The First Direct Experimental Determination of Strain in Neutral and Protonated 2-Azetidinone

Abstract

The standard molar enthalpies of combustion, sublimation, and formation in the crystalline and gaseous state at a temperature of 298.15 K have been experimentally determined for the title compound (1) and for N-methylacetamide (2). These results have been combined with their gas-phase proton affinities to yield the standard enthalpies of formation of the species 1H+(g) and 2H+(g). These magnitudes have also been computed at the G2(MP2) level. The agreement between experimental and theoretical results is very good. This information has been used to determine the strain in the neutral and protonated β-lactam ring in the absence of solvent.