The electronic structure and reactivity of small ring compounds—VII : The CMR spectra of 1-cyanobicyclo[1.1.0]butane

Abstract

The 25·2 MHz CMR (FFT) spectra of 1-cyanobicyclo [1.1.0]butane are reported both with and without hydrogen decoupling. Chemical shifts are discussed in terms of dipolar resonance contributions to the ground state and the unsaturated nature of the bicyclobutane ring. The C-H coupling constants, including directly bonded and long range interactions, are reported. It is suggested that the large long range H x′-C 2 coupling constant is a result of a favorable interaction between the H x′-C 4 bond and C 2 bond and C 2 and that the H 3-cyano carbon coupling constant results from a 0° dihedral angle and to a small extent, if at all, from a favorable geometry. The C 1-C 2 (22 Hz) and C 1-C 3 (16 Hz) 13C- 13C coupling constants are presented, compared with the calculated values, and discussed in terms of hybridization. The possibility of a negative value for the C 1-C 3 coupling constant is also considered. It is pointed out that using coupling constant-hybridization relationships and extrapolating from several known to an unknown hybridization around a carbon atom can, in many cases, lead to a sizeable error in calculated hybridization.