CONFORMATIONAL-ANALYSIS OF 2,3-DISUBSITITUED 1,4-DITHIANES BY NMR-SPECTROSCOPY AND MMX CALCULATIONS

The conformer populations for trans- and cis-2,3-disubstituted 1,4-dit hianes have been determined by H-1 and C-13 NMR spectroscopy and calcu lated by molecular mechanis (MMX). The CH(2)X-substituents demonstrate the strong preference for axial position. The remarkable difference o riginating from intramolecular steric interactions has been observed b etween tow trans-dialkyl derivatives: the trans-2,3-dimethyl-1,4-dithi ane is predominantly equatorial whereas trans-2,3-dipropyl-1,4-dithian e prefers diaxial conformation. The properties of cis-2,3-dipropyl-1,4 -dithiane are also unusual: its ring interconversion is unexpectedly s low (Delta G(not equal) = 11.2 kcal mol(-1) at 260K).