ELECTRONIC SUBSTITUENT EFFECTS ON N-15 SHIELDINGS OF N-(ARYLMETHYLIDENE)CYCLOHEXANAMINE HYDROTRIFLUOROACETATES

An earlier 15N NMR study2 of several series of para-substituted N-(arylmethylidene)amines 1 and 2 has shown that the nitrogen shifts are sensitive to the electronic influence of the ring substituents (X), as reflected by the Hammett σsubstituent parameters. Reasonable linear correlations could also be obtained for the nitrogen shifts of compounds in each series and the β-carbon shieldings of 4-substituted ethenylbenzenes 3, with the changes in the 15N shifts generally being about twice that of the 13C shifts with respect to the substituent effects. To determine whether the greater sensitivity of the nitrogen shifts arises predominantly from a substituentinduced perturbation of the nitrogen unshared pair of electrons, we have measured 15N chemical shifts of a series of para-substituted N-(aryImethylidene)cyclohexanamine hydrotrifluoroacetates 4. © 1979, American Chemical Society. All rights reserved.