Home
Class 12
CHEMISTRY
Nucleophilic substitution reactions gene...

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 negative 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) polarise able 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`.

Text Solution

Verified by Experts

The correct Answer is:
D
Promotional Banner

Similar Questions

Explore conceptually related problems

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 negative 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) polarise able 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 feasible?

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) polarise able 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. (I) CI^(-) (II) CH_(3)O^(-) (III) CH_(3)S^(-) (IV) I^(-) The correct order of increasing leaving group capability of above anions

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 negative 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) polarise able 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. (I) CH_(3)Br (II) CH_(3)F (III) CH_(3)OH (IV) CH_(3)OSO_(2)CF_(3) The correct order of decreasing reactivity of the above compounds towards CH_(3)O^(-) in an S_(N)2 reaction is: