Which of these could be a nucleophile for a Claisen Condensation? (select all that apply)

Question

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To determine which species could act as a nucleophile in a Claisen Condensation, recall that the nucleophile is typically an enolate formed from a carbonyl compound that has an alpha proton, which can be deprotonated to give a resonance-stabilized anion.
Option A: aldehyde with alpha H
Reasoning: Aldehydes can form enolates if there are alpha hydrogens, but in classical Claisen condensations the nucleophile is an enolate derived from an ester (not an aldehyde). Aldehydes are more commonly electrophiles in related reactions (e.g., aldol condensations) rather than serving as nucleophiles in a standard Claisen. Therefore this option is not considered a typical Claisen nucleophile.
Option B: aldehyde with no alpha H
Reasoning: Without any alpha hydrogens, the aldehyde cannot form an enolate, so it cannot act as a nucleophile in a Claisen. This makes this option unsuitable.
Option C: ketone with no alpha H
Reasoning: A ketone lacking alpha hydrogens cannot form an enolate, so it cannot serve as the nucleophile in a Claisen condensation. This option is incorrect.
Option D: ketone with 2+ alpha H
Reasoning: A ketone that has alpha hydrogens can be deprotonated to give a ketone enolate. While most classic Claisen condensations use esters as nucleophiles, the question explicitly accepts ketones with alpha hydrogens as potential nucleophiles in a Claisen-type context. Thus this option is considered correct in the provided answer key.
Option E: ester with 2+ alpha H
Reasoning: An ester with alpha hydrogens readily forms an ester enolate, which is the quintessential nucleophile in a canonical Claisen condensation (where the enolate attacks another ester). This is a textbook correct choice.
Option F: ester with 1 alpha H
Reasoning: Even a single alpha hydrogen is enough to form an enolate on an ester under basic conditions, so this ester could act as a nucleophile as well. Although the key provided lists only the 2+ alpha H ester as correct, in many contexts an ester with at least one alpha H is capable of enolate formation and nucleophilic attack. Hence this is a nuanced case; it could be considered correct in broader teaching, but the given key marks it as not.
Option G: ester with no alpha H
Reasoning: Without any alpha hydrogens, the molecule cannot form an enolate and cannot serve as a nucleophile in a Claisen condensation. This option is incorrect.
Option H: carboxylic acid with alpha H
Reasoning: Carboxylic acids do not form the necessary enolate under typical Claisen conditions, and their alpha hydrogens (if present in the corresponding alpha carbon) are not in a form that enables the Claisen nucleophilic attack. This makes it incorrect.
Option I: carboxylic acid with no alpha H
Reasoning: Absence of alpha hydrogens means no enolate formation; thus it cannot act as a Claisen nucleophile. This option is incorrect.

CHE 008B A01 SS1 2025 Lecture 14 - Claisen Condensation

Which of these could be a nucleophile for a Claisen Condensation? (select all that apply)

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