Ruth

Lab 2

Me₃NH-Cl Ion Pair

Calculation Data

name of submitted log file	TR ME3NH-CL OPTF.LOG
molecule	Me3NH+-Cl-
method	RB3LYP
basis set	3-21G
final energy	-632.16208 Hartree
RMS gradient	1.8962e-05 Hartree/Bohr
point group	Gaussian output: C1 (note: actual is C3v)

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Logfile and Relevant Excerpts

Media:TR ME3NH-CL OPTF.LOG

         Item               Value     Threshold  Converged?
 Maximum Force            0.000029     0.000450     YES
 RMS     Force            0.000010     0.000300     YES
 Maximum Displacement     0.002276     0.001800     NO 
 RMS     Displacement     0.000572     0.001200     YES

 Full mass-weighted force constant matrix:
 Low frequencies ---   -9.8211    0.0025    0.0030    0.0032    2.7858    4.2211
 Low frequencies ---   55.2435   56.5270  190.4173

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Optimised Molecule

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Scan

TODO: report quality graph n explanation

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NH₃-BH₃ Molecule

Calculation Data

name of submitted log file	TR_NH3-BH3_OPTF_POP.LOG
molecule	NH3-BH3
method	RB3LYP
basis set	6-31G(d,p)
final energy	-83.224689 Hartree
RMS gradient	1.182e-06 Hartree/Bohr
point group	Gaussian output: C3v (note: the actual point group is D3d)

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Logfile and Relevant Excerpts

Media:TR_NH3-BH3_OPTF_POP.LOG

         Item               Value     Threshold  Converged?
 Maximum Force            0.000002     0.000015     YES
 RMS     Force            0.000001     0.000010     YES
 Maximum Displacement     0.000017     0.000060     YES
 RMS     Displacement     0.000008     0.000040     YES

 Full mass-weighted force constant matrix:
 Low frequencies ---   -5.4404   -0.3252   -0.0481   -0.0011    1.1254    1.2097
 Low frequencies ---  263.2923  632.9711  638.4650

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Optimised Molecule

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Association Energy

For the formation reaction shown below, we can calculate the association energy by subtracting the total energy of the reactants by the energy of the adduct: NH₃ + BH₃ → NH₃BH₃

That is, we apply ΔE = E(NH₃BH₃) - [E(NH₃) + E(BH₃)].

E(NH3BH3)	-83.224689 Hartree
E(NH3)	-56.557769 Hartree
E(BH3)	-26.615324 Hartree
ΔE	-0.051596 Hartree, -135 kJ/mol

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BH₃ Molecule

Calculation Data

name of submitted log file	TR_BH3_OPTF_POP.LOG
molecule	BH3
method	RB3LYP
basis set	6-31G(d,p)
final energy	-26.615324 Hartree
RMS gradient	2.114e-06 Hartree/Bohr
point group	D3h

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Logfile and Relevant Excerpts

Media:TR_BH3_OPTF_POP.LOG

         Item               Value     Threshold  Converged?
 Maximum Force            0.000004     0.000015     YES
 RMS     Force            0.000003     0.000010     YES
 Maximum Displacement     0.000017     0.000060     YES
 RMS     Displacement     0.000011     0.000040     YES

 Full mass-weighted force constant matrix:
 Low frequencies ---  -11.6940  -11.6861   -6.5543    0.0007    0.0280    0.4289
 Low frequencies --- 1162.9745 1213.1390 1213.1392

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Optimised Molecule

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Lab 1

Lab1 Marking

You did a great job especially with the formatting. However, you missed to include the charge range, and don't forget to consider the accuracy to which you report your data the next time. If you have any queries, please contact Prof. Hunt.

NH₃ Molecule

Calculation Data

name of submitted log file	TR_NH3_OPTF_POP.LOG
molecule	NH3
method	RB3LYP
basis set	6-31G(d,p)
final energy	-56.557769 Hartree
RMS gradient	1.53e-07 Hartree/Bohr
point group	C3v

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Logfile and Relevant Excerpts

Media:TR_NH3_OPTF_POP.LOG

         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

 Full mass-weighted force constant matrix:
 Low frequencies ---   -5.6864   -3.6131   -3.6124    0.0017    0.0048    0.0162
 Low frequencies --- 1089.3674 1693.9284 1693.9284

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Optimised Molecule

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Geometric Data

Optimised bond angles and distances

r(N-H)	1.02 Â
θ(H-N-H)	106°

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Vibrational Data

mode	1	2	3	4	5	6
wavenumber (cm-1)	1089	1694	1694	3461	3590	3590
symmetry	A1	E	E	A1	E	E
intensity (arbitrary units)	145	14	14	1	0	0

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Atomic Charges

	Atomic Charge (e)
N	-1.13
H	0.38

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Molecular Orbitals

Frontier MOs

	Energy (Hartree)	GaussView visualisation
LUMO	0.07985
HOMO	-0.25318

Project Molecule: cis-N₂F₂

Calculation Data

name of submitted log file	TR_N2F2_OPTF_POP.LOG
molecule	cis-N2F2
method	RB3LYP
basis set	6-31G(d,p)
final energy	-309.01241 Hartree
RMS gradient	3.17e-07 Hartree/Bohr
point group	C2v

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Logfile and Relevant Excerpts

Media:TR_N2F2_OPTF_POP.LOG

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

 Full mass-weighted force constant matrix:
 Low frequencies ---   -0.0019    0.0002    0.0008    3.2225    4.3532    5.1001
 Low frequencies ---  347.8772  561.2472  771.6105

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Optimised Molecule

Note: N-F bonds are not drawn here by GaussView because r(N-F) in the final optimised structure (1.39 Â) exceeds the software's distance threshold for visualisation.

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Geometric Data

Optimised bond angles and distances

r(N=N)	1.23 Â
r(N-F)	1.39 Â
θ(N=N-F)	114°

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Vibrational Data

mode	1	2	3	4	5	6
wavenumber (cm-1)	348	561	772	949	987	1637
symmetry	A1	A2	B2	A1	B2	A1
intensity (arbitrary units)	1	0	75	75	81	21

Discussion

Given cis-N₂F₂ is non-linear, we expect it to have 3N-6 vibrational modes where N=4, i.e. 6 vibrations. Although 6 vibrational modes are indeed calculated, only 4 are visible in the simulated IR spectrum since the 2 lowest energy modes are symmetric bending vibrations which do not induce a change in dipole moment and thus are IR-inactive. Raman spectroscopy would instead be required to investigate those 2 modes. As a general trend, notice that the lower energy vibrational modes are 'bends', whereas the higher energy modes are 'stretches' (e.g. the asymmetric N-F stretch at 772 cm^-1). Indeed, the highest energy mode is a stretching vibration of the N=N double bond, which is not unexpected given the higher force constant of the double bond compared to the single bonds. Notice the orange dipole derivative unit vector of this mode shown in the animation below, indicating the change in dipole moment that allows the mode to be IR active.

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Atomic Charges

	Atomic Charge (e)
N	0.215
F	-0.215

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Molecular Orbitals

Frontier MOs

	Energy (Hartree)	GaussView visualisation
LUMO	-0.08646
HOMO	-0.37454

9^th MO

GaussView visualisation	LCAO diagram

Discussion

Of the 16 occupied MOs, the 4 lowest energy ones are core orbital MOs derived from the bonding-antibonding pairs of 1s orbitals for the 2 N atoms, and the 2 F atoms. These are largely irrelevant for investigating the reactivity and other properties of the molecule compared to non-core MOs, e.g. the HOMO and LUMO. These frontier orbitals can allow us to make some predictions. Firstly, the HOMO-LUMO gap corresponds to light of about 158 nm (deep UV) so cis-N₂F₂ is likely colourless. Secondly, the negative energy of the LUMO (-0.08646 E_h) means that an electron would be lower in energy when occupying it compared to being free, a surprising result given the usual Lewis base behaviour of N, possibly caused by the positive atomic charge on the N atoms (see above).