Vicinal ¹³CH coupling through olefinic double bonds

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