Nucleophilic substitution reactions generally expressed as
`Nu^(-) +R-L rarr R-Nu +L^(-)`
Where `Nu^(-) rarr` Nucleophile , `R-L rarr` substrate, `L rarr` leaving group
The best leaving groups are those that become the most stable ions after they depart. since most leaving group leave as a negatibe ion, the best leaving groups are those ions that stabilize a negative charge most effectively. A good leaving group should be
(a) electron-withdrawing to polarize the carbon
(b) stable once it has left (not a strong base)
(c) polaristable to maintain partial bonding with the carbon in the transition state (both `S_(N)1` and `S_(N)2)`. This bonding helps to stabilise the transition state and reduces the activation energy.
Among the following which is false statement?
A. The weaker the base after the group departs, the better the leaving group
B. A reactive leaving group would raise the energy of the product, driving the equilibrium towards the reactants
C. Relative leaving group ability may very with change of solvent.
D. Better leaving group only increases `S_(N)2` rate, not `S_(N)1`.
