Nucleophilic addition and substitution mechanism steps for aldehydes, ketones, and carboxylic acid derivatives, distinct from the reagent-matching focus of the reactions and reagents deck.
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- What is the geometry of a carbonyl carbon before a nucleophile attacks it?
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sp2, trigonal planar.- What is the geometry of the carbonyl carbon after a nucleophile adds to it?
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sp3, tetrahedral.- In base-catalyzed nucleophilic addition to a carbonyl, what happens in the first step?
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The nucleophile attacks the electrophilic carbonyl carbon, and the pi electrons shift onto oxygen to form an alkoxide intermediate.- In base-catalyzed nucleophilic addition to a carbonyl, what happens in the second step?
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The alkoxide intermediate is protonated to give the neutral alcohol product.- In acid-catalyzed nucleophilic addition to a carbonyl, what is the first mechanistic step?
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Protonation of the carbonyl oxygen by the acid catalyst.- Why does protonating the carbonyl oxygen speed up nucleophilic addition?
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It puts a full positive charge on the carbonyl group, making the carbon much more electrophilic.- Why do aldehydes generally react faster than ketones toward nucleophilic addition?
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Aldehydes have only one alkyl or H group, so there is less steric hindrance and less electron donation to the carbonyl carbon than in ketones.- What is a hemiacetal?
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The product of one equivalent of alcohol adding to an aldehyde or ketone carbonyl, bearing both an OH and an OR group on the same carbon.- What additional step converts a hemiacetal into a full acetal?
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Acid-catalyzed loss of water followed by attack of a second equivalent of alcohol.- What cationic intermediate forms when water leaves the protonated hemiacetal during acetal formation?
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A resonance-stabilized oxocarbenium ion.- In acetal formation, what attacks the oxocarbenium ion intermediate?
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The second equivalent of alcohol.- What nucleophile attacks the carbonyl carbon in cyanohydrin formation?
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Cyanide ion.- What is the product after the alkoxide intermediate is protonated in cyanohydrin formation?
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A beta-hydroxy nitrile.- What is the first mechanistic step in imine formation from a primary amine and a carbonyl compound?
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The amine nitrogen's lone pair attacks the carbonyl carbon, forming a tetrahedral carbinolamine (hemiaminal).- What is the final mechanistic step in imine formation after the carbinolamine forms?
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Acid-catalyzed dehydration, protonating and eliminating water to form the C=N double bond.
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