| Abstract: | The proton NMR spectra of four cis/trans pairs of 1,2-disubstituted olefins have been analysed. The observed trends of the olefinic, vicinal and allylic proton-proton coupling constants are discussed in terms of rehybridization at the sp2 carbon atoms. It is found that in these substances the trans-allylic couplings are generally more negative than the cis-allylic couplings contrary to Barfield's1 theoretical prediction but in agreement with some earlier experimental data. Steric hindrance between cisoid substituents is cited as the probable origin of this end related trends. |
