Question

If we add HI to a substrate Ph-C-C-OH what will be the major product and what reaction mechn. will be followed?

My attempt: as -OH is bad Leaving Group, we cannot just simply proceed with Sn2 and remove the OH. So first H2O (due to the H+ and lone pair on O) will form and then it will leave the substrate and then 1-2 hydride shift in Ph-C-C+ --> Ph-(C+)-C and we will add I- at the carbocation.
My dilemma is how can we even form a 1* carbocation (even if it can be stabilised by rearrangement )
Is my attempt valid? If not what would be the real mechanism and why?

Answer 1

The major product is Ph-C-C-I and the reaction follows an SN1 mechanism.

Step-by-step explanation:

The major product formed by the addition of HI to the substrate Ph-C-C-OH is Ph-C-C-I. The reaction follows an SN1 (substitution, nucleophilic, unimolecular) mechanism.

The OH group in the substrate is converted to a good leaving group by reacting with HI to form H2O, which then leaves the substrate. The resulting carbocation undergoes a 1-2 hydride shift, and then I- adds to the carbocation to form the final product.