Calculation of the relative basicity of three α,ω‐diphenylpolyenes with trifluoroacetic acid

Abstract

Linear polyenes are an important class of compounds containing two or more alternating carbon-carbon double and single bonds that are soluble primarily in organic non-polar solvents. However, determining the relative basicity of unsubstituted polyenes experimentally has proven to be challenging in practice because such studies require mixing non-polar polyene-organic solvent mixtures with high concentrations of moderately polar organic acids. In this study, we used both computational and experimental approaches to calculate potential sites of protonation of trans-1,4-diphenyl-1,3-butadiene (DPB), all trans-1,-6-diphenyl-1,3,5-hexatriene (DPH), and all trans-1,8-diphenyl-1,3,5,7-octatetraene (DPO) with trifluoroacetic acid (TFAH) in both n-hexane or benzene solvents. Density functional theory (DFT) calculations with a 6-311 + G (d,p) basis set and the B3LYP exchange correlation functional predict that the carbon atoms α to either phenyl ring are the most likely sites of