Propose mechanisms for the following reactions. Additional products may be formed, but your mechanism only needs to explain the products shown.

The given reactant on reaction with methanol undergoes S_N1 reaction and forms carbocation in the first step. This carbocation formed is tertiary and stable, so no rearrangement occurs. In the next step, methanol acts as a nucleophile and attacks carbocation and after loss of proton, the S_N1 product is formed. Also, E1 elimination reaction can occur, and alkene formation is a possibility. Proton abstraction from adjacent carbons of carbocation leads to formation of alkene in which one alkene is more substituted than the other.

Formation ofS_N1 product and E1 products

The given reactant in the presence of acidic medium undergoes proton abstraction in the first step as oxygen of hydroxyl acts as a good base. It abstracts proton from the medium and gets converted to a good leaving group—water. Leaving group leaves in the next step on heating and carbocation forms, which is unstable as it is primary and undergoes rearrangement reaction. For example, hydride shift and alkyl shift ring expansion to give products, and since it is a dehydration mechanism, alkene products are formed.

After hydride shift, two products are possible—exocyclic and endocyclic alkene.

Formation of different alkenes through rearrangements and dehydration mechanism

The given reactant forms carbocation when treated with ethanol which is followed by heating. This carbocation can undergo resonance and there are three possible paths through which products can be obtained. Ethanol acts as a nucleophile as well as base and attacks the carbocation. After charge neutralisation, we get one alkene product and two substitution products.

Formation of substitution and elimination products