Intramolecular hydrogen bonds and antioxidant activity of aminophenols

We have used IR Fourier spectroscopy to study intramolecular interactions in solutions of aminophenols in n-hexane. When the hydroxyl group in the molecule is ortho to the amino group, O-H⋯N and N-H⋯O intramolecular hydrogen bonds are formed in the aminophenols. Adding two tert-butyl groups to the benzene ring of ortho-aminophenols strengthens the O-H⋯N bond in the molecules, and prevents formation of an N-H⋯O bond. Additional acylation of the amino group in ortho-aminophenols leads to formation of an O-H⋯O=C intramolecular hydrogen bond. Formation of the above-indicated intramolecular hydrogen bonds in aminophenols affects the course of radiation-induced reactions occurring in n-hexane with participation of these compounds. The antioxidant properties of the aminophenols are enhanced when the hydroxyl groups in the molecules are found in the free state, and are diminished when strong O-H⋯N or O-H⋯O=C intramolecular hydrogen bonds are formed. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 577–582, September–October, 2007.