Conformational analysis of diols: Role of the linker on the relative orientation of hydroxyl groups

Abstract

Conformational flexibility of three covalently linked alcohol dimers, composed of xanthenol units and diphenyl ether (DPE(OH)2), 9,9‐dimethylxanthene (XAN(OH)2), or biphenyl (BP(OH)2) linkers was studied. The relative orientation of the two alcohol units (In‐In, In‐Out, and Out‐Out conformers) in the model compounds was investigated using NMR spectroscopy, X‐ray crystallography, and density functional theory (DFT) calculations. Diols containing rigid linkers, such as XAN(OH)2 and BP(OH)2, favor the formation of an In‐In conformer in solution, and the interconversion between different conformers was slow on the NMR timescale. Interestingly, XAN(OH)2 adopted an In‐Out conformation in the crystalline solid state, possibly due to additional intermolecular interactions. More flexible DPE(OH)2 was found to freely interconvert on the NMR timescale. This study provides important structural information that can be utilized in catalysis, metal‐ligation, and other applications.