Theoretical Calculation of Substituent Effects on the O−H Bond Strength of Phenolic Antioxidants Related to Vitamin E

Abstract

Calculations on phenol and a large number of phenols substituted with methyl, methoxyl, and amino groups have yielded reliable gas-phase O−H bond dissociation energies, BDE(ArO−H)gas. Geometries for the phenol, ArOH, and aryloxyl radical, ArO, were optimized at the (semiempirical) AM1 level followed by single point density functional theory (DFT) calculations using a 6-31G basis set supplemented with p-functions on the hydrogen atom and the B3LYP density functional. This gave BDE(PhO−H)gas = 86.46 kcal/mol, which is in good agreement with the experimental value of 87.3 ± 1.5 kcal/mol. All but one of the compounds and conformations examined had weaker O−H BDE's than phenol, the exception being o-methoxyphenol with the O−H group pointing toward this substituent (BDE = 87.8 kcal/mol). Where comparison was possible, calculated differences in O−H BDE's were in excellent agreement with experiment (better than 1 kcal/mol). A simple group additivity scheme also gave excellent agreement with calculated BDE (ArO−H)gas values. Some potential new leads to phenolic antioxidants more active than vitamin E have been uncovered.

Determination of gas-phase acidities of dimethylphenols: Combined experimental and theoretical study

“…The same conclusion was also reached by Wright and coworkers [27]. In fact, several papers have reported the calculated gasphase structures of phenol as well as the structures of several monosubstituted phenols using different quality basis sets with success [28,29].…”

Synthesis, X-ray crystal structure and theoretical calculations of antileishmanial neolignan analogues

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Thermodynamic Properties of Quinoxaline-1,4-Dioxide Derivatives: A Combined Experimental and Computational Study

“…37 The B3LYP method comprises an exchange-correlation functional that mixes the nonlocal Fock exchange with the gradient-corrected form of Becke 38 and adds the correlation functional proposed by Lee et al 39 The use of the B3LYP method with a relatively large basis set is known to be an excellent computational choice. 18, [40][41][42][43][44] This approach was found to provide very good molecular geometries comparable to those obtained using more accurate and CCSD(T) or QCISD methods, which demand much greater computer resources, together with a medium-sized basis set. 41,42 Therefore, use of an extended basis set is needed; unfortunately, this makes infeasible the application of these accurate methods to the majority of chemical compounds in which the chemists are interested, i.e., large-sized molecules and compounds containing heavy atoms.…”