Cooperativity in a cycloalkane‐1,2/1,3‐polyol corona: Topological hydrogen bonding in 1,2‐diol motifs.

A corona, consisting of 18 carbon atoms bearing 12 hydroxy groups in a continuous hydrogen‐bonded chain, is built up by alternating degenerate conformations of alternating alkane‐1,2‐diol and 1,3‐diol motifs. Geometries, proton nuclear magnetic resonance shifts and interaction energies for the dodecahydroxycyclo‐octadecane and selected fragments are determined by density functional calculations at the B3LYP/6‐311+G(d,p) level. Cooperative effects of O–H⋯O–H bonding are evident from the simple juxtaposition of these two motifs with a common OH group in butane‐1,2,4‐triol conformers. Bracketing a 1,2‐diol motif with two 1,3‐diol motifs in hexane‐1,3,4,6‐tetrol leads to a structure in which the 1,2‐diol motif displays a bond critical point for hydrogen bonding. This is associated with enhancement of the shift of the hydrogen‐bonded OH proton and of the corresponding H⋯O interaction energy. The full corona has a complete outer ring of O–H⋯O–H bond paths, and an inner ring of bond paths, due to C–H⋯H–C hydrogen–hydrogen bonding, which result in a central ring critical point. The topological O–H⋯O–H hydrogen bond, never seen in simple alkane‐1,2‐diols, is associated with cooperative enhancement of the H⋯O interaction energy, but this is not a necessary condition for a bond path: values for topological C–H⋯H–C hydrogen–hydrogen bonds can be as low as −0.4 kcal mol−1. [ABSTRACT FROM AUTHOR]