Conformational analysis of 3,4-epoxytetrahydropyran by n.m.r. spectroscopy

The conformational equilibrium of the title compound has been determined by correlating its n.m.r. parameters with those of its 2,2,6,6-tetradeuterio derivative and trans- and cis-2-tert-butyl-4,5-epoxytetrahydropyran. The high preference (ΔG ～ ?0.8 kcal/mol) for the half-chair conformation in which the pyranoid oxygen is furthest from the oxirane oxygen atom can be interpreted in terms of electrostatic interactions between the two oxygen atoms.