Correlations between35Cl Nuclear Quadrupole Resonance (NQR) Frequencies of Chlorobenzene Derivatives and Characteristic Reaction Parameters of the Substituents

摘要

The35Cl NQR frequencies (at 77deg;K) of a number of chlorobenzene derivatives have been measured. The frequencies (including additional data from the literature) have been correlated with characteristic parameters, such as Taft'ssgr;Iandsgr;R. It is found that the Brayndash;Barnes relation can be somewhat improved by introducing a parameterkgr;:ngr;thinsp;equals;thinsp;ngr;0thinsp;plus;thinsp;ikgr;inodot;.The following relations are found: (a) the effects of more than one substituent on the benzene are additive; (b) steric effects (ohyphen;substituents) are not important for the NQR frequencies; (c) a correlation between the NQR frequencyngr;and Taft'ssgr;Iandsgr;R(correlation coefficientrthinsp;equals;thinsp;0.976) shows the importance of the inductive effect on NQR. The mesomeric effect plays only a minor role in35Cl NQR in benzene derivatives. Unknownsgr;Ivalues may be gained from NQR measurements; for the evaluation ofsgr;R, the determination of the chemical shift of19F NMR seems to be the better method.