The standard molar enthalpies of combustion and vaporization of three oxazolidines

Abstract

The compounds (4R, 5R)-3,4-dimethyl-5-phenyl-1,3-oxazolidine (OXA1), (4S, 5R)-3,4-dimethyl-5-phenyl-1,3-oxazolidine (OXA2) [Chemical Abstracts registry number 123618-06-4], and (4R, 5R)-2,2,3,4-tetramethyl-5-phenyl-oxazolidine (OXA3) [Chemical Abstracts registry number 141271-51-4] have been studied by oxygen bomb combustion calorimetry, and the vapor pressures were measured at different temperatures by a static method. On the basis of the experimental results, the standard molar enthalpies of formation of the liquid and gaseous compounds were determined. A summary of experimental and derived results at the temperatureT=298.15 K is shown below; where ΔcUm°(l), ΔcHm°(l), ΔfHm°(l), ΔlgHm°(l), and ΔfHm°(g) denote the standard molar energy of combustion, the standard molar enthalpy of combustion, the standard molar enthalpy of formation of the liquid compound, the standard molar enthalpy of vaporization, and the standard molar enthalpy of formation of the gaseous compound, respectively.The standard molar enthalpy of formation in the gaseous phase is decreased by 7.8 kJ·mol−1from compound OXA2 to OXA1. This quantity is attributed to the different configuration of the methyl group at the C-4 position of these compounds. In the envelope conformation, OXA2 has a nearlygaucheinteraction between the phenyl and methyl substituents, while OXA1 has a nearlyanti-interaction between the same substituents. In addition, with the experimental results for compounds OXA1 and OXA3, the group contribution terms to the standard molar enthalpies of formation of the gaseous compounds for the molecular groups {C-(O)(N)(H)2} and {C-(O)(N)(C)2} were derived as −104.5 kJ·mol−1and −118.8 kJ·mol−1, respectively.