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Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
All textbooksMullins 1st EditionCh. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid DerivativesProblem 2
Chapter 18, Problem 2

Would you expect a ketone or an ester to be more reactive with a strong nucleophile? Justify your answer.
Chemical structures of a ketone and an ester, illustrating their reactivity with strong nucleophiles.

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Step 1: Analyze the chemical structures provided in the image. The left structure is a ketone (benzyl methyl ketone), characterized by a carbonyl group (C=O) directly bonded to two carbon atoms. The right structure is an ester (ethyl benzoate), characterized by a carbonyl group (C=O) bonded to an oxygen atom and a carbon atom.
Step 2: Understand the reactivity of ketones and esters with nucleophiles. Ketones have a carbonyl group that is more electrophilic because the carbonyl carbon is directly bonded to two carbon atoms, which do not significantly stabilize the partial positive charge on the carbonyl carbon. Esters, on the other hand, have an oxygen atom bonded to the carbonyl carbon, which can donate electron density through resonance, reducing the electrophilicity of the carbonyl carbon.
Step 3: Consider steric factors. Ketones generally have less steric hindrance around the carbonyl carbon compared to esters, which have an additional alkoxy group. This makes the ketone more accessible to nucleophiles.
Step 4: Evaluate the leaving group ability. In esters, the alkoxy group (-OR) can act as a leaving group during nucleophilic attack, which can stabilize the intermediate formed. Ketones do not have a good leaving group, so the reaction mechanism differs, and the intermediate is less stabilized.
Step 5: Conclude based on the above factors. Ketones are generally more reactive with strong nucleophiles compared to esters due to their higher electrophilicity and lower steric hindrance. Esters are less reactive because of resonance stabilization and the presence of a leaving group that alters the reaction pathway.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Nucleophilicity

Nucleophilicity refers to the ability of a nucleophile to donate an electron pair to an electrophile. Strong nucleophiles, such as alkoxides or hydrides, are more reactive and can effectively attack electrophilic centers in organic molecules. Understanding the strength and nature of nucleophiles is crucial for predicting reaction outcomes in organic chemistry.
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Electrophilicity of Carbonyl Compounds

Both ketones and esters contain carbonyl groups (C=O), but their electrophilicity differs. Ketones have two alkyl groups attached to the carbonyl carbon, which can stabilize the positive charge during nucleophilic attack, making them less reactive. In contrast, esters have an alkoxy group that can withdraw electron density, making the carbonyl carbon more electrophilic and thus more reactive towards nucleophiles.
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Mechanism of Nucleophilic Addition

The mechanism of nucleophilic addition involves the nucleophile attacking the electrophilic carbon of the carbonyl group, leading to the formation of a tetrahedral intermediate. This process is influenced by the steric and electronic properties of the substituents on the carbonyl carbon. Understanding this mechanism helps in predicting the reactivity of ketones and esters with strong nucleophiles.
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Related Practice
Textbook Question

Provide the IUPAC name for the following molecules.

(d)

1
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Textbook Question

Which of the following are considered carboxylic acid derivatives?

(a)

1
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Textbook Question

Rank the following anions based on their stability as potential leaving groups. Explain your reasoning (1 = most stable ; 5 = least stable).

9
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Textbook Question

Provide the IUPAC name for the following molecules.

(e)