Vicinal 13CH coupling through olefinic double bonds

Values of long range ¹³CH coupling through the double bond in a number of isopropenyl compounds are reported. There is evidence that substituent dependence of ³J(CH) is not related linearly to that of H? H couplings in vinyl compounds. The ratio of ³J(CH) to ³J(HH) in analogous pairs of compounds appears to increase with decreasing substituent polarity and increasing steric bulk.