# Why is infrared spectroscopy used in organic chemistry?

Because it CAN be useful; especially in the identification of $C = O$ and $C - D$ (""^2H-C) bonds.
Of course, carbonyl bonds ($C = O$) are very easy to identify in IR spectra, so IR spectroscopy is an excellent means to monitor oxidation reactions, or to characterize $M - C \equiv O$ species.
One use of IR spectroscopy involves the replacement of an active hydrogen on the molecule by the deuterium nucleus - these are identical chemically, but the increased mass of the of the ""^2H nucleus means that the $C - D$ or $M - D$ stretch will occur at a predictably lower frequency, and allow assignment of the $M - H$ stretch. So isotopic substitution of an element hydrogen bond is an area where IR spectroscopy is still will widely used.