Energies of minima and TS as well as characteristic NMR chemical shifts are
reported for the parent unsaturated phospho-organic molecules with CP2 bac
kbone. Within the 14 relevant isomers of CH4P2, the two most stable structu
res are 1,2-diphospha-1-propene, 3, and diphosphirane (cyclo-CH2(PH)(2), 1,
E-rel = 8 kJ/mol). The relative energies in kJ/mol at MP2/6-31G(d,p) are 8
4 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 po
tential. intermediate products (PH-CH2-PH, PH-PH-CH2, and cyclo-CH2-PH2-P)
of diphosphirane rearrangements have the relative energies 182, 157, and 15
8 kJ/mol, respectively, and other minima were found to have E-rel between 2
87 and 322 kJ/mol. Rupture of endocyclic bonds of In displays a preference
for opening the P-C bond toward the CH2-PH-PH structure, which is stabilize
d by allyl conjugation. The lowest energy pathway for isomerization of 1 ha
s a barrier of 213 kJ/mol and goes via the intermediate cyclo-(CH2)(PH2)(P)
toward PH2-P=CH2. The calculated energy barriers of CH3-P=PH, 3, indicate
that this isomer should be kinetically stable as isolated molecule.