INTERACTIONS IN MOLECULAR-CRYSTALS, 143 - ORTHO-BENZENE DERIVATIVES WITH MESHED COGWHEEL CHLOROMETHYL AND METHYLAMINO SUBSTITUENTS - STRUCTURES AND ROTATION ENTHALPY HYPERSURFACES

Facets of molecular dynamics in organic compounds such as coupled rota tions of adjacent substituents are advantageously discussed based on s tructural data. Within this context, crystal structures of spatially o vercrowded ortho-disubstituted benzene derivatives with chloromethyl o r methylamino groups are presented together with semiempirical enthalp y hypersurfaces for the substituent rotation. Both compounds, 1-trichl oromethyl-2-dichloromethyl-benzene as well as 1-trimethylammonium-2-di methylamino-benzene exhibit comparable steric overcrowding and their p referred dynamics are predicted to be dominated by the rotation of the threefold substituted group during an approximate standstill of the t wofold substituted, mirror-symmetric one. According to known solid sta te NMR measurements as well as to atom/atom-potential model calculatio ns for the pentachloro ortho-xylene derivative, this molecular dynamic mode is still active in the crystal.