Quantum Chemical Study of the Preferred Conformations, Molecular Geometries, and Relative Thermodynamic Stabilities of 2-Substituted 4-Methylene-1,3-Dioxolanes and 4-Methyl-1,3-Dioxoles

摘要

The preferred conformations, molecular geometries, and relative stabilities of carbon-carbon doublebond exo-endo isomeric 2-substituted 4-methylene-1,3-dioxolanes (a) and 4-methyl-1,3-dioxoles (b) have been studied by DFT calculations at the B3LYP/6-31G~* level of theory. The main interest of this work was devoted to the contribution of alkoxy substituents on the relative thermodynamic stabilities of these isomeric unsaturated acetals. Comparison of the computational data with previous experimental findings shows both the enthalpies and entropies of the a -> b isomerization to be accurately predictably by the DFT calculations. Most importantly, the good agreement between experiment and theory proved also to be applicable to the previously observed unexpectedly large effect of 2-alkoxy substitution on the isomer equilibria.