Ketones react with sodium acetylide (the sodium salt of acetylene, .Na^+-: C ≡CH) to give alcoho

step 1 Today we are told that two butanone can react with sodium acetylide in order to produce alcohols

Ketones react with sodium acetylide (the sodium salt of...

Ketones react with sodium acetylide (the sodium salt of acetylene, $\left.\mathrm{Na}^{+-}: \mathrm{C} \equiv \mathrm{CH}\right)$ to give alcohols. For example, the reaction of sodium acetylide with 2 -butanone yields 3 -methyl-1-pentyn-3-ol: (a) Is the product chiral? (b) Assuming that the reaction takes place with equal likelihood from both $R e$ and $S i$ faces of the carbonyl group, is the product optically active? Explain.

Ketones react with sodium acetylide (the sodium salt of acetylene, $\left.\mathrm{Na}^{+-}: \mathrm{C} \equiv \mathrm{CH}\right)$ to give alcohols. For example, the reaction of sodium acetylide with 2 -butanone yields 3 -methyl-1-pentyn-3-ol:
(a) Is the product chiral?
(b) Assuming that the reaction takes place with equal likelihood from both $R e$ and $S i$ faces of the carbonyl group, is the product optically active? Explain.

Key Concepts

Optical Activity

Optical activity is the ability of chiral molecules to rotate the plane of polarized light. A pure enantiomer will rotate light in a specific direction (clockwise or counterclockwise), while a racemic mixture, which contains equal amounts of both enantiomers, will show no net rotation because the effects cancel out.

Nucleophilic Addition to Carbonyl Compounds

Nucleophilic addition to carbonyl compounds is a fundamental reaction mechanism in organic chemistry where a nucleophile attacks the electrophilic carbon of the carbonyl group. This attack typically results in the formation of an alkoxide intermediate, which upon protonation, yields an alcohol. If the carbonyl carbon becomes a stereocenter during this process, chirality is introduced into the molecule.

Chirality

Chirality refers to the geometric property of a molecule that makes it non-superimposable on its mirror image. It usually arises when a carbon atom is bonded to four different substituents, creating a stereogenic center. In many organic reactions, the creation or alteration of such centers is a key concern as it influences both the physical and chemical properties of the molecule.

Stereofacial Selectivity and Racemic Mixture Formation

In reactions involving planar carbonyl groups, the nucleophile can attack from either the Re face or the Si face. When both faces are equally accessible, the reaction yields equal amounts of the two enantiomers, leading to a racemic mixture. Despite each individual enantiomer being chiral, the overall product is optically inactive due to the cancellation of optical rotations.

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