SN 1 reaction in haloarenes..
Answers
Answer:
The SN1 reaction is a substitution nucleophilic unimolecular reaction. It is a two-step reaction. In the first step, The carbon-halogen bond breaks heterolytically with the halogen retaining the previously shared pair of electrons. In the second step, the nucleophile reacts rapidly with the carbocation that was formed in the first step.
This reaction is carried out in polar protic solvents such as water, alcohol, acetic acid etc. This reaction follows first order kinetics. Hence, this is named as substitution nucleophilic unimolecular. This reaction takes place in two steps as described below.
Step-1:
a) The bond between carbon and halogen breaks due to the presence of a nucleophile and formation of carbocation takes place.
b)It is the slowest and the reversible step as a huge amount of energy is required to break the bond.
c)The bond is broken by solvation of the compound in a protic solvent, thus this step is slowest of all.
d) The rate of reaction depends only on haloalkane, not on nucleophile.
Step-2:
a) The nucleophile attacks the carbocation formed in step 1 and the new compound is formed.
b) Since, the rate defining step of the reaction is the formation of a carbocation, hence greater the stability of formation of an intermediate carbocation, more is the ease of the compound undergoing substitution nucleophilic unimolecular or SN1 reaction.
c) In the case of alkyl halides, 3o alkyl halides undergo SN1 reaction very fast because of the high stability of 3o carbocations.
d) Hence allylic and benzylic halides show high reactivity towards the SN1 reaction.