Rep:Mod:danbanh

BH3

B3LYP/6-21G level

Item table

Item                      Value        Threshold    Converged?
 Maximum Force            0.000158     0.000450     YES
 RMS     Force            0.000079     0.000300     YES
 Maximum Displacement     0.000622     0.001800     YES
 RMS     Displacement     0.000311     0.001200     YES

Low frequencies

 Low frequencies ---   -0.2456   -0.1129   -0.0054   44.0270   45.1846   45.1853
 Low frequencies --- 1163.6049 1213.5924 1213.5951

Link to log file: here

BH3 Jmol image

BH3

Link to log file: here

Vibrations

Table of vibrational modes in BH3
Stretching frequency (1/cm)	Stretching intensity (%)	Type of vibration	IR Active?
1164	92	Bend out of plane	Yes
1214	14	Bend in plane	Yes
1214	14	Bend	Yes
2580	0	Symmetric stretch	No
2713	126	Asymmetric stretch	Yes
2713	126	Asymmetric stretch	Yes

]

Whilst there are 6 vibrations for BH3, there are fewer than 6 IR peaks present in the IR spectrum. There are 3 peaks present, 2 of which correspond to 2 degenerate vibrational modes. There are degenerate modes at: 1214/cm and 2713/cm. The final peak present corresponds to an out of plane bend at 1164/cm.

Ng611 (talk) 14:09, 27 May 2019 (BST) What about the non-IR active stretch at 2580 wavenumbers?

BH3 MO diagram

]

Ng611 (talk) 14:14, 27 May 2019 (BST) One of your e' orbitals (the right hand one) doesn't seem correct. Pay close attention to the phase relationship.

The LCAO MO description is a reasonably accurate general picture of the distribution of electron density. However, it isn't a perfect description or the real MOs. The real MOs are more diffuse and spread out compared to the LCAO model which constrains electron density to orbitals on atoms rather than across the whole molecule. This shows that qualitative MO analysis is accurate, and useful, but not perfect due to the lack of precision about the distribution of electron density across the whole molecule.

Ng611 (talk) 14:14, 27 May 2019 (BST) There's a more significant discrepancy between the qualitative and quantitative MO theory that you've missed. What do you think it could be?

-Diagram adapted from: Professor T.Hunt, Imperial College London, Lecture_4_Tut_MO_diagram_BH3

Association Energy

NH3

  
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
 Predicted change in Energy=-9.843852D-11

Low frequencies ---   -0.0138   -0.0032   -0.0015    7.0783    8.0932    8.0937
 Low frequencies --- 1089.3840 1693.9368 1693.9368

Link to log file: here

NH3

Link to log file: here

NH3BH3

  
Item                      Value        Threshold    Converged?
 Maximum Force            0.000121     0.000450     YES
 RMS     Force            0.000057     0.000300     YES
 Maximum Displacement     0.000507     0.001800     YES
 RMS     Displacement     0.000295     0.001200     YES
 Predicted change in Energy=-1.613116D-07

Low frequencies ---   -0.0252   -0.0030    0.0008   17.0357   17.0380   36.8914
 Low frequencies ---  265.7448  632.2122  639.3345

Link to log file: here

NH3BH3

Link to log file: here

Association energy calculation

E(NH3)= -56.55776873, E(BH3)= -26.61532349, E(NH3BH3)= -83.22468892, ΔE= E(NH3BH3)- [E(NH3)+ E(BH3)], ΔE= -0.0515967 au ΔE= -135 KJ/mol

The calculated energy of the B-N bond is low. This means that the dative B-N bond can be considered as weak. C-C has a bond strength of 346 KJ/mol whilst the weak F-F bond has a bond strength of 155 KJ/mol [1].

Ng611 (talk) 14:16, 27 May 2019 (BST) Good calculation and good bond comparison! Try to use a source from a textbook or databook, rather than the web.

NI3

Item                      Value        Threshold    Converged?
 Maximum Force            0.000000     0.000015     YES
 RMS     Force            0.000000     0.000010     YES
 Maximum Displacement     0.000001     0.000060     YES
 RMS     Displacement     0.000000     0.000040     YES
 Predicted change in Energy=-1.540748D-14

Low frequencies ---  -12.5584  -12.5522   -6.0136   -0.0040    0.0191    0.0663
 Low frequencies ---  100.9979  100.9986  147.3400

Link to log file: here

N-I bond length: 2.030 Å

Ng611 (talk) 14:18, 27 May 2019 (BST) Slighly off the correct value here. Did you repeat your optimisation?

NI3

Link to log file: here

Ionic Liquids

[N(CH3)4]+

Item                      Value        Threshold    Converged?
 Maximum Force            0.000073     0.000450     YES
 RMS     Force            0.000018     0.000300     YES
 Maximum Displacement     0.000277     0.001800     YES
 RMS     Displacement     0.000088     0.001200     YES
 Predicted change in Energy=-5.328712D-08

Low frequencies ---    0.0007    0.0010    0.0013   35.6290   35.6290   35.6290
 Low frequencies ---  215.5240  315.1230  315.1230

Link to log file: here

[N(CH3)4]+

[P(CH3)4]+

Item                      Value        Threshold    Converged?
 Maximum Force            0.000138     0.000450     YES
 RMS     Force            0.000035     0.000300     YES
 Maximum Displacement     0.000718     0.001800     YES
 RMS     Displacement     0.000298     0.001200     YES
 Predicted change in Energy=-1.829332D-07

Low frequencies ---   -0.0042   -0.0041   -0.0017   51.6355   51.6355   51.6355
 Low frequencies ---  188.7480  213.6021  213.6021

Link to log file: here

[P(CH3)4]+

Charge Distribution Analysis

Charge Distribution of [N(CH3)4]+
Atom	Charge (C)
Nitrogen	-0.296
Carbon	-0.483
Hydrogen	0.269

Charge Distribution [P(CH3)4]+
Atom	Charge (C)
Phosphorus	1.666
Carbon	-1.060
Hydrogen	0.298

]

In the valence model of [N(CH3)4]+, the positive charge would be localised on the Nitrogen atom. However, as Nitrogen is highly electronegative, the inductive effect pulls electron density from the methyl groups towards the Nitrogen centre, thus, resulting in a more negative charge distribution around the centre of the molecule. Positive charge is therefore localised on the Hydrogen atoms. The Phosphorus, however, has a local positive charge. This is due to Phosphorus being more electropositive compared to the Carbon atoms resulting in electron density being pulled away from the Phosphorus centre.

Ng611 (talk) 14:21, 27 May 2019 (BST) Good discussion of electronegativity. What about the effect of symmetry? You should also discuss the charge on the carbon atoms in NMe4+ and the breakdown of the formal charge picture.

MO Visualisation

Table of MOs in [N(CH3)4]+
MO	LCAO	Real MO
MO8
MO10
MO21

Ng611 (talk) 14:28, 27 May 2019 (BST) Your FOs for MO10 should be s-type, not p-type. Otherwise, outstanding LCAO analysis.

References

[1]: Strength of Covalent bonds, Chemistry Libretexts: https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_Chemistry_-_The_Central_Science_(Brown_et_al.)/08._Basic_Concepts_of_Chemical_Bonding/8.8%3A_Strength_of_Covalent_Bonds (Accessed 19/05/19)