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Give reasons for the following: (CH3)3C–O–CH3 on reaction with HI gives (CH3)3C–I and CH3–OH as the main products and not (CH3)3C–OH and CH3–I. - Chemistry

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 Give reasons for the following:

(CH3)3C–O–CH3 on reaction with HI gives (CH3)3C–I and CH3–OH as the main products and not (CH3)3C–OH and CH3–I.

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Solution 1

Usually, iodide, being a big nucleophile, attacks on the group with low steric hindrance and the reaction proceeds by SN2 mechanism.

However, in this case, methanol, on leaving generates a tertiary carbocation, which is more stable. Hence, this reaction proceeds by SN1 mechanism and therefore, we get (CH3)3C-I and CH3-OH as the major products.

Solution 2

CH3)3-C–O–CH3 is an ether with two different alkyl groups, of which (CH3)3-C-, a tertiary alkyl group, on reaction with hydrogen halide (HI) forms a tertiary halide. This occurs as the reaction is an SN1 reaction. The reaction involves the formation of a stable carbocation. If the ether has a primary alkyl group, then the reaction follows the SN2 mechanism.

Concept: Hydrocarbons: Alkanes - Reactions of Haloalkanes - Nucleophilic Substitution Reactions
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