Vibrations of Polyatomic Molecules:

You would agree that the vibration spectrum of a polyatomic molecule along with a number of bonds is expected to be quite complex. Indeed, the IR spectrum for a molecule of a reasonable size is quite complex and it is almost impossible (and mostly not desirable) to interpret all the signals obtained. Therefore, with a little understanding of the probable vibration modes, their IR activity (or otherwise) and the concept of characteristic group frequencies we could make sufficient leads into deciphering the structural complexities of the molecules. Now let us try to make an attempt to have that understanding.