Substituents In Para Position Research Articles

Substituent effects on some physicochemical properties of chalcones and their vinylogues

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.

Quantitative I.R.-messungen an p-substituierten polystyrolen

Using the KBr disk technique we have measured the infra-red spectra of the poly( p-halogene styrenes), of poly( p-methyl styrene) and of poly( p-iso-propyl styrene). With all polymers, excepted the fluorine derivative, measurements were also made with CS 2 solutions. The absorptivities (ϵ max and ƒϵ dλ) of the following aromatic hydrogen vibrations were determined: out-of-plane vibration at about 830 cm −1, δ s (in-plane) at about 1010 cm −1, and δ as(in-plane) in the region between 1165 cm −1 and 1055 cm −1. In the case of δ s , ƒϵ dλ increases strongly from the fluorine derivative to the chlorine derivative; the absorptivities of δ as move in the opposite direction, the fluorine compound being an exception. As to the out-of-plane vibration, there are only slight differences. In the case of δ s and δ as , ƒϵ dλ and λ max depend on the molecular weight of the substituent in para position. The wave numbers of all aromatic hydrogen vibrations of the halogene derivatives increased from the iodine to the fluorine compound. Due to the non-ideal dispersion of the polymer in the KBr, ϵ max. (KBr) is always smaller than ϵ max (CS 2). The preparation technique described allows reproducible values for ϵ max (KBr). ƒϵ dλ depends little on the preparation technique. There is some evidence about an influence of the polar KBr on ϵ max.