Collect. Czech. Chem. Commun. 1991, 56, 2188-2198

Three-dimensional structures of substituted benzylphenyl ethers

Bohdan Schneidera, Karel Humlb and Václav Rejholeca

a Research Institute for Pharmacy and Biochemistry, 130 60 Prague 3
b Institute of Macromolecular Chemistry, Czechoslovak Academy of Sciences, 162 06 Prague 6


Forty nine three-dimensional crystal structures of a benzylphenyl ether fragment retrieved from the Cambridge Structural Database were confronted with computed conformational maps of the fragment. Due to the symmetry the number of analyzed fragments rose to 98. When an endocyclic torsion angle of a phenyl ring deviates from 0° the adjacent torsion angle is deformed in opposite direction compensating thus the deviation from planarity. The shape of the fragment is mainly controlled by torsion angles τ1 = C-C-O-CH2, τ2 = C-O-CH2-C, and τ3 = O-CH2-C-C. The attachment of both phenyl rings to the -CH2-O- moiety is not symmetrical and the deformation depends on the value of the τ3 angle. In the crystal, the fragment prefers conformation with τ1 around 0°, τ2 around 180° and with broad bimodal distribution of τ3 around 0° and ±90° despite the fact that energetically equivalent regions exist in the potential energy maps for τ2 values near 60° and 300° and that many crystal structures with τ3 around 0° lie in higher energetical regions than those with τ3 around 90°. Thus a significant difference between the crystal and simulated gas phase conformations was observed supporting the hypothesis that crystals prefer flatter and more storable molecular conformations.