An infrared study of the tautomerism of chlorinated 2-pyridinols isolated in an argon matrix

The infrared spectra of 3-, 4-, 5- and 6-monochloro-, 3,5,6-trichloro-2-pyridinols (pyridones), and of the unsubstituted 2-pyridinol isolated in a low temperature (20°K) argon matrix were studied. The results indicate that the enol/keto ratio for the isolated pyridinols decreases according to the position of the chlorine atom(s) on the pyridine ring; i.e., 3,5,6-trichloro >-6 > 5 > 4 > 3 monochloro-2-pyridinols. 3,5,6-Trichloro-2-pyridinol exists predominantly in the enol form.