Unlocking a new hydrogen-bonding marker: C–O bond shortening in vicinal diols revealed by rotational spectroscopy.

The conformational space of cis-1,2-cyclohexanediol, a model molecule for cyclic vicinal diols, was investigated using rotational spectroscopy and density functional theory calculations. Four low energy conformers within an energy window of 5 kJ mol⁻¹ were identified computationally. A rotational spectrum of jet-cooled cis-1,2-cyclohexanediol was recorded with a chirped pulse Fourier transform microwave spectrometer. Two sets of rotational transitions were observed and could be assigned to conformers of cis-1,2-cyclohexanediol. The non-observation of other low energy conformers was explained by conformational conversion barrier height calculations and results from experimental spectra recorded with different carrier gases. Eight isotopologues, including those with ¹³C and ¹⁸O, of the lowest energy conformer were observed, allowing the determination of the semi-experimental equilibrium structure, r_e^SE. Interestingly, the structural analysis revealed that the C–O bond length of the intramolecular hydrogen-bond donor is shorter than that of the acceptor. This appears to be a general characteristic of vicinal diols and can be used as a novel hydrogen-bond marker in such compounds. [ABSTRACT FROM AUTHOR]