A theoretical study of the structure, electronic properties, and reactivity of phenylcyanates

Abstract

Calculations are reported on the structure and electronic properties of phenylcyanate and its 4-nitro and 4-amino derivatives using both the semi-empirical AM1 and PM3 methods and the ab initio 6–31G ∗∗ basis set. The calculated structures are compared with crystallographic data where available and their electronic properties with their expected reactivity. A study of the reactions of the phenylcyanates with methoxide ion in methanol using the AM1/COSMO method suggests that the rate-controlling step of the nucleophilic substitution reactions of the phenylcyanates is controlled by the addition of methoxide ion to the cyanato group to give a stable intermediate. Ring substituents exert little effect on this process, although, thermodynamically, the formation of the 4-nitrophenylcyanate intermediate is favoured over the others. The conversion of the intermediate into products is strongly affected by the nature of the ring substituents so that both the kinetics and thermodynamics of the subsequent displacement of the phenoxide ion is facilitated by the nitro group and retarded by the amino group.