Semiempirical MNDO, AM1, and PM3, as well as ab initio, studies applying the STO-3G, 4-31G, 6-31G**, DZV, and DZP basis sets and also including the MP4 and QCISD(T) corrections were carried out on two tautomeric phosphorus hydrides H2PPH2 and HPPH3 and uni- and bimolecular reactions. First, the geometry of the two molecules was optimized using the theoretical methods mentioned in the Hartree-Fock (HF) scheme. The energies of the molecules at stationary points corresponding to HF/6-31G** geometries were subsequently calculated including electron correlation effects on the level of the fourth-order Moller-Plesset (MP4) perturbation theory or quadratic configuration interaction with single and double substitutions and triples contribution (QCISD(T)) calculated using the 6-311+G-(3df,2p) or 6-311++G(3df,3pd) basis set. Complete geometry optimizations at the MP4/6-31G** level resulted in only slight changes in the geometry and energy of the molecules as compared with HF results.