This is concerned
with the molecular vibrations of the molecule which yields important
information about the molecular formula, and the molecular shape. The
information can be used in both a qualitative fashion, (e.g. the molecule
contains a carbonyl group) or a quantitative fashion (e.g. the molecule
has three CO ligands and C3v point group). Below are some
vibrational mode is active if there is a change in the dipole
moment during the vibration.
vibrational mode is active if there is a change in the polarizability
during the vibration.
Specific functional groups, or ligands are often found
in characteristic regions of the IR spectrum, a few of these are given
below. All of the information about characteristic frequencies that
you have learnt about in Organic Chemistry courses for identifying carbonyl,
O-H, carboxylic acid groups etc is, of course, still relevant. Many
ligands contain these groups. Some of the most important characteristic
frequencies are given below.
Nitrides and Halides
thiocyanate and selenocyanate ligands
This predicts the vibrations of specific functional groups, or ligands
there are in a molecule.
This is calculated
by reduction, which can be performed by eye
or the reduction formula. The reduction
is performed after calculating the number of bond that remain unshifted
by the operations performed on it. These are a sub set of the molecule
and at the full molecule.
representational spectra is available