Halogenotropy in the CNC Triad of Trihalomethyl Isocyanates and Conformational Lability of Their Iminocarbonyl Isomers

According to the MNDO calculations, halotropic transformation of trihalomethyl isocyanates X₃CNCO (X = F, Cl, Br) follows sigmatropic mechanism with formation of a contact ion pair. In keeping with the experimental data, the isocyanate structure of the fluorine derivative and carbamoyl structure of the chlorine and bromine analogs are determined by the relative stabilities of isomeric forms. Specific solvation gives rise to a weak tendency to reduction of the activation energy of chlorotropy and leveling of the stability of chlorotropic isomers.