Proton-driven conformational change in a 2-aryl-p-carborane constrained by an intramolecular C–H⋯O hydrogen bond

2-(2-Hydroxyphenyl)-p-carborane forms an intramolecular hydrogen bonding based on the results of X-ray, IR, and 1H NMR studies. The hydrogen bonding is released by the addition of acid in solution. Density functional theory (DFT) calculations on the phenol, phenolate and protonated phenol structures indicated two stable conformational state, hydrogen bonding form for phenol and phenolate, and dihydrogen bonding form for protonated phenol.