Simulation of spectra using Gaussian (WebMO.net) IR CH4 -------- R--CH4 ------- overlay the two --- split overlay IR CH3Cl ----- R--CH3Cl ---- overlay the two --- split overlay IR CH2Cl2 ---- R--CH2Cl2 --- overlay the two --- split overlay IR CHCl3 ----- R--CHCl3 ---- overlay the two --- split overlay IR CCl4 ------- R--CCl4 ------ overlay the two --- split overlay Toggle Grid Toggle Coordinates Reverse plot

The spectra are "hot-linked" to the molecular graphic display such that selecting a peak in the IR spectrum will cause a vibrational mode animation to be displayed.

The first exercise is to examine the applications of symmetry and group theory in the elucidation of the vibrational (Infrared and Raman) spectra of compounds. Several sample molecules and provided and you should calculate the number of Infrared and Raman active vibrations and compare their results with the experimental data given.

List of Character Tables for the various point groups

CH2Cl2 belongs to the C2v point group while CClH3 and CHCl3 belong to the C3v point group and CH4 and CCl4 belong to the Td point group.

Character table for C2v point group
E C2 (z) σv(xz) σv(yz) linear,
rotations
A1 1 1 1 1 z x2, y2, z2
A2 1 1 -1 -1 Rz xy
B1 1 -1 1 -1 x, Ry xz
B2 1 -1 -1 1 y, Rx yz
Character table for C3v point group
E 2C3 (z) v linear,
rotations
A1 1 1 1 z x2+y2, z2
A2 1 1 -1 Rz
E 2 -1 0 (x, y) (Rx, Ry) (x2-y2, xy) (xz, yz)

Character table for Td point group
E 8C3 3C2 6S4 d linear,
rotations
A1 1 1 1 1 1 x2+y2+z2
A2 1 1 1 -1 -1
E 2 -1 2 0 0 (2z2-x2-y2, x2-y2)
T1 3 0 -1 1 -1 (Rx, Ry, Rz)
T2 3 0 -1 -1 1 (x, y, z) (xy, xz, yz)

As an additional exercise it is possible to use the concept of Hooke's Law and reduced mass to predict the frequency of the C-D stretch based on the C-H stretch.

Acknowledgements
The simulated spectra were obtained using the WebMO interface to Gaussian. IR and Raman spectra were exported as uncompressed JCAMP-DX files and on-line computing times were less than 10 seconds for each isomer.