The chlorotropic isomerization mechanism for amidinium tetrachlorophosphorates

MNDO-PM3 quantum-chemical calculations have been combined with³⁵Cl NQR spectroscopy in research on the thermodynamic and kinetic stability of chlorotropic isomers in the Cl₄P(NCH₃)₂CR amidinium tetrachlorophosphorate series, in which R=C₆H₅, CCl₃, CF₃, Cl; the relative thermodynamic stability of the phosphorate P^VI isomer is higher than that of the phosphetidine P^V one and has a minimum in the series for the CF₃ derivative. The chlorotropic P→C transformation of the isomeric forms of the amidinium tetrachlorophosphorates occurs in liquid solutions and in melts by an intramolecular sigmatropic mechanism, not by the formation of a contact ion pair. Institute of Bioorganic Chemistry and Petroleum Chemistry, National Academy of Sciences of Ukraine, 1 Murmanskaya ul., Kiev 253094, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 3, pp. 155–161, May–June, 1999.