1.996524D-10

Vibrational spectrum for BH₃

File:Shangwang bh3 freq.txt

 Low frequencies ---   -0.9432   -0.8611   -0.0054    5.7455   11.7246   11.7625
 Low frequencies --- 1162.9963   1213.1826   1213.1853

Mode	Wavenumber(cm-1)	Intensity	Assignment	IR active
1	1163.00	92.5482	out-of-plate bending	Yes
2	1213.18	14.0551	bending	Slight
3	1213.19	14.0587	bending	Slight
4	2582.28	0.0000	Symmetric stretching	No
5	2715.45	126.3302	Asymmetric stretching	Yes
6	2715.45	126.3206	Asymmetric stretching	Yes

IR Spectrum of a Borane Molecule.

There are only 3 peaks in the IR spectrum of the borane molecule, but the BH₃ molecule has 6 vibrations. In the modes of vibrations, the Mode 2 and Mode 3 of bending are degenerate and the Mode 5 and Mode 6 of asymmetric stretching are degenerate. The Mode 3 is not IR active because symmetric stretching (Mode 3) has no changing dipole moment.

Borane molecule

Association Energy of BBr₃

E(NH₃) = -56.55777 a.u. = -148492 kJmol^-1

E(BH₃) = -26.61532 a.u. = -69879 kJmol^-1

E(NH₃BH₃) = -83.22469 a.u. = -218506 kJmol^-1

ΔE=E(NH₃BH₃)-[E(NH₃)+E(BH₃)] = -218506 -(-69879 -148492)= -135 kJmol^-1

Ng611 (talk) 20:48, 17 May 2018 (BST) Remember to cite your bond values (ideally from a textbook, databook, or paper).

MO diagram of BH₃

The MO diagram of a Borane Molecule.

Ng611 (talk) 20:49, 17 May 2018 (BST)From comparing the calculated and qualitative MOs, are there any differences at all between them, and what does this tell you about qualitative MO theory?

The orbital with lowest energy is contributed by the 1s orbital shown in the right-bottom orbital figure. The other orbitals matches the theoretical MO diagram.

BBr₃

BBr₃ Boron tribromide

Optimisation of BBr₃

Method: B3LYP

Basis set: GEN

A Gaussview image of an optimised boron tribromide molecule.

  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
 Predicted change in Energy=-4.027380D-10

Vibrational spectrum for BBr₃

File:Shangwang bbr3 freq.txt

   Low frequencies ---   -0.0137   -0.0064   -0.0046    2.4315    2.4315    4.8421
   Low frequencies ---  155.9631  155.9651  267.7052

 Mode    Freq    Intensity  IR active   Asssignment
  1      155.96    0.0843    Slightly     bending
  2      155.97    0.0843    Slightly     bending
  3      267.71    0.0000       No    Symmetric stretch
  4      377.64    3.6524    Slightly     
  5      762.85    319.5226     Yes   Asymmetric stretch
  6      762.89    319.5479     Yes   Asymmetric stretch

IR Spectrum of a Boron Tribromide Molecule.

Boron tribromide molecule

Project Aromaticity Section

benzene

Method: B3LYP

Basis set: 6-21G

A Gaussview image of an optimised benzene molecule.

         Item               Value     Threshold  Converged?
 Maximum Force            0.000203     0.000450     YES
 RMS     Force            0.000078     0.000300     YES
 Maximum Displacement     0.000824     0.001800     YES
 RMS     Displacement     0.000287     0.001200     YES
 Predicted change in Energy=-4.357942D-07
 

File:Shangwang benzene freq.txt

 Low frequencies ---   -2.5530   -2.5530   -0.0088   -0.0041   -0.0041   10.3930
 Low frequencies ---  413.9723  413.9723  621.1358 

IR Spectrum of a Benzene Molecule.

Benzene molecule

Borazine

Method: B3LYP

Basis set: 6-21G

A Gaussview image of an optimised borazine molecule.

         Item               Value     Threshold  Converged?
 Maximum Force            0.000167     0.000450     YES
 RMS     Force            0.000077     0.000300     YES
 Maximum Displacement     0.000738     0.001800     YES
 RMS     Displacement     0.000283     0.001200     YES
 Predicted change in Energy=-8.253056D-07

 

File:Shangwang borazine freq.txt

 Low frequencies ---   -0.0137   -0.0064   -0.0046    2.4315    2.4315    4.8421
 Low frequencies ---  155.9631  155.9651  267.7052

IR Spectrum of a Borazine Molecule.

Borzaine molecule

Charge distribution

The charge distribution comparison of bezene and borazine

MO diagrams of benzene and borazine

Obitial 1.

Obitial 2.

Obitial 3.

Obitial 4.

Obitial 5.

Aromaticity

The aromatic ring can not be considered as basic overlay of pz orbitals, as the electrons in aromatic rings are delocalised. Also due to the hybridisation, the orbital mixing is not condered as vertical as pz.

This report was missing several sectiona. I saw no calculations for BH3NH3 or NH3. and large parts of your mini project were largely absent. Your MO analysis seemed to look at core orbitals as opposed to valence orbitals? Your section on aromaticity also needed far more detail than just a line or two. Your charge analysis for benzene/borazine was good however.