Effect of solvents and nucleophiles on the reactivity of allyl bromide-A kinetic study

The kinetics of the reaction of allyl bromide with benzoyl thiosemicarbazide has been studied in different protic and aprotic solvents. Correlation of rate constants with different solvent parameters applying linear multiple regression analysis indicates that the non-specific solvent parameters Y, P and nucleophilicity , S, influence the rate of nucleophilic substitution. Using these solvent parameters. the linear solvation energy relationship is derived. Study of the reaction with substituted thiosemicarbazides indicates that structural effects on rate of the reaction are minimal. Solvent effects on organic reactivity are as important as structural effects. A solvent can influence the rate of any reaction by solvating the reactants and the transition state due to polar effects. The solvent is considered as a homogeneous isotropic continuum which surrounds the solute molecule. The intensity of solvent-solute interactions is expressed in terms of macroscopic physical properties of the solvent like dielectric constant, refractive index and other molecular characteristics. Solvent effects caused by such long-range intermolecular forces are called non­ specific solvent-solute interactions. A solvent can also exert short-range interactions on solute through donor-acceptor bonds. These are called specific solvent-solute interactions. During these interactions, a solvent can accept or donate electrons from or to the solute causing electrophilic or nucleophilic solvation. Further, solvent can also form hydrogen bonds with the solute. So, the general term solvation means forming a solvent shell around the solute due to either all of these or some of these interactions. Therefore any solvent dependent property 'X' can be expressed as