Substituent effects on some physicochemical properties of chalcones and their vinylogues

Abstract

Carbonyl stretching frequencies (ν CO), dipole moments (μ), longwave maxima (λ max), half-wave potentials (° 1/2), and relative intensities ( Z/ Z 0) of benzoyl-ion in mass-spectra of trans chalcones and their vinylogues of the general type PhCO(CH=CH) nC 6H 4R-p (I) were measured. Contrary to the previously investigated polyenes of the type R(CH=CH) nR′ (R′ = CHO or COOEt) variation of the substituent R in compounds I has little influence on properties of I in the ground state and a satisfactory linear relationship between (ν CO) or μ and σ constants exists only in the case of I (n = 0, 1); the best correlation with σ + indicates that the mesomeric mechanism plays a great part in the transmission of electronic effects. λ max., E 1/2, or Z/ Z 0 of all series I (n = 0–3) correlate with σ p or σ 0 constants, and the separation of mesomeric and inductive effects by multiparametric correlation reveals that in this case inductive effect is of great importance in the transmission of electronic effects. These features were accounted for by the non-planar structure of molecules of I, which was confirmed by X-ray analysis of I (R = Br). The Pariser-Parr-Pople method has also been applied to the calculation of π-electronic density in molecules I and it was found that the introduction of various substituents in para position of I exercises a very little influence on the electronic distribution in compounds I.