Q.40. - Organic Chemistry

Question

Question: Explain the observed rate of reactivity of the following $\mathbf{2}\mathbf{°}$alkyl halides in an ${\mathit{S}}_{\mathbf{N}}\mathbf{1}$ reaction.

Step-by-Step Solution

Answer

Answer

Step 1: Alkyl halides

Halogen atoms are used instead of one or several hydrogen atoms in compounds termed alkyl halides. Some examples of alkyl halides are methyl chloride and 2-chloropropane.

Step 2: S N 1 reaction

The carbocation intermediate has a primary role in the ${\mathit{S}}_{\mathbf{N}}\mathbf{1}$  reaction. Compounds generating highly stable intermediates are more reactive than those generating less stable ones.

Step 3:Reactivity of the secondary alkyl halides in an S N 1 reaction

The stability of carbocation influences the rate of an $S_{N}1$ reaction

The first compound has $4\mathrm{\pi }$ electrons and is aromatic. It produces an unstable intermediate, and it can be given as:

Carbocation generated from the first compound

The carbocation generated from the second compound can be given as:

Carbocation generated from the second compound

The third compound has $6\mathrm{\pi }$ electrons and is aromatic. It gives rise to a very stable intermediate as:

Carbocation generated from the third compound

The increasing reactivity of the alkyl halides can be given as:

Increasing reactivity of alkyl halides

In the third compound, the aromatic carbocation is delocalized over the whole ring, making it a stable intermediate. Hence it can be easily formed in an $S_{N}1$ reaction.