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Borane,BH3

Method/Basis set: B3LYP/6-31G


         Item               Value     Threshold  Converged?
 Maximum Force            0.000046     0.000450     YES
 RMS     Force            0.000023     0.000300     YES
 Maximum Displacement     0.000182     0.001800     YES
 RMS     Displacement     0.000091     0.001200     YES

Frequency analysis log file: HAJAR_BH3_FREQ.LOG

Low frequencies ---   -0.4072   -0.1962   -0.0054   25.2514   27.2430   27.2460
Low frequencies --- 1163.1897 1213.3128 1213.3155
BH3

Vibrational spectrum for BH3

wavenumber (cm-1 Intensity (arbitrary units) symmetry IR active? type
1163 92 A2 yes out-of-plane bend
1213 14 E very slight bend
1213 14 E very slight bend
2581 0 A1 no symmetric stretch
2714 126 E yes asymmetric stretch
2714 126 E yes asymmetric stretch

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Although there are 6 vibrations, there are only 3 observed peaks on the IR spectrum. Some of the vibrations have the same wavenumbers as well as intensities indicating that they are degenerate. This gives rise to a single peak. There are two sets of degenerate vibrations. The symmetric stretch does not give rise to a peak because it is IR inactive.

LCAO MOs vs Real MOs


Ng611 (talk) 01:58, 15 May 2019 (BST) Your assignments are correct, although you could have just used the full MO diagram from Trish's lecture and saved yourself the trouble of cropping the orbitals out.

The MOs derived from LCAO are placed next to their respective 'real' MOs. The'LCAO' MOs are taken from Professor Patricia Hunt's lecture course notes http://www.huntresearchgroup.org.uk/teaching/teaching_comp_lab_year2a/Tut_MO_diagram_BH3.pdf


There are no significant differences between the two MOs. The MOs derived from LCAO predicts the 'real' MOs quite well. The extent of diffusion of predicted orbitals vary a little from the real orbitals but generally, the shapes and phases of orbitals are very well predicted. These predictions from MO theory is a useful method in understanding how particles behave.

Ng611 (talk) 01:59, 15 May 2019 (BST) You mention that the deviate slightly. Could you be more specific?

Ammonia,NH3

Method/Basis set: B3LYP/6-31G


         Item               Value     Threshold  Converged?
 Maximum Force            0.000006     0.000450     YES
 RMS     Force            0.000004     0.000300     YES
 Maximum Displacement     0.000014     0.001800     YES
 RMS     Displacement     0.000009     0.001200     YES

Frequency analysis log file: HNA_NH3_FREQ.LOG

Low frequencies ---   -8.5646   -8.5588   -0.0041    0.0455    0.1784   26.4183
Low frequencies --- 1089.7603 1694.1865 1694.1865
 
BH3

NH3BH3

Method/Basis set: B3LYP/6-31G


   Item               Value     Threshold  Converged?
 Maximum Force            0.000123     0.000450     YES
 RMS     Force            0.000058     0.000300     YES
 Maximum Displacement     0.000515     0.001800     YES
 RMS     Displacement     0.000296     0.001200     YES

Frequency analysis log file: HNA_NH3BH3_FREQ.LOG

Low frequencies ---  -12.7929    0.0011    0.0013    0.0014   19.1979   42.4752
Low frequencies ---  266.1842  632.1568  638.1636

BH3

Association energy


E(NH3)   = -26.6153 a.u
E(BH3)   = -56.5578 a.u
E(NH3BH3)= -83.2247 a.u

ΔE=E(NH3BH3)-[E(NH3)+E(BH3)] = -83.2247 - (-56.5578-26.6153) = -0.0516 a.u * 2625.5 kJ/mol = -135.48 kJ/mol
B-N dative bond is quite weak compared to N-N bond which has energy of about 160 kJ/mol or compared to B-B bond of about 293 kJ/mol.

Ng611 (talk) 02:01, 15 May 2019 (BST) Good calculation. You should remember that your calculations are only accurate to about ~1 kJ/mol (and should be reported appropriately). Remember also to cite the sources you obtained your bond energies from!

NI3

Method/Basis set: B3LYP/6-31G


   
         Item               Value     Threshold  Converged?
 Maximum Force            0.000061     0.000450     YES
 RMS     Force            0.000037     0.000300     YES
 Maximum Displacement     0.000459     0.001800     YES
 RMS     Displacement     0.000285     0.001200     YES

My frequency analysis keeps running into error no matter how many people come to help me.

NI3

Al2Br2Cl4


Isomer(a)
Isomer(b)

Difference in energy between isomer(a) and isomer(b) = 0.005 a.u = -13.13 kJ/mol

From data obtained,isomer (b) with Cl as bridging atoms is more stable than isomer (a) with Br as bridging atoms. Cl is smaller than Br which gives it a better overlap with adjacent Al atom. Al-Cl bond is stronger than Al-Br bond.

Note from editor

I didn't mean to not finish this. I have tried my very best to finish this before 6pm of Friday but I didn't manage to. Persoanlly I find this task difficult and I ran into a lot of error which took a lot of time hence I couldn't finish it, I'm terribly sorry :(

Ng611 (talk) 02:12, 15 May 2019 (BST) I'm really sorry you found it difficult. However, you did excellently in your first section (and managed to pass the lab as a result, which is impressive!). The fact that you were able to do the calculations correctly in section 1 suggests to me that it's well within your abilities to do the work, even if you did struggle.

I'd suggest at some point (when you have some free time), that you go over the second section at a more leisurely pace (and without the pressure of submitting a report) and see how you get on. Otherwise, well done on a good first section!