Rep:Mod:by1517inorganic

EX₃Section

BH₃

Computational level and basis set :B3LYP / 6-31G(d,p)

Optimization

 

          Item               Value     Threshold  Converged?

 Maximum Force            0.000011     0.000450     YES

 RMS     Force            0.000007     0.000300     YES

 Maximum Displacement     0.000043     0.001800     YES

 RMS     Displacement     0.000028     0.001200     YES

 Predicted change in Energy=-6.856714D-10

 Optimization completed.

    -- Stationary point found.

Frequency analysis log file

Low frequencies

 Low frequencies ---   -7.5936   -1.5614   -0.0054    0.6514    6.9319    7.1055
 Low frequencies --- 1162.9677 1213.1634 1213.1661

Optimized BH3

IR

Wavenumber (cm^-1)	IR intensity	Symmetry	IR active	Vibration type
1163	93	A₂''	Y	Out-of-plane wagging
1213	14	E'	Y, not visible	In-plane scissoring
1213	14	E'	Y, not visible	In-plane rocking
2582	0	A₁'	N	Symmetrical stretching
2716	126	E'	Y	Asymmetrical stretching
2716	126	E'	Y	Asymmetrical stretching

Out of the 6 vibrational modes, there is only 1 inactive mode at 2582 cm^-1as there is no change in dipole moment for this mode. However, the spectrum only show 3 visible peaks. This is due to the 2 degenerate vibration pairs, which are at 1213 cm^-1and 2716 cm^-1, these show up as a single peak, adding in a peak at 1163 cm^-1, a total of 3 peaks can be seen.

Molecular Orbitals of BH₃

NH₃

Computational level and basis set :B3LYP / 6-31G(d,p)

Optimization

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=-9.843521D-11

 Optimization completed.

    -- Stationary point found.

Optimization + Frequency analysis log file

Low frequencies

Low frequencies ---   -0.0129   -0.0024   -0.0016    7.1031    8.1045    8.1048

Low frequencies --- 1089.3834 1693.9368 1693.9368

Optimized NH3

NH₃BH₃

Computational level and basis set :B3LYP / 6-31G(d,p)

Optimization

Item               Value     Threshold  Converged?

 Maximum Force            0.000121     0.000450     YES

 RMS     Force            0.000057     0.000300     YES

 Maximum Displacement     0.000564     0.001800     YES

 RMS     Displacement     0.000316     0.001200     YES

 Predicted change in Energy=-1.705954D-07

 Optimization completed.

    -- Stationary point found.

Frequency analysis log file

Low Frequencies

 Low frequencies ---   -0.0253   -0.0034   -0.0012   17.0275   17.0301   36.9251

 Low frequencies ---  265.7528  632.2151  639.3365

Optimized NH3BH3

E(NH₃) = - 56.56 a.u.

E(BH₃) = - 26.63 a.u.

E(NH₃BH₃) = - 83.22 a.u.

ΔE = E(NH₃BH₃)-[E(NH₃)+E(BH₃)] = -0.052 a.u. = -136.526 kJ mol^-1

Compared to the C-C bond which has a bond strength of 347 kJ mol^-1^[1], the B-N bond is very weak.

NI₃

Computational level and basis set :B3LYP / 6-31G(d,p)

Optimization

         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

 Predicted change in Energy=-5.826109D-08

 Optimization completed.

    -- Stationary point found.

Optimization + Frequency analysis log file

Low frequencies

 Low frequencies ---  -12.7380  -12.7319   -6.2907   -0.0039    0.0188    0.0633

 Low frequencies ---  101.0326  101.0333  147.4124

Optimized NI3

The optimized N - I distance is 2.18362 Å

Project section - Ionic Liquids

[N(CH₃)₄]⁺

Computational level and basis set :B3LYP / 6-31G(d,p) LANL2DZ

C - N bond length : 1.509 Å

C - H bond length : 1.090 Å

Optimization

         Item               Value     Threshold  Converged?

 Maximum Force            0.000068     0.000450     YES

 RMS     Force            0.000027     0.000300     YES

 Maximum Displacement     0.000155     0.001800     YES

 RMS     Displacement     0.000067     0.001200     YES

 Predicted change in Energy=-9.049902D-08

 Optimization completed.

    -- Stationary point found.

Optimization + Frequency analysis log file

Low Frequency

Low frequencies ---    0.0001    0.0008    0.0008   22.7173   22.7173   22.7173

 Low frequencies ---  190.7547  294.0687  294.0687

Optimized BH3

[P(CH₃)₄]⁺

Computational level and basis set :B3LYP / 6-31G(d,p)

C - P bond length : 1.817 Å

C - H bond length : 1.093 Å

Optimization

 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

 Predicted change in Energy=-1.587537D-07

 Optimization completed.

    -- Stationary point found.

Optimization + Frequency analysis log file

Low Frequency

Low frequencies ---    0.0018    0.0022    0.0029   26.3168   26.3168   26.3169

 Low frequencies ---  160.9764  195.4756  195.4756

Optimized P(CH3)4+

[N(CH₃)₄]⁺vs[P(CH₃)₄]⁺charge distributions

	Charge on Carbon	Charge on Hydrogen	Charge on Central atom
Charge distribution on [N(CH₃)₄]⁺	-0.48	0.27	-0.30
Charge distribution on [P(CH₃)₄]⁺	-1.06	0.30	1.67

In both molecules, carbon carries negative charges and hydrogen carries positive charges. In [N(CH₃)₄]⁺, nitrogen is the most electronegative atom within this ion so a negative charge is expected. The charge analysis does show nitrogen carrying a negative charge. However, the carbon atoms actually carry most of the negative charge and individual carbon atoms are more negative than the nitrogen atom. This is perhaps due to the need for nitrogen to donate its lone pair for a dative covalent bond with a methyl carbocation. This leaves nitrogen with less negative charge. In addition with 3 electropositive hydrogens attached to each of the carbon, carbons would be the most negatively charged atom in the ion. This leaves each of the hydrogens with about a quarter of a positive charge

For [P(CH₃)₄]⁺, phosphorus is the most electropositive atom in the ion, so the carbon atoms would pull electron density from phosphorus in addition to the donation of the phosphorus' lone pair to a methyl group, leaves the phosphorus atom very positively charged at 1.67. Conversely, carbon being the most electronegative, carries the negative charge in the molecule, each holding -1.06 due to the pulling of electron density from phosphorus and hydrogen. The hydrogens, like in [N(CH₃)₄]⁺, are all similarly positively charged, with only slightly more positive charge. In comparison with the central atom as N, P is actively pushing electrondensity away so that the carbon atoms are only pulling electron density towards it whereas with N carbon is pulling electron density from H and pushing electron density to N.

In the traditional depiction, the formal positive is assigned to the nitrogen. This charge is assigned assuming that all of the electrons in bonds are shared equally among all atoms, disregarding the difference in electronegativity between atoms. Since nitrogen have donated an entire lone pair to form a σ bond, the positive charge is assigned to it. However, charge analysis shows that this is not the case and in fact the positive charge is distributed among the H atoms. Because of this distribution of charge, there are neutral regions within the ions between the positively charged and negatively charged atoms. In [N(CH₃)₄]⁺, there are neutral regions between C and H atoms while in [P(CH₃)₄]⁺ there is an additional region between P and C atoms.

[N(CH₃)₄]⁺Molecular Orbitals

MO number

Energies (Hartree)

MO visualization

LCAO Drawing

3D model of MO

MO7

-0.93

MO7

MO15

-0.62

MO15

MO16

-0.58

MO16

↑ https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Chemical_Bonding/Fundamentals_of_Chemical_Bonding/Bond_Energies

[1] ttps://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Chemical_Bonding/Fundamentals_of_Chemical_Bonding/Bond_Energies

[1]

EX3 Section

BH3

Computational level and basis set :B3LYP / 6-31G(d,p)

Optimization

Low frequencies

IR

Molecular Orbitals of BH3

NH3

Computational level and basis set :B3LYP / 6-31G(d,p)

Optimization

Low frequencies

NH3BH3

Computational level and basis set :B3LYP / 6-31G(d,p)

Optimization

Low Frequencies

NI3

Computational level and basis set :B3LYP / 6-31G(d,p)

Optimization

Low frequencies

Project section - Ionic Liquids

[N(CH3)4]+

Computational level and basis set :B3LYP / 6-31G(d,p) LANL2DZ

Optimization

Low Frequency

[P(CH3)4]+

Computational level and basis set :B3LYP / 6-31G(d,p)

Optimization

Low Frequency

[N(CH3)4]+ vs [P(CH3)4]+ charge distributions

[N(CH3)4]+ Molecular Orbitals

EX₃Section

BH₃

Molecular Orbitals of BH₃

NH₃

NH₃BH₃

NI₃

[N(CH₃)₄]⁺

[P(CH₃)₄]⁺

[N(CH₃)₄]⁺vs[P(CH₃)₄]⁺charge distributions

[N(CH₃)₄]⁺Molecular Orbitals