“<Emphasis Type="Italic">ortho</Emphasis>-Effect” in thermal curtius rearrangement of alkylbenzoyl azides into isocyanates: A quantitative interpretation

The reasons for abnormally high reactivity of ortho-alkylbenzoyl azides in thermal Curtius rearrangement were established by the density functional method (PBE/TZ2P approximation). The key factor responsible for the rearrangement rate is the destabilization of the conjugated structure of arylacyl azide through steric effects of the ortho-substituents. Additional intramolecular hydrogen bonding, as in o-hydroxybenzoyl azide molecule, stabilizes the conjugated structure and increases the energy barrier to the reaction. Quantitative interpretation of the “ortho-effect” is given based on the dependence of the reactivity of ortho-alkylbenzoyl azides on the dihedral angle, which characterizes the extent of coplanarity of the acyl azide group and benzene ring. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 7–13, January, 2007.