S. Kahn, W. Hehre
Feb 1, 1987
Citations
0
Influential Citations
34
Citations
Journal
Journal of the American Chemical Society
Abstract
Conformational energy profiles for 3-buten-2-ol and 2-methoxy-3-butene, obtained from a uniform level of nonempirical molecular orbital theory, are qualitatively similar; the differences between the two appear to arise primarily because of steric interactions. The lowest energy conformers for both position the OH (OR) group directly over the double bond, casting doubt on the previously advanced interpretation that the equilibrium conformation of the allylic alcohol is directed in part by hydrogen bonding between the hydroxylic hydrogen and the ..pi.. bond. It suggests instead that the conformational biases in both the alcohol and ether are influenced primarily by minimization of oxygen lone pair-..pi.. bond repulsion. Electrostatic potentials indicate a preference for electrophilic attack anti to the OR group in the high-abundance but low-reactivity conformers of 2-methoxy-3-butene and syn to OR in the less abundant but much more reactive conformers, the same preferences as have previously been noted in 3-buten-2-ol. Given that electrophilic addition to allylic alcohols and ethers generally occurs syn to the OH (OR) functionality, the results of the theory support a notion that the overall reaction stereochemistry in these systems is influenced more by relative conformer reactivity than by relative abundance.