Orientations of the hydroxyl and isopropyl groups in the cis and trans conformers of 2-isopropylphenol and 2-isopropyl-6-methylphenol

Abstract

Measurement of the long-range spin–spin coupling constants between methine or hydroxyl protons and the ring protons in 2-isopropylphenol shows that the trans conformer is favored by 2.5 ± 0.3 kJ/mol for a 2 mol% solution in CCl4, at 305 K. In this conformer the methine C—H bond of the isopropyl group points towards the hydroxyl group. In the cis conformer, the C—H bond points away from the hydroxyl group. In 2-isopropyl-6-methylphenol the conformation in which the O—H bond lies trans to the isopropyl group is preferred by 1.2 ± 0.3 kJ/mol in free energy at 305 K in CCl4 solution. This result agrees with an additive superposition of the conformational preferences of the hydroxyl groups in the monosubstituted phenol derivatives. Molecular orbital calculations do not agree with the existence of a cis conformer.