Effect of the Substituent and Hydrogen Bond on the Geometry and Electronic Properties of OH and O- Groups in para-Substituted Phenol and Phenolate Derivatives

Interrelations between intra- and intermolecular interactions were analyzed by using computational modeling of the para-X-substituted derivatives of phenol and phenolate (where X = NO, NO2, CHO, COMe. COOH. CONH2, Cl. F, H, Me, OMe, and CN) and their equilibrium H-bonded complexes with HB and B (where HB = HF and HCN and B- = F and CN). B3LYP/6-311++G** computation was applied. Both the substituent effect and H-bonding changed the electronic properties of the -O and -OH groups and geometric parameters of phenol and phenolate derivatives and their H-bonded complexes. C-O bond lengths and aromaticity indices of the ring were found to depend linearly on sigma(.-)(p) of the suhstiments. In the first case the greatest sensitivity on the subslituent effect was for 4-X-C6H4OH center dot center dot center dot CN- and 4-X-C6H4O center dot center dot center dot HF complexes, whereas for 4-X-C6H4O center dot center dot center dot HCN systems it was comparable with that for phenol derivatives and a little smaller than that for 4-X-C6H4O derivatives. This means that the strength of H-bonding may considerably change the sensitivity of the C-O bond length to the substiment effect. The greatest sensitivity of the aromaticity indices, both HOMA and NICS(1)zz, to a was found for phenolate and then for phenolate H-bonded complexes, followed by phenol complexes, and the lowest sensitivity was observed for phenol derivatives. The interatomic proton acceptor distance. heing a measure of the H-hond strength, was found to depend linearly on sigma(-)(p) of the substiments with a positive slope for O center dot center dot center dot HB (HF or HCN) interactions and a negative slope for OH center dot center dot center dot B (-) interactions. NBO charges on the oxygen and hydrogen atoms also depend on up of the substituents. In the latter case for strong H-hooded complexes (energy less than similar to -20 kcal/mol) the substiment effect works oppositely for 4-X-C6H4OH center dot center dot center dot B in comparison with the 4-X-C6H4O center dot center dot center dot HB systems, Moreover, following the Fspinoza et id. Chem. Phys. 2002, 117. 55291 and Grahowski et al, 1.1. Phys. Chem. B 2006.110. 6444 vertical bar classifications, the above and q(H) vs proton-acceptor distance relationships suggest a partially covalent character of the hydrogen bond for these complexes and the degree of its covalent nature depending on the substituent.