Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

Principal component analysis technique has been applied to analyse the substituent effect on carbonyl stretching frequency and ¹³C NMR chemical shifts. The general formula for the investigated molecules is X-G-Y, where X represents the set of substituent (OMe, Me, F, Cl, Br, CN and NO₂), Y is the probe site and G is benzene ring. According to the indicator function two significant components are responsible for the substituent effect. The validity of several substituent parameters have been investigated by target testing technique. Invariabily substituent parameters derived by iterative multiple linear regression analysis viz. σ_R (Reynolds), σ_F (Reynolds) and σ_R (NMR) have lower SPOIL values when compared with other substituent parameters. Model designing f IR and ¹³C NMR data matrices separately have shown that models which incorporate σ_R (Reynolds) and σ_F (Reynolds) or σ_R (NMR) and a substituent field parameters have the lowest root mean square error RMSE. Substituent effect on several properties are better correlated with Reynolds' σ_R and σ_F than with other commonly used substituent parameter(s). The orthogonality of substituent parameters used in the model can be achieved by including the methyl group in the substituent set.