Factor Analysis of Long Range Substituent Effects on C-13 NMR Chemical Shifts and Target Factor Testing of Different Types of Substituent Parameters

Abstract

AbstractA factor analysis technique has been used to analyse 186 long range C-13 substituent chemical shift (scs) of 90 compounds of the general formula X - G - Y ; X represents the set of substituents, G is a hydrocarbon skeleton, in some cases unsaturated (phenylene) and in other cases saturated. Y consists of a variety of groups which contain the probe site. The data were taken from the literature. Although they were measured in different laboratories, the solvent was CDCl3 in every case. From the value of the factor indicator function (IND) it was concluded that two factors were significant. The validity of several empirical and theoretical substituent parameters has been investigated by Target testing. Models were constructed for the substituent effect. Results from Target factor testing, model designing and linear regression analysis have shown that Reynolds’ σOR and σF are the best substituent parameters in reproducing the C-13 substituent chemical shift.