Principal component analysis in studies of substituent-induced chemical shifts of 1,4-disubstituted benzenes

Chemometric analyses of 1,4-disubstituted benzene aromatic carbon atom NMR chemical shifts, bearing 14 substituents (X) within a complete series invol ving the same substituents as fixed groups (Y), are reported. The substitue nt effects of (i) strong electron donors (NMe2, NH2 and OMe), (ii) halogens (F, Cl and Sr), (iii) electron accepters (CFB, CN and NO2), (iv) accepters of the carbonyl type [C(O)OEt, C(O)Me and CHO] and (v) neutral groups (H a nd Me) were studied using principal component analysis (PCA). The charge al terations (Deltaq) induced by introducing a substituent X at C-l were also analyzed by the means of PCA of data obtained from theoretical calculations (AM1 method). The correlations among the substituent chemical shifts (SCS) and among the charge alterations (Deltaq) and the dependence of SCS on cha rge alterations were analyzed by regression analyses applied to the scores of the first principal components (PC1) obtained in the PCA of the SCS and Deltaq values. Copyright (C) 2001 John Wiley & Sons, Ltd.