Study of substituent effects in substituted dibenzal acetones

Krishna Engineering College, Chennai-600 134, India

Department of Chemistry, P.S.G.R. Krishnammal College for Women, Peelamedu, Coimbatore-641 004, Tamilnadu, india

E-mail : chem_renu@yahoo.co.in

Manuscript received 4 July 2005, accepted 16 October 2006

The present work involves a detailed study of the ultra-violet absorption spectra of various substituted dibenzylidene ketones derived from acetone, ethyl methyl ketone, diethyl ketone, cyclopentanone and cyclohexanone by condensing with several meta- and para-substituted benzaldehydes in \(n\)-hexane and in ethanol to ascertain the transition dominant in these solvents. These ketones exist as equilibrium mixtures of s-cis, cis and s-cis, trans conformations. The ultraviolet absorption spectra of the ketones exhibit two bands due to π*← π transition around 250 and 320 nm. The 320 nm band is prominent in all the cases. There is no indication of π* ← π transition in any of the spectra. The 320 nm band is structureless in all the cases except those shown by the dibenzylidene ketones derived from cyclopentanone in hexane. Therefore it can be inferred that the dibenzylide ketones derived from all the ketones except those derived from cyclopentanone are non-planar.