Question

Explain why using one or two equivalents of NaH results in different products in the following reactions.

Short answer

The acidic proton of the given compound is abstracted by the base NaH.The most stabilized carbanion gives the “most acidic proton.”

Step-by-step solution

Abstraction of proton from the base

The acidic proton of the given compound is abstracted by the base NaH.The most stabilized carbanion gives the “most acidic proton.”

Bimolecular reaction

If applied, the stabilized carbanion attacks the less substituted alkyl halide and forms the substituted product with the opposite stereochemistry.

Explanation

The first equivalent of NaH removes the most acidic proton, i.e., the OH proton on the phenol. The resulting phenoxide can then act as a nucleophile to displace I to form a substitution product.

With two equivalents, both OH protons are removed. The more nucleophilic O atom is the stronger base,i.e., the alkoxide derived from the alcohol (not the phenoxide).

So, this negatively charged O atom reacts first in a nucleophilic substitution reaction.

Reaction process