Cooperative Hydrogen-bonding Network Research Articles

Hydrogen bonding in crystalline mestranol methanolate

The crystal structure of the synthetic sex steroid mestranol is determined for a crystal grown from methanol. One methanol molecule per steroid molecule is incorporated in the crystal lattice and facilitates formation of a favourable cooperative hydrogen bond network. Close contacts are formed between methanol molecules, in which the hydroxyl O-atoms approach the methyl carbon atoms to 3.15 Å in the so-called umbrella configuration. In the latter, the intermolecular interaction energy is close to zero.

Weak hydrogen bonding. Part 2. The hydrogen bonding nature of short C–H ⋯π contacts: crystallographic, spectroscopic and quantum mechanical studies of some terminal alkynes

In a number of crystalline terminal alkynes, the alkyne C–H groups form short intermolecular contacts with other alkyne or with aromatic moieties. A particularly short C–H ··· phenyl contact is found in (±)-3-phenylbut-1-yn-3-ol, with an H ··· midpoint separation of only 2.51 A. Crystallographic, spectroscopic and computational evidence is given to show that these contacts represent hydrogen-bond-type interactions. Quantum chemical calculations indicate hydrogen bond energies in the range 1–2.2 kcal mol–1. Interconnected contacts such as CC–H ··· CC–H ··· CC–H exhibit a pronounced cooperativity effect, with energy increases of ∼0.5 kcal mol–1 compared with isolated contacts. Based on these results, the role of the terminal alkyne group in cooperative hydrogen bond networks is described as topologically paralleling that of hydroxy groups.