Analysis of the Potential Energy Surface of 1,3-Dioxane and Its Protonated Form

Abstract

1,3-Dioxanes are practically important oxygencontaining heteroanalogs of cyclohexane. Protonation of these compounds, as well as of other 1,3- and 1,3,2-heterocycles, gives cyclic oxonium ions. The latter are formed as intermediates in numerous acidcatalyzed heterolytic reactions involving cyclic boron acid esters, 1,3-dioxa-2-silacyclohexanes, and cyclic acetals, which lead to formation of esters, 1,3-diols, and other valuable products of organic and petrochemical synthesis [1–4]. However, oxonium ions could be detected experimentally only at temperatures below –50°C, which strongly restricts the applicability of physical methods for studying fine details of their structure; therefore, such information is lacking in the literature. We thought it reasonable to examine the structure and conformational behavior of such species by quantum-chemical methods. The present communication reports on the results of comparative study of the potential energy surfaces (PES) of unsubstituted 1,3-dioxane (I) and its protonated form II in the gas phase in terms of the STO-3G and 6-31G** nonempirical methods. The calculations were performed using HyperChem software package [5].