Formation of crystal structure of cyanovinylbenzene derivatives: X-ray structure investigation of ethyl esters of 3,4-dimethoxy-, 3,4,5-trimethoxy-, and 4-fluorobenzylidenecyanoacetic acids

Ethyl esters of 3,4-dimethoxy-, 3,4,5-trimethoxy- and 4-fluorobenzylidenecy anoacetic acids are investigated by X-ray diffraction analysis with the aim of elucidating the factors responsible for the formation of crystal struct ures of cyanovinylbenzene derivatives. The crystal data for other known der ivatives of this series are analyzed. It is revealed that, in the absence o f strong hydrogen bonding, the main structure-forming function in crystals is fulfilled by intermolecular contacts of two types, namely, staking conta cts of parallel and antiparallel molecules. The staking contacts of antipar allel molecules are most frequently realized. It is assumed that their pres ence in the structure determines the prevailing formation of centrosymmetri c Packings in the compounds under consideration (C) 2001 MAIK "Nauka/lnterp eriodica".