Question

when would Ir not be useful

whhat chemicals would effect ir spetum when is a bad idea to us it ?

Answer 1

IR Spectroscopy provides information on transition between vibrational and rotational energy levels in molecules. Different polar bonds give transtion in different IR regions thus, helping in detection of functional group in the organic compounds.

A molecule will be IR active only when there is a change in dipole moment during a vibrational transition.

So, IR spectrum of compounds or molecules having zero dipole like homodiatomic molecules (for ex. H2, O2, Cl2, etc.) cannot be dectected. Because the bonds in such molecules are non-polar resulting into no change in dipole moment during transition.