...... whereas, #"IR spectroscopy"# examines molecular transitions.
The most common (and most sensitive) form of #"NMR spectroscopy"# is #""^1"H"# #"NMR spectroscopy"#. And this examines nuclear transitions. A proton, an hydrogen nucleus, has spin, and has charge. And therefore it is a magnet. And thus it can be spin up or spin down with respect to an applied magnetic field, and the chemist can examine the magnetic environment of the proton in various molecules. Since the proton is present in quantity in all organic compounds, #""^1"H NMR spectroscopy"# is a very widely used, and HIGHLY diagnostic tool of chemical analysis.
On the other hand, #"IR spectroscopy"# examines molecular transitions; how a given bond between 2 atoms absorbs IR radiation. IR spectroscopy is very much a sporting means of chemical analysis in that an IR spectrum conveys MUCH less useful information than an NMR spectrum, and requires much more supposition, and analysis.
