Lab:Mccalllo

Marking

You did a good job. It was nice to see you inlcude a picture of the acetate HOMO alongside the description of the primarily contributing atoms. It would be good if you could pay more attention to rounding values to the correct dp.
If you have any specific questions, do e-mail Prof. Hunt

NH₃ Molecule

Calculation Data

name of submitted log file	NH3_OPT_LM.log
calculation method	RB3LYP
basis set	6-31G(d,p)
final energy	-56.557769
RMS gradient	0.000000
point group	C3V

Item Table

Item               Value     Threshold  Converged?
 Maximum Force            0.000000     0.000015     YES
 RMS     Force            0.000000     0.000010     YES
 Maximum Displacement     0.000003     0.000060     YES
 RMS     Displacement     0.000001     0.000040     YES

Optimised molecule image

Jmol rotatable molecule

Log file: Media:NH3_OPT_LM.LOG

Optimised NH molecule

Important geometric parameters

Optimised bond distance and angle for NH₃
r(N-H)=1.02Â
θ(H-N-H)=105°

Vibrations

 Low frequencies ---   -5.6864   -3.6131   -3.6124    0.0017    0.0048    0.0162
 Low frequencies --- 1089.3674 1693.9284 1693.9284

Table of vibrations

Mode	1	2	3	4	5	6
Wave number (cm-1)	1089	1693	1693	3461	3590	3590
Symmetry	A1	E	E	A1	E	E
Intensity	145	14	14	1	0	0

NH₃ IR spectrum

Questions about the vibrations of NH₃

1. I would expect to see 3 vibrational modes from NH₃, as per the 3N-6 rule.

2. The computed spectrum of gaseous ammonia has 2 bands/peaks.

3. The modes at 1693 and 3589 cm^-1 are degenerate.

4. The modes at 3589 cm^-1 essentially have no intensity

5. There are fewer modes on the spectrum than predicted by the 3N-6 rule because one of the vibrational modes has such a low intensity that it is not visible on the IR spectrum.

6. Modes 1, 2, and 3 are bending vibrations and modes 4, 5, and 6 are stretching vibrations.

7. Mode 4 is known as the umbrella mode

8. The umbrella mode is so intense because it involves all three bonds between nitrogen and the hydrogens stretching all at the same time. The hydrogens get spread out and then pulled back in at a high frequency which corresponds to an intense peak on the spectrum.

Charge analysis

Table of charges

atom	charge
Nitrogen	-1.13
Hydrogen 1	0.38
Hydrogen 2	0.38
Hydrogen 3	0.38

Molecular orbitals

Snapshot of the real 2a₁ MO

Image of the LCAO for 2a₁

Project Molecule

Calculation Data

name of submitted log file	acetate_opt_lm.log
calculation method	RB3LYP
basis set	6-31G(d,p)
charge	-1
final energy	-228.5022
RMS gradient	0.000001
point group	Cs

Item table

Item               Value     Threshold  Converged?
 Maximum Force            0.000002     0.000015     YES
 RMS     Force            0.000001     0.000010     YES
 Maximum Displacement     0.000029     0.000060     YES
 RMS     Displacement     0.000009     0.000040     YES

Optimised bond lengths for C₂H₃O₂

bond	length
C-O	1.25 Â
C-C	1.58 Â
C-H	1.10 Â

Optimised bond angles for C₂H₃O₂

bond	θ (angle)
O-C-O	130 °
O-C-C	116 °
C-C-H	112 °
H-C-H	109 °

Image of optimised acetate molecule

Jmol rotatable molecule

Log file: Media:LM_C2H302_OPT.LOG

Optimised acetate molecule

Table of frequencies

Vibrations

Low frequencies ---   -6.3512   -4.5604   -1.8034    0.0010    0.0010    0.0011
 Low frequencies ---   28.4295  417.2706  601.5386

Table of vibrations

mode	wavenumber cm-1	symmetry	intensity
1	28	A"	0
2	417	A'	1
3	602	A"	4
4	612	A'	4
5	863	A'	72
6	985	A'	3
7	1021	A"	8
8	1318	A'	13
9	1374	A'	270
10	1481	A'	6
11	1495	A"	0
12	1756	A'	423
13	2998	A'	45
14	3061	A"	78
15	3084	A'	92

IR spectrum

IR analysis

1. what is the nature of the lowest energy vibration? The lowest energy vibration is at

Charge analysis

Image of charge distribution

Table of charges

atom	charge
C1	0.799
O2	-0.799
O3	-0.788
C4	-0.792
H5	0.201
H6	0.201
H7	0.197

Molecular orbital analysis

The core MOs are 1,2,3,4.

Image of molecular orbital 7

Occupied molecular orbitals that have pseudo-pi symmetry are orbitals 14, 11, and 6.

The oxygen atoms are the primary contributors to the highest occupied molecular orbital (HOMO). This is demonstrated in the image of molecular orbital 16 below.

The molecular orbital pictured below is MO 11.

The LCAO of molecular orbital 11: