Geminal C,H spin coupling in substituted alkenes

Two-bond C,H coupling constants for the coupling pathways C_?C? H_ (type I) and (type II) have been studied in a variety of mono-, di- and trisubstituted ethylenes. For ²J(CH) of type I, additive increments have been determined for 20 substituents, which allow a satisfactory calculation of coupling constants, including relative signs, in di? and trisubstituted ethylenes. Several applications for E/Z isomers are presented. In cyclic compounds a positive coupling increment, δJ, is observed in going from 6? to 5?membered ring compounds.