A carbon-13 NMR study of 2-substituted-5-N,N-dimethylaminophenols: Correlations of substituent-induced chemical shifts with substituent parameters

The Carbon-13 NMR spectra of seven 2-subsituted-5-N,N-dimethylaminophenols and of the parent compound were recorded, and unequivocal assignments of the chemical shifts through the use of HETCOR and COLOC sequences were performed Large intramolecular interaction chemical shifts (ICS) were observed for C-1 (-10.2 to +8.1 ppm) and moderate values for C-2, C-3 and C-6 (-3.7 to +3.7), mostly for the oxygen-bearing derivatives [OCH3, NO2 and C(O)CH3]. Correlation analyses for the substituent-induced chemical shifts (SCS) with several sets of substituent parameters were carried out, through SSP, DSP and DSP-NER treatments, as well as through multiple regression analysis, The resonance contribution is predominant for C-1, C-5 and C-6, while for C-2 and C-3 the electronegativity parameter is the prevailing component, but for C-4 no correlation was found Negative rho(R) values for C-3 and C-6, and also negative rho(I) values for C-6 were observed (reverse substituent effect).