Alkali Salts of Nitranilic and Cyanochloranilic Acids

Abstract

Series of novel alkali salts of nitranilic acid (3,6-dinitro-2,5-dihydroxyquinone) and cyanochloranilic acid (3-cyano-6-chloro-2,5-dihydroxyquinone), and also of neutral cyanochloranilic acid dihydrate, were prepared and their structures were studied. The nitranilate dianion revealed a considerable conformational flexibility of nitro groups. Steric and inductive effects exerted by different substituents (nitro, cyano and chloro) and their influence on molecular geometry and crystal packing are discussed.

An unusual intermolecular interaction between a lone pair and an electron-rich π-electron system of a quinoid dianion

“…Bond lengths in the DHQ dianion (Table S3) are in good agreement with its other alkali salts, confirming the structure shown in Scheme . Several substituted 2,5-dihydroxyquinones also have two delocalized π-systems separated by two single C–C bonds: the 3,6-dichloro analogue (chloranilate dianion, CA ), ,− the 3,6-dibromo analogue (bromanilate dianion, BA ), the 3,6-dinitro analogue (nitranilate dianion, NA ), , and the 3-cyano-6-chloro analogue …”

“…Experimentally determined charge densities for chloranilate and nitranilate dianions can be compared to those of DHQ to quantify substituent inductive effects. Electron-withdrawing substituents enhance negative charge delocalization and thus increase hydroxyl group acidity. , Their effect on the molecular geometry is negligible. Bond orders calculated from electron density show a clear trend (Table ): electron density in the carbon ring is reduced as the electron-withdrawing power of the substituents increases.…”

“…Several substituted 2,5dihydroxyquinones also have two delocalized π-systems separated by two single C−C bonds: the 3,6-dichloro analogue (chloranilate dianion, CA), 18,24−26 the 3,6-dibromo analogue (bromanilate dianion, BA), 27 the 3,6-dinitro analogue (nitranilate dianion, NA), 28,29 and the 3-cyano-6-chloro analogue. 30 Experimentally determined charge densities for chloranilate 18 and nitranilate dianions 28 can be compared to those of DHQ to quantify substituent inductive effects. Electronwithdrawing substituents enhance negative charge delocalization and thus increase hydroxyl group acidity.…”

“…Electron-withdrawing substituents enhance negative charge delocalisation and thus increase hydroxyl group acidity. 24,30 Their effect on molecular geometry is negligible. Bond orders calculated from electron density show a clear trend (Table 1): electron density in the carbon ring is reduced as electron-withdrawing power of the substituents increases.…”