How OH and O- groups affect electronic structure of meta-substituted and para-substituted phenols and phenolates

An application of two independent quantum chemistry-based concepts, a substituent effect stabilization energy (SESE) and a charge of the substituent active region (cSAR), for describing substituent effects allows to investigate a nature of mutual interactions between substituents. The B3LYP/6-311++G(d,p) method is employed to examine changes in properties of a reaction center Y (Y = OH or O- groups) and a transmitting moiety (the benzene ring) due to substituent effects in a series of meta-X-substituted and para-X-substituted phenol and phenolate derivatives (X = NMe2, NH2, OH, OMe, CH3, H, F, Cl, CF3, CN, CHO, COCl, COMe, CONH2, COOH, NO2, NO). HOMA, NICS(1) and pEDA parameters are used to characterize pi-electron delocalization of the transmitting moiety. Relations between cSAR(X) and sigma constants show almost identical sensitivity of the substituent effect in meta-substituted phenol and phenolate derivatives, whereas in para-substituted analogs, different kinds of intramolecular interactions have been revealed. Due to electron attractive property of OH group in meta position, dependences of cSAR(X) on SESE show a dramatically different picture of interaction in meta-substituted phenols as compared to that found for all other series studied. Moreover, this group affects in a different way the electron-attracting and electron-donating substituents in meta position. A clear substituent effect on pi-electron delocalization of the benzene ring is observed only in para-substituted phenolate derivatives. The application of cSAR(X) parameter allows to estimate a difference between its value for a particular substituent in meta and para derivatives. In some cases, this difference amounts up to similar to 53% of the range of cSAR(X) variability.