The allyl and benzyl groups as hydrogen bond acceptors in derivatives of 2-allylphenol and 2-benzylphenol

Abstract

The ¹H nmr spectra of 2-allylphenol, 2-allyl-6-methylphenol, 2-allyl-6-chlorophenol, and 2-benzyl-4-chlorophenol are analyzed in some detail. It is shown that, relative to a methyl group, the allyl and benzyl moieties, respectively, favor a cis orientation by 1570 ± 250 J/mol and 900 ± 220 J/mol in free energy at 305 K in CCl₄ solution. These numbers appear to be independent of the CCl₄ solvent. Coupling parameters within the allyl group in these molecules and in propene and allylbenzene show some regularities but are probably not reliable indicators of the allyl conformational preference, at least in the absence of a model allowing for hindered rotor state populations.