Understanding the kinetics and molecular mechanism of the Curtius rearrangement of 3-oxocyclobutane-1-carbonyl azide.

The approach presented here is an unprecedented insight into the understanding of kinetics and molecular mechanism of thermal Curtius rearrangement of 3-oxocyclobutane-1-carbonyl azide. Curtius rearrangement can proceed via concerted and stepwise mechanisms. The CBS-QB3 and CBS-APNO composite methods indicated that concerted pathway is dominant and 10 4 –10 5 times faster than stepwise path. The bonding evolution theory analysis at the B3LYP/6-311G(d, p ) revealed that the reaction via concerted pathway can be described with catastrophe sequence 9-CF † C † TS FC † FC † C-0 by the following chemical events: (a) change of topological signature of N 2 N 3 bond; (b) increasing the number of non-bonding monosynaptic attractor on N 1 atom; (c) breaking of N 1 N 2 bond and extrusion of nitrogen molecule; (d) decreasing the number of non-bonding monosynaptic attractors on N 1 atom; (e) breaking of C 4 C 5 bond and formation of pseudoradical centers on the C 4 and C 5 atoms; (f) annihilation of pseudoradical center on the C 5 atom; (g) change of topological signature of N 1 C 5 bond; and (h) formation of N 1 C 4 bond. Along the reaction course electron flow redistribution is asynchronous and bond breaking/forming do not takes place simultaneously demonstrating that the reaction is concerted yet highly asynchronous process. [ABSTRACT FROM AUTHOR]