DFT investigation on hydrogen bonding in cyclohexane-1,2,3,4,5-pentol crystal structure

The cyclohexane-1,2,3,4,5-pentol,C6H12O5 is a natural product extracted from Adiscanthus fusciflorus (Rutaceae). It crystallizes in the non-centrosymmetric space group P21 with one molecule in the asymmetric unit and it has been postulated to have at least ten strong O-H…O intermolecular interactions, two per each OH group of one molecule, producing a three-dimensional network. The crystal packing is defined by O-H…O hydrogen bonds. Due to the crucial role of the hydrogen bonds in defining the crystal structure, theoretical investigations in the gas phase have been carried out in order to explore the hydrogenbonding mechanism through a quantitative Kohn-Sham molecular orbital and corresponding energy decomposition analyses. The existence of a covalent component in hydrogen bonds has been proved which originates from donor-acceptor orbital interactions in the σ-electron system. Our analyses show that the stability of the crystal structure is enhanced by the formation of two hydrogen bonds with two vicinal molecules for each OH group in C6H12O5 molecule with respect to the formation of one or two hydrogen bonds with only one vicinal molecule, thus confirming the proposed existence of ten strong O-H…O intermolecular interactions for each molecule in the asymmetric unit. The presence of a cooperativity effect is observed which originates from a charge separation induced by the two vicinal molecules hydrogenbonded to an OH group in C6H12O5 molecule.