Acta Crystallographica Section B

Structural Science

Volume 57, Part 6 (December 2001)

research papers

Acta Cryst. (2001). B57, 815-827 [ doi:10.1107/S010876810101360X ]

Rules governing the crystal packing of mono- and dialcohols

R. Taylor and C. F. Macrae

Abstract: A new program, Mercury, has been used to survey 144 monoalcohol (C_mH_nOH) and 101 dialcohol [C_mH_n(OH)₂] crystal structures. Results show that their hydrogen-bonding patterns are strongly correlated with steric effects. Primary monoalcohols have a strong preference to form infinite OHOH chains. Secondary monoalcohols form chains and rings of hydrogen bonds with about equal facility. Tertiary monoalcohols very often form isolated OHO hydrogen bonds or structures containing no OHO hydrogen bonds at all. In the latter case, however, the structures almost invariably contain CHO and/or OH [pi] interactions. Substitution on the [beta] -carbon(s) of monoalcohols has a profound effect on packing patterns, with increased substitution disfavouring chains and rings. Dialcohols show a much stronger preference for chains of hydrogen bonds, compared with monoalcohols. This is particularly so when at least one of the hydroxyl groups is primary, in which case chains are overwhelmingly preferred. Once again, substitution on the [beta] -C atoms is influential, heavy substitution tending to lead to packing arrangements that involve isolated or intramolecular OHO hydrogen bonds. Dialcohols almost never crystallize without at least some OHO hydrogen-bond formation. In both monoalcohols and dialcohols, chains show a stronger preference to be helical (usually threefold helices) as steric hindrance increases. Hydrogen-bonded rings usually contain four OHO hydrogen bonds. It is possible that empirical observations such as these may aid crystal-structure prediction.

Keywords: Mono- and dialcohols; crystal packing; hydrogen-bonding patterns.