B. M. Wepster

Substituent effects in π-(Tricarbonylchromium) arenes

Abstract The thermodynamic dissociation constants of a series of 38 substituted π-(tricarbonylchromium)benzoic acids in 50% aqueous ethanol at 25°C have been determined. The results require revision of some literature values. The p K a * -values of the π-(tricarbonylchromium)benzoic acids were correlated with the electronic substituent parameters in terms of the Yukawa-Tsuno equation. The reaction constant (ρ) decreases from 1.4 for the benzoic acids to 0.8 for the π-(tricarbonylchromium)benzoic acids, reflecting the decreased ability of the complexed aromatic system to transmit electronic substituent effects. For the alkylsubstituted π-(tricarbonylchromium)benzoic acids, conformational effects of the Cr(CO) 3 group can account for some of the anomalies observed. The substituent parameters, σ meta and σ para , of the π-(Cr(CO) 3 )phenyl group as a substituent were derived from the dissociation constants of the complexed phenylbenzoic acids.

Chemistry of neopentyl derivatives : I. Ambidency of the benzyl grignard reagent in reaction with t-butyl halides. Synthesis and thermodynamic dissociation constants of neopentylbenzoic acids

Abstract The reaction of benzylmagnesium halides with t-butyl halides yields o - and p -t-butyltoluene in addition to neopentylbenzene. A study has been made of the influence of (i) the halide atoms present in both reactants, (ii) the purity of the magnesium used, (iii) the solvent in which the reaction is conducted, and (iv) the substituents in the aromatic ring of the benzyl Grignard reagent. The reaction of t-butyl- magnesium chloride with 4-alkylbenzyl chlorides has also been investigated. The neopentyltoluenes can be oxidized selectively to the corresponding neopentylbenzoic acids. The p K * a -values of these acids have been determined in 50 vol % EtOH and are compared with those of sixteen other monoalkyl-substituted benzoic acids.