Consider the vibrational mode that corresponds to the boat-like bending of a benzene ring. Is it (i) Infrared active? (ii) Raman active?
This question was asked in an assignment in my college. However, all we've been taught is how to distinguish functional groups in organic molecules using characteristic IR frequencies, nothing else. From this I can tell that the C=O stretch in a carbonyl compound, for example, is IR-active. But how do we determine this for any molecule and any normal mode in general?