Energetics and structural properties of neutral and deprotonated phenyl carbinols

Theoretical and experimental studies on the energetics, structure and other physicochemical properties of neutral 1-phenylethanol (1OH), diphenylmethanol (2OH) and triphenylmethanol (3OH) and their corresponding deprotonated anions (oxyanions, formed by deprotonation of the OH group) are reported in this work. The standard enthalpies of formation in the gas phase at T = 298.15 K, Hm0(g) have been determined. Quantum chemical calculations, at the DFT (particularly M05-2X method) and in some cases at the ab initio (G3) levels, have shed light on structural and electronic effects on the thermodynamic stability and intrinsic acidity of the studied compounds. These calculations confirmed the excellent consistency of the experimental results.Peer Reviewe

Energetic and Structural Properties of Two Phenolic Antioxidants: Tyrosol and Hydroxytyrosol

Theoretical and experimental studies on the energetic, structural and some other relevant physicochemical properties of the antioxidant tyrosol (1), hydroxytyrosol (1OH) molecules and the corresponding radicals 1 and 1O are reported in this work. The experimental values of the gas-phase enthalpy of formation, ΔH (g), in kJ·mol, of 1 (-302.4 ± 3.4) and 1OH (-486.3 ± 4.1) have been determined. Quantum chemical calculations, at DFT (M05-2X) and composite ab initio G3 and G4 levels of theory, provided results that served to (i) confirm the excellent consistency of the experimental measurements performed, (ii) establish that the stabilizing effect of H-bond of hydroxyethyl chain and aromatic ring (OH···π interaction) is smaller in radicals than in parent molecules, (iii) deduce - combining experimental data in isodesmic reactions - ΔH (g) of radicals 1 (-152.3 ± 4.4 kJ·mol) and 1O (-370.6 ± 3.8 kJ·mol), (iv) estimate a reliable O-H bond dissociation enthalpy, BDE of 1 (368.1 ± 5.6 kJ·mol) and of 1OH (333.7 ± 5.6 kJ·mol), and (v) corroborate - using >BDE criteria> - than 1OH is a more effective antioxidant than 1.Peer Reviewe