Question

Arrange these alkyl iodides according to decreasing rates of their sn1 reactions?

1) Methyl iodide
2) Ethyl iodide
3) Isopropyl iodide
4) Tert-butyl iodide

Answer 1

The SN1 reaction rates for alkyl iodides are determined by the stability of the carbocation formed. Tert-butyl iodide reacts the fastest followed by isopropyl iodide, ethyl iodide, and then methyl iodide, in decreasing order of the reaction rate.

Step-by-step explanation:

The SN1 reaction rates of alkyl iodides depend on the stability of the carbocation intermediate formed during the reaction. In general, the more substituted the central carbon is, the more stable the carbocation, and the faster the SN1 reaction will proceed. Using this principle, we can arrange the given alkyl iodides according to the decreasing rates of their SN1 reactions as follows:

1. Tert-butyl iodide [(CH3)3CI] - This has a tertiary carbon attached to the iodine and will form the most stable carbocation upon ionization, leading to the fastest SN1 reaction.
2. Isopropyl iodide [(CH3)2CHI] - This has a secondary carbon and will form a less stable carbocation than tert-butyl iodide, leading to a slower SN1 reaction.
3. Ethyl iodide [CH3CH2I] - With a primary carbon, ethyl iodide will form a carbocation that is less stable than the isopropyl carbocation, thus it has a slower reaction rate.
4. Methyl iodide [CH3I] - Methyl iodide can form only a primary carbocation, which is the least stable and gives the slowest SN1 reaction among the listed compounds.