How the Fourteen Most Stable CH4P2 Isomers InterconvertAn ab Initio/NMR Study

Abstract

Energies of minima and TS as well as characteristic NMR chemical shifts are reported for the parent unsaturated phospho-organic molecules with CP2 backbone. Within the 14 relevant isomers of CH4P2, the two most stable structures are 1,2-diphospha-l-propene, 3, and diphosphirane (cyclo-CH2(PH)2, 1, Erel = 8 kJ/mol). The relative energies in kJ/mol at MP2/6-31G(d,p) are 84 for 1,3-diphospha-2-propene, 54 for 1,2-diphospha-2-propene, and for the phosphinidenes, they are 63 (P−PH−CH3) and 102 (P−CH2−PH2). Although the potential intermediate products (PH−CH2−PH, PH−PH−CH2, and cyclo-CH2−PH2−P) of diphosphirane rearrangements have the relative energies 182, 157, and 158 kJ/mol, respectively, and other minima were found to have Erel between 287 and 322 kJ/mol. Rupture of endocyclic bonds of 1a displays a preference for opening the P−C bond toward the CH2−PH−PH structure, which is stabilized by allyl conjugation. The lowest energy pathway for isomerization of 1 has a barrier of 213 kJ/mol and goes via the interme...