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Questions and Answers
What is the function of the carbonyl group in carbonyl compounds?
What is the reason for the acidity of α-hydrogens in carbonyl compounds?
What is the name given to the carbanions stabilized by the carbonyl carbon?
Which of the following is a common base used in reactions involving carbonyl compounds?
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Why are aldehydes stronger acids than ketones?
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What is the reason for the stabilization of the enolate ion?
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What is the effect of the carbonyl group on the acidity of α-hydrogens?
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Which of the following is NOT a characteristic of carbanions formed by ionization of α-hydrogens?
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What is the role of the carbonyl group in the aldol reaction?
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What is the intermediate formed in Step 1 of the aldol reaction?
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What is the final product of the aldol reaction?
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What is the role of the hydroxide ion in Step 1 of the aldol reaction?
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What is the key reactive intermediate in acid-catalyzed aldol condensations?
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What is the role of the protonated ketone in acid-catalyzed aldol condensations?
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What is the product of the acid-catalyzed aldol condensation?
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What is the role of the enol in acid-catalyzed aldol condensations?
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What is the reactant in the reaction that produces 1,1-diphenylethene?
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What is the role of triphenylphosphine in the reaction?
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What is the characteristic of phosphorus ylides?
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What is the product of the reaction between benzaldehyde and methylenetriphenylphosphorane?
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What is the condition required for the reaction to occur?
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What is the significance of the carbon-carbon double bond in the reaction?
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What is the reactant that reacts with triphenylphosphine to form a ylide?
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What is the product of the reaction between methylenetriphenylphosphorane and benzaldehyde?
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What is the reactant used to synthesize n-Butyl alcohol and 2-Ethyl-1-hexanol on an industrial scale?
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What is the catalyst used in the synthesis of 2-Ethyl-1-hexanol?
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What is the type of reagent used in the synthesis of unsaturated alcohols?
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What is the product of the reaction of acetaldehyde and hydrogen in the presence of a catalyst?
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What is the role of the catalyst in the synthesis of n-Butyl alcohol?
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What is the intermediate product formed in the synthesis of 2-Ethyl-1-hexanol?
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What is the purpose of using a chemoselective reagent in the synthesis of unsaturated alcohols?
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What is the catalyst used in the synthesis of n-Butyl alcohol?
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What is the purpose of using 2-oxazoline in the synthesis of substituted esters?
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What is the outcome of treating the 2-oxazoline with n-butyllithium?
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What is the reason behind the synthesis of substituted esters depending on the ease of formation and hydrolysis of 2-oxazolines?
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What is the product of the reaction between a primary amine and a carbonyl compound?
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What is the orientation of the elimination reaction in the formation of an imine?
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What happens to the enamine if it is formed initially in the reaction between a primary amine and a carbonyl compound?
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What is the difference between the reaction of a primary amine and a secondary amine with a carbonyl compound?
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What is the purpose of using enamines in organic synthesis?
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Study Notes
Carbonyl Group and Acidity
- The carbonyl group strengthens the acidity of hydrogen atoms attached to the α-carbon due to the presence of a highly electronegative oxygen atom.
- The presence of a base with a carbonyl compound that possesses an α-hydrogen leads to ionization of the latter, resulting in a carbanion.
- The carbanion is a resonance hybrid of two structures, made possible by the participation of the carbonyl group.
Enolate Anions
- Carbanions stabilized by a carbonyl carbon are known as enolate anions, which can exist in both keto and enol forms.
- The inductive effect of the positively polarized carbonyl carbon strongly stabilizes the negative charge at the α-position.
- Aldehydes are stronger acids than ketones because their carbonyl carbon bears a larger partial positive charge.
Aldol Reaction
- The aldol reaction involves the formation of a carbanion, which then attacks a carbonyl group, followed by protonation to form a β-hydroxyaldehyde.
- The carbonyl group plays two roles in this reaction: it provides the unsaturated linkage for the addition to occur, and it makes the α-hydrogen acidic enough for carbanion formation.
- The reaction can be illustrated for various compounds, such as propionaldehyde, phenylacetaldehyde, acetophenone, and cyclohexanone.
Acid-Catalyzed Aldol Condensations
- Acid-catalyzed aldol condensations typically give α,β-unsaturated carbonyl compounds as products, with the addition product not being isolated.
- The conjugate acid of the aldehyde or ketone is a key reactive intermediate, serving as a source of the enol and as the electrophilic species in the reaction.
Synthesis of Unsaturated Alcohols
- Unsaturated alcohols can be synthesized using a reagent that reduces only the carbonyl group, leaving the carbon-carbon double bond intact, such as sodium borohydride (NaBH4).
- This is an example of a chemoselective reagent, which selectively attacks one of several different functional groups.
Protection of Carboxyl Groups
- The reaction of a phosphorus ylide with an aldehyde or ketone can be used to protect the carboxyl group, with the position of the carbon-carbon double bond being maintained.
- The phosphorus ylides have hybrid structures, with the negative charge on carbon and the positive charge on phosphorus.
Alkylation of Carbonyl Compounds via Enamines
- Amines react with carbonyl compounds by nucleophilic addition, with the initial addition product undergoing dehydration to form a compound containing a carbon-nitrogen double bond (an imine).
- If the amine is primary, the preferred product is the imine, while if the amine is secondary, the product is an enamine.
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Description
The carbonyl group's influence on the acidity of hydrogen atoms attached to the α-carbon, and its role in ionization. Learn about the resonance hybrid structures formed in this process.