Isomers of diphosphetane obviously include 1,2-diphosphetane and 1,3-diphosphetane. In addition, each of these have cis as well as trans isomers with respect to the hydrogens bonded to the two phosphorus atoms in each ring. Additional conformations are possible because these hydrogens may be axial or equatorial. Specifically, both axial and equatorial conformations exist for trans-1,2-diphosphetane and for cis-1,3-diphosphetane. Only one conformation can exist for cis-1,2-diphosphetane and for trans-1,3-diphosphetane because in these two systems one of the hydrogens must be axial while the other must be equatorial. Optimum equilibrium geometries, harmonic vibrational frequencies, and corresponding electronic energies are computed for all six systems using self-consistent field (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. In addition to simply comparing the relative energies, the electronic energies are broken down into the nuclear-electron attraction part and the two repulsive components, the nuclear-nuclear repulsion and the electron-electron repulsion, to gain additional insight into why one conformation is more stable than another.

Analysis of the relative energies of isomers of diphosphetane in terms of attractive versus repulsive forces

255th National Meeting (2018)

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