Conformational Studies of 1-(2?-Hydroxythiobenzoyl)piperidine and 4-(2?-Hydroxythiobenzoyl)morpholine by High Resolution N.M.R. Spectroscopy

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Abstract
The 220 MHz 1H nmr spectra of the title compounds (1a) and (2a), respectively, at low temperature in CDCl3 solution are interpreted in terms of two interconverting chair forms with unequal populations (Ke = 1.17, δG° ∼70 cals/mole for 1a and Ke = 1.8, δG° ∼0.2 kcal/mole for 2a at −30°C). A strong intramolecular OH…S hydrogen bond in both compounds reduces the number of degrees of freedom of the bulky N-thiobenzoyl substituent, which nearly eclipses the equatorial α-CH2 hydrogen atoms in both comformations. Steric interactions between the 6′ phenyl proton and the hetero-ring α-CH2 protons trans to the thiocarbonyl group are different in the two conformations of la and 2a.

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