M. Horwath, V. Benin
Feb 15, 2008
Citations
0
Influential Citations
6
Citations
Journal
Journal of Molecular Structure-theochem
Abstract
Abstract The current report presents the first theoretical study of the restricted C N bond rotation in carbamoyl chlorides. Several N -benzyl- N -methylcarbamoyl chlorides were investigated, with varying pattern of substitution in the aromatic ring. Optimizations and frequency calculations were conducted employing DFT at the B3LYP/6-31+G(d) level of theory. Each of the studied structures exhibits a pair of rotamers (s- Z and s- E ), generated upon rotation around the C( O) N bond. The s- E isomer is the global minimum in every case, but the preference for it is usually less than 1 kcal/mol. Two possible transition state structures were identified for the rotamer interconversion: TS syn and TS anti , in close analogy to other related compounds, such as amides and carbamates. In contrast to the two latter types, however, the preferred transition state in the case of carbamoyl chlorides is TS syn , which we attribute to a stabilizing gauche effect. The optimized minima structures of the studied carbamoyl chlorides were subjected to GIAO B3LYP/6-311+G(2d,p) calculations, and the resultant isotropic shifts were found to be in excellent agreement with available experimental values. This has allowed us to provide unambiguous NMR signal assignments for the s- E and s- Z isomers of the studied compounds.