N-H or O-H
overtone of strong signal
Infrared Radiation is absorbed by molecules to create higher energy bonding vibrational states. The vibrational modes affected include stretching and bending modes, and require a change in the dipole moment of the molecule.
At right is a typical Infrared Spectrum, in which the frequency of radiation in units of reciprocal centimeters is plotted against the percentage of transmitted light. Each signal represents a complicated coupling of various vibrational modes resonating in that frequency range. Stretching frequencies for stronger bonds are typically easiest to identify, because they occur at higher frequencies.
Rather than try to identify each signal, the analysis of an Infrared Spectrum involves a systematic inspection of specific regions in the spectrum.
Acquaint yourself with as many examples of Infrared Spectra as you can, beginning with the examples given here: