Introduction:

SN1 reaction is a nucleophilic substitution reaction in which the rate-determining step is the formation of a carbocation intermediate. The reactivity of a substrate towards an SN1 reaction depends on various factors such as the stability of the carbocation intermediate, the strength of the leaving group, and the solvent used.

Stability of carbocation intermediate:

Carbocation intermediates are highly unstable and tend to undergo rearrangement to form a more stable carbocation. Therefore, substrates that can form a more stable carbocation intermediate are more reactive towards SN1 reaction. For example, tertiary carbocations are more stable than secondary and primary carbocations. Hence, tertiary substrates are more reactive towards SN1 reaction than secondary and primary substrates.

Strength of the leaving group:

The strength of the leaving group determines the ease with which it can dissociate from the substrate. A good leaving group is one that can stabilize the negative charge that is formed after its dissociation. Therefore, substrates with better leaving groups are more reactive towards SN1 reaction. For example, halogens such as iodine, bromine, and chlorine are good leaving groups. Hence, substrates with these leaving groups are more reactive towards SN1 reaction than those with weaker leaving groups.

Solvent:

The solvent used also plays a crucial role in determining the reactivity of a substrate towards SN1 reaction. Polar protic solvents such as water and alcohols stabilize the carbocation intermediate by solvating it. Therefore, substrates that form stable carbocation intermediates are more reactive in polar protic solvents. On the other hand, polar aprotic solvents such as acetone and DMF do not solvate the carbocation intermediate. Therefore, substrates that form less stable carbocation intermediates are more reactive in polar aprotic solvents.

Conclusion:

In summary, substrates that can form stable carbocation intermediates, have good leaving groups, and are used in polar protic solvents are more reactive towards SN1 reactions. Tertiary substrates with good leaving groups such as iodine, bromine, and chlorine are the most reactive towards SN1 reaction.

In SN1 carbocation is formed so more is the stable carbocation mote is the reactive substrate.