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-fluorobenzylidenecyanoacetic acids are investigated by X-ray diffraction analysis with the aim of elucidating the factors responsible for the formation of crystal structures of cyanovinylbenzene derivatives. The crystal data for other known derivatives of this series are analyzed. It is revealed that, in the absence of strong hydrogen bonding, the main structure-forming function in crystals is fulfilled by intermolecular contacts of two types, namely, staking contacts of parallel and antiparallel molecules. The staking contacts of antiparallel molecules are most frequently realized. It is assumed that their presence in the structure determines the prevailing formation of centrosymmetric packings in the compounds under consideration.