Question

Why is infrared spectroscopy used in organic chemistry?

Answer 1

Because it CAN be useful; especially in the identification of `C=O` and `C-D` `(""^2H-C)` bonds.

Explanation:

I can remember some of the older organic profs at university, who were remarkably proficient in the identification and interpretation of IR spectra. When I asked them why they were so good, they said at the time the IR spectrometers became available (the 1960s and 1970s) they were the ONLY instrumental method of characterization, so they had no other choice but to become expert in the technique.

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-=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.