The conventional strain energies of 1,2-diazetidine, 1,3-diazetidine, 1,2-diphosphetane, and 1,3-diphosphetane are determined within the isodesmic, homodesmotic, and hyperhomodesmotic models.  Both cis and trans isomers of each of these systems are considered.  Optimum equilibrium geometries, harmonic vibrational frequencies, and corresponding electronic energies and zero-point vibrational energies are computed for all pertinent molecular systems using SCF theory, second-order perturbation theory, and density functional theory and employing three correlation consistent basis sets of Dunning and coworkers: cc-pVDZ, cc-pVTZ, and cc-pVQZ.  Single point fourth-order perturbation theory, CCSD, and CCSD(T) calculations employing the cc-pVTZ and the cc-pVQZ basis sets are computed using the MP2/cc-pVTZ and MP2/cc-pVQZ optimized geometries, respectfully, to ascertain the contribution of higher-order correlation.  Three DFT functionals, B3LYP, wB97XD, and M06-2X, are considered to determine if they can yield results similar to those obtained at the CCSD(T) level.  We gratefully acknowledge support from the NSF (EPS-0903787) and the W.M. Keck Foundation.

Conventional strain energies of the diazetidines and the diphosphetanes

245th National Meeting (2013)

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