ONE-BOND CC SPIN-SPIN COUPLING-CONSTANTS IN DERIVATIVES OF BENZENE - NONLINEARITY OF (1)J(CC) VS SUBSTITUENT ELECTRONEGATIVITY

A set of one-bond CC coupling constants has been determined for mono- and disubstituted benzenes. Large 1J(CC) values have been found within the benzene rings bearing highly electronegative substituents such as halogens, methoxy and nitro groups and small values for those with el ectropositive substituents. The total range of 1J(CC) couplings observ ed in our work is larger than 50 Hz. These large variations of CC spin -spin couplings are interpreted in terms of Fermi-contact contribution s and the redistribution of s-electrons within a CC bond under influen ce of substituents. Contrary to some previous findings the data obtain ed in the present work indicate that the relationship between 1J(CC) a nd the substituent electronegativity is not linear.