Detailed statistical analyses of magnetic anisotropy and electric field effects on proton chemical shifts

Abstract

The effect of substituents on proton chemical shifts has been analysed in terms of magnetic anisotropy and electrical field effect contributions and reasons are given for the necessity for detailed statistical analyses. By using data in the literature statistical information is given by which the success of such analyses can be judged for the effect of the carbonyl, the ethylenedioxy, the ethylenedithio and the cyano group, and the CH, CC, and CC bond. Frequently the inter-correlation coefficients of pairs of the explanatory variables used are large and the data are not statistically suitable for producing reliable values of magnetic anisotropy and electric-field effect constants. The magnetic anisotropy of the CH bond(s) replaced by the substituent is insignificant in these analyses. The electric-field effect is greater for measurements in deuteriochloroform than for measurements in carbon tetrachloride or cyclohexane.