Allylic Proton-Proton Coupling in Stereodefined Alkylidenecyclobutanes and Alkylidenecycopentanes

analysis of the 1h nmr spectra of eight stereodefined alkylidenecycloalkanes allows determination of the magnitude of allylic coupling in these compounds. in contrast to the trend normally observed, the magnitude of transoid-allylic coupling was found to be invariably greater by ~0.5 hz than the cisoid-allylic coupling. the larger transoid-allylic coupling may be attributed to the slightly smaller dihedral angle relating allylic =c-c-h plane with the c=c-c plane in the e-isomers.