Synthesis and Spectral Characteristics of Substituted 2,6-Dibenzylidene Cyclohexanone

Abstract

The design and synthesis of substituted 2,6-Dibenzylidene cyclohexanone based bischalcone derivatives were studied in this research through one of the most important Claisen-Schmidt condensation reaction of donor-acceptor conjugated system and their spectral properties has been studied. A number of substituted 2,6-Dibenzylidene cyclohexanone was synthesized through the reaction of commercially available para substituted benzaldehyde and cyclohexanone in presence of basic NaOH, where NaOH acts as a catalyst. The structures of the synthesized products were characterized by their physical, chemical and UV, IR & 1H NMR spectra. The compounds were soluble in most organic solvents. 2,6-Bis-(4-dimethyl-amino benzylidene)-cyclohexanone showed acidochromic behavior with the change of pH. This compound when interacts with acids changed the color of compounds due to the presence of chromophore. 2,6-Dibenzylidenecyclohexanone 1 absorbed at 330 nm and 2,6-Bis-(4-dimethylamino-benzylidene)- cyclohexanone 5 disclosed high absorption at 452 nm. The bathochromic shifts for compound 5 is due to the presence of electron donating N(CH3)2 substituents and the hypsochromic shifts for compound 1 is mainly due to the basic chalcone framework where no substituent is present. Also 2,6-Bis-(4-methoxy-benzylidene)-cyclohexanone 4 showed absorption at 359 nm (bathochromic shifts, lesser than compound 5) due to the presence of electron donating MeO substituents. Probably the halogen substituent contributed very little effect to the absorption and hence 2,6-Bis-(4-chloro-benzylidene)-cyclohexanone 2 exhibited absorption at 333 nm. Further 2,6-Bis-(4-nitro-benzylidene)-cyclohexanone 3 showed absorption at 340 nm. The solvatochromic behavior study of these compounds revealed that when these compounds were dissolved in different solvents (Ethanol, Ethyl acetate and Dichloromethane) formed hydrogen bonds on the basis of the polarity of the solvent and stabilized the product. EtOH is a polar protic solvent and the polarity of etanol is more than ethyl acetate and dichloromethane hence in case of compounds 1,4 & 5 exposed greater max (bathochromic shifts) in EtOH due to the formation of hydrogen bonds. This shifts turned to hypsochromic from ethyl acetate to DCM as these are aprotic. This could be due to the decrease in energy of the excited state as a function of increase in solvent polarity, which is in the order: DCM < Ethyl acetate < EtOH and stabilized the compound.