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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.