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NH3 Structural Information

Vibrations of NH3

N-H bond length: 1.02 Å

H-N-H bond angle: 106°

Structure: trigonal pyramidal

NH3

Gaussian Optimisation

Calculation method: RB3LYP

Basis set: 6-31H(d.p)

Final energy E in atomic units: -56.55776873 au

The point group of NH3: C3V

Display Vibrations

      
         Item               Value     Threshold  Converged? 
Maximum  Force            0.000004     0.000450     YES
 RMS     Force            0.000004     0.000300     YES
 Maximum Displacement     0.000072     0.001800     YES
 RMS     Displacement     0.000035     0.001200     YES

The optimisation file is linked to File:HHE NH3 OPTF-POP.LOG

Wavenumber, Symmetry and Intensity of Vibrations

Number of modes using 3N-6: 3×4-6=6

Degenerate modes: 1694 cm-1, 3590 cm-1

Bending: 1090, 1694 cm-1

Stretching: 3461, 3590 cm-1

Highly symmetric: 3461 cm-1

Umbrella mode: 1090 cm-1

IR bands: 2 bands expected as two of them are degenerate and 3 of them are of 0 or negligible intensity.

Vibrations
wavenumber (cm-1) 1090 1694 1694 3461 3590 3590
symmetry A1 E E A1 E E
intensity (arbitrary units) 145 14 14 1 0 0
image

Charge Analysis

N is expected to be negative and H is expected to be positive because N is more electronegative than H and pulls electrons more towards N itself.
Charges on NH3

N2 Structural Information

Vibration of N2

Bond length: 1.11 Å

Structure: linear

N2

Gaussian Optimisation

Calculation method: RB3LYP

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

Final energy E in atomic units: -109.52412868 au

The point group of NH3: D∞h

Display Vibrations

         Item                Value    Threshold  Converged?
 Maximum Force            0.000145     0.000450     YES
 RMS     Force            0.000145     0.000300     YES
 Maximum Displacement     0.000045     0.001800     YES
 RMS     Displacement     0.000064     0.001200     YES

The optimisation file is linked to File:HHE N2 OPTF POP.LOG

Wavenumber, Symmetry and Intensity of Vibrations

Number of modes using 3N-5: 3×2-5=1

Degenerate modes: 0

Bending: 0

Stretching: 1

IR bands:0 because there is no change in dipole moment of the molecule in the stretching mode

Vibrations
wavenumber (cm-1) 2457
symmetry SGG
intensity (arbitrary units) 0
image

Charge Analysis

Charge on N2

The charges are expected to be zero because there is no difference in electronegativities between the 2 atoms.

H2 Structural Information

Vibration of H2

Bond length: 0.74 Å

Structure: linear

H2

Gaussian Optimisation

Calculation method: RB3LYP

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

Final energy E in atomic units: -1.17853930 au

Point group: D∞h

Display vibrations

         Item                Value    Threshold  Converged?
 Maximum Force            0.000211     0.000450     YES
 RMS     Force            0.000211     0.000300     YES
 Maximum Displacement     0.000278     0.001800     YES
 RMS     Displacement     0.000393     0.001200     YES

The optimisation file is linked to File:HHE H2 OPTF POP.LOG

Wavenumber, Symmetry and Intensity of Vibrations

Number of modes using 3N-5: 3×2-5=1

Degenerate modes: 0

Bending: 0

Stretching: 1

IR bands: 0 because there is no change in dipole moment of the molecule in the stretching mode

Vibrations
wavenumber (cm-1) 4461
symmetry SGG
intensity (arbitrary units) 0
image

Charge Analysis

Charge on H2

The charges are expected to be zero because there is no difference in electronegativities between the 2 atoms.

Transition Metal Complex

Identifier: JISZOA[1]

Calculated bond length: 0.74 Å

Bond length in complex: 1.03 Å

In this complex, H2 donates electrons to the central metal atom and the bond energy of H2 is lower and therefore the bond length is longer.[1]

Haber-Bosch Process

E(NH3)= -56.5577687 au

2*E(NH3)= -113.1155374 au

E(N2)= -109.5241287 au

E(H2)= -1.1785393 au

3*E(H2)= -3.5356179 au

ΔE=2*E(NH3)-[E(N2)+3*E(H2)]= -0.0557909 au

= -146.8 kJmol-1

The ammonia product is more stable because the reaction is exothermic.

HCN Structural Information

Vibrations of HCN

H-N bond length: 1.07 Å

C≡N bond length: 1.16 Å

H-C≡N bond angle: 180 °

HCN

Gaussian Optimisation

Calculation method: RB3LYP

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

Final energy E in atomic units: -93.42458151 au

The point group of NH3: C∞v

Display vibrations


         Item               Value     Threshold  Converged?
 Maximum Force            0.000179     0.000450     YES
 RMS     Force            0.000094     0.000300     YES
 Maximum Displacement     0.000145     0.001800     YES
 RMS     Displacement     0.000101     0.001200     YES

The optimisation file is linked to File:HHE HCN OPTF POP.LOG

Wavenumber, Symmetry and Intensity of Vibrations

Number of modes using 3N-5: 3×3-5=4

Degenerate modes: 769 cm-1

Bending: 769 cm-1

Stretching: 2214 and 3476 cm-1

IR bands: 3 because all vibrations cause a change in dipole moment and 2 of them are degenerate.

Vibrations
wavenumber (cm-1) 769 769 2214 3476
symmetry PI PI SG SG
intensity (arbitrary units) 35 35 2 57
image

Charge Analysis

Charges on HCN

Nitrogen is the most electronegative atom of all three atoms and it is expected to have a negative charge. Carbon is more electronegative than hydrogen and therefore the charge on carbon is less positive than that on hydrogen.

Molecular Orbitals

Orbital 1

Energy:-14.36052 au

This orbital is the core 1s orbital on N which is too deep in energy to be involved in bonding. Therefore it does not contribute to the bonding in the molecule. It is occupied by 2 electrons.

Orbital 2

Energy:-10.24613 au

This is the core 1s orbital on C which is also too deep in energy to be involved in bonding. This atomic orbital does not contribute to the bonding in the molecule either. This orbital is also occupied by 2 electrons.

Orbital 3

Energy: -0.91992 au

This is a bonding molecular orbital composed of 2s atomic orbitals on N and C and a 1s atomic orbital on H. It is involved in bonding as its energy is not as deep in energy as the last 2 orbitals. All atomic orbitals are in phase and the electron density therefore encompasses the whole molecule with no nodal plane. It is occupied by 2 electrons.

Orbital 7

Energy: -0.35936 au

This is the bonding molecular orbital made up of 2py atomic orbitals on N and C. The 2 orbitals combine in phase and produce a bonding pi orbital. The hydrogen 1s atomic orbital is not involved as there is a nodal plane across the bond. It is also the HOMO, which is filled with 2 electrons.

Orbital 8

Energy: 0.01927 au

This is the LUMO and it is an antibonding orbital. It is formed by the 2px atomic orbitals on N and C, the hydrogen 1s atomic orbital is not involved for the same reason stated above. This molecular antibonding orbital is orthogonal to the one above as the px and py are orthogonal to each other. It is positioned this way just to be seen more clearly. It is empty and therefore does not contribute to the bonding in the molecule.

Independent Work

CH4 Structural Information

C-H bond length: 1.09 Å

H-C-H bond angle: 109°

Structure: tetrahedral

CH4

Gaussian Optimisation

Calculation method: RB3LYP

Basis set: 6-31H(d.p)

Final energy E in atomic units: -40.52401404 au

The point group of CH4: Td

Display Vibrations


         Item               Value     Threshold  Converged?
 Maximum Force            0.000063     0.000450     YES
 RMS     Force            0.000034     0.000300     YES
 Maximum Displacement     0.000179     0.001800     YES
 RMS     Displacement     0.000095     0.001200     YES

The optimisation file is linked to File:HHE CH4 OPTF.LOG

Wavenumber, Symmetry and Intensity of Vibrations

Number of modes using 3N-6: 3×5-6=9

Degenerate modes: 1356 cm-1, 1579 cm-1, 3162 cm-1

Bending: 1356 cm-1, 1579 cm-1

Stretching: 3046cm-1, 3162 cm-1

IR bands: 2 as 5 of them are degenerate and 3 of them are of 0 intensity.

Vibrations of CH4
Vibrations
wavenumber (cm-1) 1356 1356 1356 3046 1579 1579 3162 3161 3162
symmetry T2 T2 T2 A1 E E T2 T2 T2
intensity (arbitrary units) 14 14 14 0 0 0 25 25 25
image

Charge Analysis

Charges on CH4
C is expected to be negative and H is expected to be positive because C is more electronegative than H and pulls electrons more towards C itself.

Reference

  1. Chaudret, B., Chung, G., Eisenstein, O., Jackson, S., Lahoz, F. and Lopez, J. (1991). Journal of the American Chemical Society, 113(6), pp.2314-2316.

Marking

Note: All grades and comments are provisional and subject to change until your grades are officially returned via blackboard. Please do not contact anyone about anything to do with the marking of this lab until you have received your grade from blackboard.

Wiki structure and presentation 1/1

Is your wiki page clear and easy to follow, with consistent formatting?

YES

Do you effectively use tables, figures and subheadings to communicate your work?

YES

NH3 1/1

Have you completed the calculation and given a link to the file?

YES

Have you included summary and item tables in your wiki?

YES

Have you included a 3d jmol file or an image of the finished structure?

YES

Have you included the bond lengths and angles asked for?

YES

Have you included the “display vibrations” table?

YES

Have you added a table to your wiki listing the wavenumber and intensity of each vibration?

YES

Did you do the optional extra of adding images of the vibrations?

YES

Have you included answers to the questions about vibrations and charges in the lab script?

YES

N2 and H2 0.5/0.5

Have you completed the calculations and included all relevant information? (summary, item table, structural information, jmol image, vibrations and charges)

YES

Crystal structure comparison 0.5/0.5

Have you included a link to a structure from the CCDC that includes a coordinated N2 or H2 molecule?

YES

Have you compared your optimised bond distance to the crystal structure bond distance?

YES

Haber-Bosch reaction energy calculation 1/1

Have you correctly calculated the energies asked for? ΔE=2*E(NH3)-[E(N2)+3*E(H2)]

YES

Have you reported your answers to the correct number of decimal places?

YES

Do your energies have the correct +/- sign?

YES

Have you answered the question, Identify which is more stable the gaseous reactants or the ammonia product?

YES

Your choice of small molecule 4/5

Have you completed the calculation and included all relevant information?

YES

Have you added information about MOs and charges on atoms?

YES

The information you have given I this sections are correct! MO 1 and 2 could have been labelled as non-bonding but you explained the influence on bonding correctly. You could have explained the relative MO energies (e.g. comparing number of nodes, electronegativities etc.)

Independence 1/1

If you have finished everything else and have spare time in the lab you could:

Check one of your results against the literature, or

Do an extra calculation on another small molecule, or

YES

Do some deeper analysis on your results so far