Thermochemistry of Oxabicyclo-Heptanes, Oxabicyclo-Heptene: Enthalpy of Formation, Entropy, Heat Capacity, and Group Additivity

Abstract

Thermochemical properties, ΔfH°(298), S°(298) and [Cp°(T)] (10K⩽T⩽5000) of the seven target bicyclic epoxides are calculated using the density functional methods. Molecular structures and vibration frequencies for 6-oxabicyclo[3.1.0]hexane, 7-oxabicyclo[4.1.0]heptane, 8-oxabicyclo[5.1.0]octane, 7-oxabicyclo[2.2.1]heptane, endo-2-methyl-7-oxabicyclo[2.2.1]heptane, exo-2-methyl-7-oxabicyclo[2.2.1]heptane and 7-oxabicyclo[4.1.0]hept-2,4-ene are calculated at the B3LYP∕6-31G(d,p) level of theory. Enthalpies of formation are determined at B3LYP∕6-31G(d,p) calculation level using isodesmic and homodesmic working reactions with the ΔrxnH° and known enthalpies of reference species in each of three different work reactions. Entropy (298) and heat capacity [Cp°(T)] values along with Benson Group additivity parameters are reported for each ring system. Data previously reported on oxybicyclo-epoxides are summarized.