Substituent parameters for radical reactions: Cerium(IV)‐substituted acetophenones–acrylonitrile system

Abstract

SynopsisThe present investigation describes a new approach for the determination of radical substituent parameters u.. The technique has been developed by an ingenious combination of two equations, one proposed by Yamamoto and Otsu and the other by Streitwieser and Perriri. The u.values for different substituents were first evaluated by application of this newly developed technique to the Ce(1V)-substituted toluenes-acrylonitrile system. The validity of these values was then tested by application to another system, the Ce( 1V)-substituted acetophenones-acrylonitrile system, which is the subject of the present study.Several attempts for the determination of the stabilizing ability of substituents in radical reactions (radical substituent parameters) have been made by different workers.Alfrey and Price' postulated the now famous Q-e equation, which related the reactivity ratios of monomers in binary copolymerization to two fundamental parameters Q and e for a given monomer and its corresponding radical.A general expression for the rate constants for reactions between a radical and a substrate has been developed by Bamford and Jenkim2 log k = log k3,T + a a + p The parameter a defines the polarity of the radical, and the parameters a and p are characteristics of the substrate.As a result of a number of studies, Timberlake et al.3-5 have reported their findings that no single substituent parameter like a, u+, u-, a~, and (TR, etc., can give the desired linear Hammett plot and have, therefore, recommended the use of multiparameter equations for Hammett p-a correlation.The use of multiparameter equations was first reported by Yukawa and Tsuno,G who have shown that a four-parameter modified form of the standard Hammett equation involving u+ and r improved the correlation obtained in aromatic electrophilic substitutions: log -= pa + r(u+a) (k", ) r(proportiona1ity constant) gives the contribution of the enhanced resonance effect for R substituent.

Novel jute yarns grafted with methyl methacrylate

“…Vinyl monomer can be grafted onto the jute fiber with different initiator systems, such as cerric salts. Cerric salts in aqueous acidic solution either by themselves5 or in combination with reducing agents6–8 graft the vinyl monomer onto natural and synthetic fibers. A number of studies have been conducted in the past to deal with the mechanism and the kinetics of graft copolymerization involving different monomers and natural fibers.…”