Carbon‐13, proton spin–spin coupling constants in some 2‐substituted propanes

Abstract Carbon‐13, proton coupling constants have been measured in eighteen different 2‐substituted propanes. 1J(C‐2,H) shows variations similar to those observed previously for monosubstituted methanes. 2J(C‐2,H) is essentially independent of the substituent at C‐2, while 2J(C‐1,H) varies over a range of at least 5 Hz. The latter coupling constant becomes more positive as the electronegativity of the substituent increases while 3J(CH) decreases as the electronegativity of the substituent increases. The observed trends in nJ(CH) are compared with those calculated using semi‐empirical molecular orbital theory at the INDO level of approximation.