Question

$ S_N1 $ reaction is favoured by:
(A) non- polar solvents
(B) bulky group on the carbon atom attached to the halogen atom
(C) small groups on the carbon atom attached to halogen atom
(D) All the above

Answer 1

Hint : $ {{S}_{N}}1 $ reaction is a stepwise reaction in which first the carbocation is formed and the removal of the leaving group, after which the nucleophile attack the carbocation and then deprotonation of protonated nucleophile takes place giving us the product.

Complete Step By Step Answer:
 $ {{S}_{N}}1 $ reaction is an organic nucleophilic substitution reaction.
In this reaction, a carbocation intermediates forms.
Since this reaction proceeds by carbocation formation so the stability of carbocation will favour the $ {{S}_{N}}1 $ mechanism.
The stability of carbocation depends on three main factors:
1. The neighboring carbon atoms.
2. The neighboring carbon-carbon multiple bonds.
3. The neighboring atoms with lone pairs.
The stability of carbocation increases from primary to tertiary carbon atoms. One of the reasons for this can be that if the neighboring carbon atom is electron rich it will be able to donate the electrons to the carbocation. Another reason for this can be hyperconjugation, which is the stability through donation of C-H sigma bond to the empty p orbital.
Hence, we can conclude that a bulky group on the carbon atom attached to the halogen atom will increase the stability of carbocation which will favour the $ {{S}_{N}}1 $ reaction.

Note :
There are many other factors affecting the stability of carbocation( stated above) that will also affect the $ {{S}_{N}}1 $ reaction so make sure to keep them also in mind while a complete reaction.