Spectra and structure of products from reaction of hydrogen chloride and lewis acids with sterically hindered phenols and phenoxyl radicals

Abstract

Earlier we studied sterically hindered phenols [i, 2], molecules with quinonoid structures (quinone [2], cyclohexadienone [i]), and their corresponding phenoxyl radicals [i, 2], which are stable on account of the bulky screening substituents, by the methods of vibrational spectroscopy. The effect of the unpaired electron on the optical parameters of the absorption bands in the vibrational spectra of the radicals compared with structurally similar molecules was investigated. In order to study the effect of change in the number of electrons in the anion--radical--cation series on the vibrational spectra we investigated the phenolate anion [3]. To complete the series of investigations it was necessary to study the vibrational spectra of the cation. It is known that cations can be formed either by the addition of a proton to a molecule or by the removal of a proton from a radical. Since it had earlier been established that N-aryl-l,4-benzoquinone imines are protonated at the nitrogen [4] while acetone [5], 2,6-dimethyl-4-pyrone [6], and N,N'-dicyclohexylacetamide salts [7] are protonated at the oxygen, it was interesting to check the capacity for protonation in the phenols (I) and (II).