between elimination reaction and nucleophilic substitution reaction which one requires highest activation energy for the reaction to take to place?? and why??
39Elimination reactions have greater free energies of activation than substitution reactions. This is because more bonding changes occur in elimination than in substitution. When a higher temperature is used, according to chemical kinetics, the fraction of molecules whose energy is in excess of activation energy(called the Boltzmann factor, e-Ea/RT) increases for both elimination and substitution reactions, but the increase for elimination is substantially more than that for substitution.
This is because elimination is entropically favoured to substitution. The products of an elimination reaction are greater in number than the reactants(recall chemical thermodynamics concepts), hence the higher change in entropy.
The equation dG = dH - TdS you must be knowing. With a high temperature and higher change in entropy, eliminations are thus favoured at higher temperatures(though when we decide elimination Vs substitution, many other factors are taken into regard, because all bases are potential nucleophiles and vice-versa).
391. A nucleophile is any electron rich species which loves attacking positively charged(partial or full, as is the case) carbon atoms. A base is a species which abstracts any positively charged species(mostly protons or deuterons)
2. A base's strength is defined by its own equilibrium constant Kb. A nucleophile's strength is defined by the reaction's rate constant. Both are different.
