NMR study of coupling effects

Abstract

1. Study has been made of the13C NMR spectra of certain 1-alkoxy-2-chloroethenes and 1-alitoxy- and 1-alkylthio-2,2-dichloroethenes. On the basis of an analysis of the magnitude and character of the chemical shifts of the carbon atoms of the vinyl fragment, and the results of calculations on the potential energy for internal rotation, it was concluded that an increase in the size of the alkyl substituent eventually leads to breakdown of the p-π coplanarity in the 1-alkoxy-2-chloroethenes. The cis isomers of these compounds, and the 1-alkoxy-2,2-dichloroethenes, exist in gauche conformations. The s-trans conformation is most probable for the 1-alkylthio-2,2-dichloroethenes, regardless of the size of the alkyl substituent. 2. The difference in chemical shifts of the double-bond carbons parallels the known relative activities of the gem-dichlorovinyl ethers and sulfides, and their unsaturated analogs, in reactions with electrophilic compounds.