A theoretical comparison of phosphino and amino groups in the isocyanide–cyanide rearrangement

Abstract

Ab initio molecular orbital calculations have been used to study the isocyanide–cyanide rearrangement involving the migration of the hydrogen, amino and phosphino groups. Geometries were optimized using MP2/6-311 G(d,p) while relative energies were obtained from CISDQ/6-311 ++ G(d,p) wavefunctions. Structures and some spectroscopic properties of the equilibrium structures are predicted. Phosphinoisocyanide is found to lie 16 ± 2 kcal mol^–1 above phosphinocyanide, and to rearrange to the latter with an energy barrier of 27 ± 2 kcal mol^–1. Energetics (kcal mol^–1) of two other rearrangements are as follows: isocyanamide (0)→ TS (37)→ cyanamide (–44) and hydrogen isocyanide (0)→ TS (30)→ hydrogen cyanide (–14). Phosphinoisocyanide exhibits kinetic and thermodynamic stability similar to hydrogen isocyanide (relative to their isomers) and should thus be detectable in both gaseous and condensed phases.