Cyclic ketene acetals and ketene aminals belong to a class of organic molecules characterized by a nucleophilic exo-methylene carbon attached to a carbon with two adjacent highly electronegative atoms.   In the case of ketene acetals these two atoms are oxygen, and in ketene aminals these are nitrogen.  Such systems have been shown to react with a large number of mono- and dielectrophiles to yield a rich variety of organic reactions including tandem cyclizations, arylvinyl ester formation, new heterocyclic ring and fused ring formation, ring-retained polymerizations, and stereoselective radical cyclizations.   Since the stability of the ring of these ketene acetals and aminals are important in these reactions, the conventional strain energies for representative systems are determined within the isodesmic, homodesmotic, and hyperhomodesmotic models to investigate the role the external double bond plays in the ring strain of these heterocyclic systems.  Specifically, the conventional strain energies of 2-methylene-[1,3]dioxetane, 2-methylene-[1,3]diazetidine, 2-methylene-[1,3]dioxolane, 2-methylene-imidazolidine, 2-methylene-[1,3]oxazetidine, and 2-methylene-oxazolidine are compared to those of [1,3]dioxetane, [1,3]diazetidine, [1,3]dioxolane, imidazolidine, [1,3]oxazetidine, and [1,3] oxazolidine.<br/>Optimum equilibrium geometries, harmonic vibrational frequencies, and corresponding electronic energies are computed for all pertinent molecular systems using SCF theory, second-order perturbation theory (MP2), and density functional theory (DFT). The DFT functionals employed are Becke’s three-parameter hybrid functional using the LYP correlation functional and the M06-2X high nonlocality hybrid functional from Thular and Zhao.  The basis sets employed are Dunning and coworkers’ correlation consistent basis sets: cc-pVDZ, cc-pVTZ, and cc-pVQZ.<br/>

Conventional strain energy in ketene acetals and ketene aminals

253rd National Meeting (2017)

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