Rep:Mod:yht17

Part 1

BH₃

Method: RB3LYP

Basis set: 6-31G(d,p)

         Item               Value     Threshold  Converged?
 Maximum Force            0.000006     0.000450     YES
 RMS     Force            0.000004     0.000300     YES
 Maximum Displacement     0.000023     0.001800     YES
 RMS     Displacement     0.000015     0.001200     YES

Frequency analysis log file: YHT17_BH3_FREQ.LOG

 Low frequencies ---   -2.2126   -1.0751   -0.0055    2.2359   10.2633   10.3194
 Low frequencies --- 1162.9860 1213.1757 1213.1784

Optimised BH3 molecule

Vibrations of BH₃

Vibration	Frequency (cm-1)	Intensity (au)	Symmetry	IR active?	Type
1	1163	93	a2"	Yes	Out-of-plane bend
2	1213	14	e'	Very slight	In-plane bend
3	1213	14	e'	Very slight	In-plane bend
4	2582	0	a1'	No	Symmetric stretch
5	2715	126	e'	Yes	Asymmetric stretch
6	2715	126	e'	Yes	Asymmetric stretch

There are 6 vibration modes, but only three peaks can be seen on the spectrum. For a vibration mode to be IR active, it must involve a change in dipole moment. As mode 4 is totally symmetric, it does not involve a change in dipole moment and therefore does not appear on the IR spectrum. Out of the 5 vibration modes that do involve a change in dipole moment, there are two degenerate pairs. Modes 2 and 3 have the same frequency, as do modes 5 and 6. These degenerate pairs overlap on the spectrum and appear as 1 peak each. As a result, there are only 3 visible peaks on the spectrum.

Good explanation with both reasons given, the detail of the bend types in the vibrational analysis table is also good. Smf115 (talk) 21:27, 1 June 2019 (BST)

MO Diagram:

MO theory predicts the combinations of the atomic orbitals well, as well as any degenerate MOs. It can predict the approximate shapes of the MOs, but there is quite a large deviation from the actual shapes, so it cannot predict the effects of the orbital shapes on reactivity very well.

Clear inclusion of the calculated MOs with the LCAO MOs on to the diagram. Your comparison of the two is ok but very brief and general, it would have been good to see you consider some of the specific differences by looking at the 2e' or 3a1' orbitals for example. Smf115 (talk) 21:30, 1 June 2019 (BST)

NH₃

Method: RB3LYP

Basis set: 6-31G(d,p)

         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

Frequency analysis log file: YHT17_NH3_FREQ.LOG

 Low frequencies ---   -8.4776   -8.4300   -0.0027    0.0337    0.1929   26.4250
 Low frequencies --- 1089.7611 1694.1863 1694.1866

Optimised NH3 molecule

NH₃BH₃

Method: RB3LYP

Basis set: 6-31G(d,p)

         Item               Value     Threshold  Converged?
 Maximum Force            0.000233     0.000450     YES
 RMS     Force            0.000083     0.000300     YES
 Maximum Displacement     0.001201     0.001800     YES
 RMS     Displacement     0.000369     0.001200     YES

Frequency analysis log file: YHT17_NH3BH3_FREQ.LOG

 Low frequencies ---   -0.0757   -0.0463   -0.0111   18.3546   18.5273   44.8329
 Low frequencies ---  266.2035  634.6082  640.2843

Optimised NH3BH3 molecule

NH₃-BH₃ Association Energy

E(BH₃) = -26.6153 au

E(NH₃) = -56.5577 au

E(NH₃BH₃) = -83.2246 au

ΔE = -0.0516 au = -135 kJ mol^-1

Compared to most other single bonds, this is quite a weak bond.

Your calculated value is correct but you haven't shown the calculation at all. The bond strength should have also been evaluated by comparing against some relevant literature bond dissociation energies. Smf115 (talk) 21:34, 1 June 2019 (BST)

NI₃

Method: RB3LYP

Basis set: N: 6-31G(d,p), I: LanL2DZ

         Item               Value     Threshold  Converged?
 Maximum Force            0.000068     0.000450     YES
 RMS     Force            0.000044     0.000300     YES
 Maximum Displacement     0.000493     0.001800     YES
 RMS     Displacement     0.000333     0.001200     YES

Frequency analysis log file: Yht17_ni3_freq.log

Due to an error, the log file could not be published to D-space, so instead it has been uploaded to this wiki.

 Low frequencies ---  -12.7380  -12.7319   -6.2907   -0.0040    0.0188    0.0633
 Low frequencies ---  101.0326  101.0333  147.4124

Optimised NI3 molecule

The optimised N-I bond length is 2.184 Å.

Part 2 - Project: Ionic Liquids

[N(CH₃)₄]⁺

Method: RB3LYP

Basis set: 6-31G(d,p)

         Item               Value     Threshold  Converged?
 Maximum Force            0.000067     0.000450     YES
 RMS     Force            0.000017     0.000300     YES
 Maximum Displacement     0.000252     0.001800     YES
 RMS     Displacement     0.000081     0.001200     YES

Frequency analysis log file: YHT17_NME4_FREQ.LOG

 Low frequencies ---    0.0009    0.0013    0.0013   35.2977   35.2977   35.2977
 Low frequencies ---  217.4079  316.4871  316.4871

Optimised [N(CH3)4]+ ion

[P(CH₃)₄]⁺

Method: RB3LYP

Basis set: 6-31G(d,p)

         Item               Value     Threshold  Converged?
 Maximum Force            0.000128     0.000450     YES
 RMS     Force            0.000032     0.000300     YES
 Maximum Displacement     0.000666     0.001800     YES
 RMS     Displacement     0.000277     0.001200     YES

Frequency analysis log file: YHT17_PME4_FREQ.LOG

 Low frequencies ---   -0.0031   -0.0028   -0.0001   51.2698   51.2698   51.2698
 Low frequencies ---  186.5950  211.3904  211.3904

Optimised [P(CH3)4]+ ion

Charge Distributions

Distribution of charge on ions

Ion	Image	Charge on central atom (N/P)	Charge per C atom	Charge per H atom
[N(CH3)4]+		N: -0.30	C: -0.48	H: +0.27
[P(CH3)4]+		P: +1.67	C: -1.06	H: +0.30

The charge spread is quite different between the two ions. In the nitrogen ion, N is the most electronegative element, so the N atom has a negative charge. However, the C atoms have more negative charge because they are each surrounded by 3 H atoms, which is the most electropositive element. The positive charge is all spread out over the H atoms. This is in contrast to the location of the charge in a traditional depiction, where the positive charge would be on the N atom. This is because the traditional depiction does not take into account the electronegativities of atoms, it assumes electron density is evenly distributed in a bond.

In the phosphorus ion, P is more electropositive than C and about the same as H. Thus, the P atom does have a positive charge, and in fact has more positive charge than in a traditional depiction.

In both ions, the H atoms have a similar charge, suggesting that the inductive effect from the central atom has minimal effect.

Correct NBO charges calculated and good use of a uniform charge distribution across both ILs. Your discussion using the relative electronegativities is ok but could be improved by including electronegativity values, for example, and could be a bit more developed. Smf115 (talk) 18:57, 4 June 2019 (BST)

Nice mention that the traditional picture doesn't account for electronegativity, however, you haven't explained why the +1 formal charge on the N arises (consider formal electron counting/Lewis structures). Smf115 (talk) 18:57, 4 June 2019 (BST)

[N(CH₃)₄]⁺ Molecular Orbitals

MO number	Energy (au)	JSmol image	Still image	LCAO diagram	Bonding character
21 (HOMO)	-0.5793				Weakly bonding
16	-0.5804				Non-bonding
12	-0.6989				Strongly bonding

Very nicely presented with good use of jmols. You've chosen a good range of MOs which is great to see and your final evaluations of the MO character are good. The FOs for MO12 and 16 are not correct though and it would have helped to apply the BH₃ MO diagram to CH₃ to identify the correct ones. To improve, it would have also been nice to see some analysis to justify the evaluated MO character. Smf115 (talk) 19:07, 4 June 2019 (BST)

Overall, a good report which lacked further analysis in the project section. Smf115 (talk) 19:07, 4 June 2019 (BST)