title: Comparison of conformer distributions in the crystalline state with conformational energies calculated by ab initio techniques.
abstract: The conformational preferences of 12 molecular substructures in the crystalline state have been determined and compared with those predicted for relevant model compounds by ab initio molecular orbital calculations. Least-squares regression shows that there is a statistically significant correlation between the crystal-structure conformer distributions and the calculated potential-energy differences, even though the calculations relate to a gas-phase environment. Torsion angles associated with high strain energy (> 1 kcal mol-1) appear to be very unusual in crystal structures and, in general, high-energy conformers are underrepresented in crystal structures compared with a gas-phase, room-temperature Boltzmann distribution. It is concluded that crystal packing effects rarely have a strong systematic effect on molecular conformations. Therefore, the conformational distribution of a molecular substructure in a series of related crystal structures is likely to be a good guide to the corresponding gas-phase potential energy surface.
authors.affiliation: Cambridge Crystallographic Data Centre, UK.
authors.forename: F H
authors.initials: FH
authors.lastname: Allen
authors.forename: S E
authors.initials: SE
authors.lastname: Harris
authors.forename: R
authors.initials: R
authors.lastname: Taylor
mesh_terms: D001555:Benzene Derivatives / Q000737:chemistry; D003461:Crystallography; D006838:Hydrocarbons / Q000737:chemistry; D015394:Molecular Structure; D013816:Thermodynamics
chemical_list: D001555:Benzene Derivatives; D006838:Hydrocarbons