Determination of substituent effects by factor analysis and multiple linear regression for the carbon-13 nuclear magnetic resonance chemical shifts in 4-substituted phenols and 2-nitrophenols

Carbon-13 nuclear magnetic resonance chemical shifts are reported for a series of 4-substituted phenols and 2-nitrophenols in dimethyl sulfoxide solution. For chemical shift correlations, it was found by factor analysis and iterative multiple linear regression that the para chemical shifts require two substituent factors whereas the ipso, ortho, and meta chemical shifts require three factors. Regression analyses were performed using the field and resonance parameters (σF, σR0) and the appropriate ipso, ortho, and meta parameters (I, O, M) determined by Reynolds. Good correlations were obtained except for the three meta carbon analyses, where the correlation coefficients range from 0.877 to 0.963.