Carbonyl Group's Effect on Acidity
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Questions and Answers

What is the function of the carbonyl group in carbonyl compounds?

  • It acts as an electron donating group
  • It only affects the acidity of β-hydrogens
  • It acts as an electron withdrawing group (correct)
  • It has no effect on the acidity of the hydrogen atoms

    • What is the reason for the acidity of α-hydrogens in carbonyl compounds?

  • Due to the inductive effect of the carbonyl carbon
  • Due to the presence of a negatively charged oxygen atom
  • Due to the presence of a highly electronegative oxygen atom (correct)
  • Due to the presence of a positively charged carbon atom

    • What is the name given to the carbanions stabilized by the carbonyl carbon?

  • Carboxylate anion
  • Keto anion
  • Alkoxide anion
  • Enolate anion (correct)

    • Which of the following is a common base used in reactions involving carbonyl compounds?

    <p>All of the above</p> Signup and view all the answers

    Why are aldehydes stronger acids than ketones?

    <p>Aldehydes have a larger partial positive charge on the carbonyl carbon</p> Signup and view all the answers

    What is the reason for the stabilization of the enolate ion?

    <p>All of the above</p> Signup and view all the answers

    What is the effect of the carbonyl group on the acidity of α-hydrogens?

    <p>It increases the acidity of α-hydrogens</p> Signup and view all the answers

    Which of the following is NOT a characteristic of carbanions formed by ionization of α-hydrogens?

    <p>They can be formed by ionization of β-hydrogens</p> Signup and view all the answers

    What is the role of the carbonyl group in the aldol reaction?

    <p>To make the α-hydrogen acidic enough for carbanion formation</p> Signup and view all the answers

    What is the intermediate formed in Step 1 of the aldol reaction?

    <p>Carbanion</p> Signup and view all the answers

    What is the final product of the aldol reaction?

    <p>A β-hydroxyketone</p> Signup and view all the answers

    What is the role of the hydroxide ion in Step 1 of the aldol reaction?

    <p>To abstract a hydrogen ion from the α-carbon</p> Signup and view all the answers

    What is the key reactive intermediate in acid-catalyzed aldol condensations?

    <p>The conjugate acid of the aldehyde or ketone</p> Signup and view all the answers

    What is the role of the protonated ketone in acid-catalyzed aldol condensations?

    <p>To react as an electrophile with the enol</p> Signup and view all the answers

    What is the product of the acid-catalyzed aldol condensation?

    <p>An α,β-unsaturated carbonyl compound</p> Signup and view all the answers

    What is the role of the enol in acid-catalyzed aldol condensations?

    <p>To react as a nucleophile with the protonated ketone</p> Signup and view all the answers

    What is the reactant in the reaction that produces 1,1-diphenylethene?

    <p>Benzophenone</p> Signup and view all the answers

    What is the role of triphenylphosphine in the reaction?

    <p>It is a reactant that forms a ylide</p> Signup and view all the answers

    What is the characteristic of phosphorus ylides?

    <p>They have a hybrid structure with a negative charge on carbon</p> Signup and view all the answers

    What is the product of the reaction between benzaldehyde and methylenetriphenylphosphorane?

    <p>1,1-diphenylethene</p> Signup and view all the answers

    What is the condition required for the reaction to occur?

    <p>Mild conditions</p> Signup and view all the answers

    What is the significance of the carbon-carbon double bond in the reaction?

    <p>Its position is not in doubt</p> Signup and view all the answers

    What is the reactant that reacts with triphenylphosphine to form a ylide?

    <p>Benzaldehyde</p> Signup and view all the answers

    What is the product of the reaction between methylenetriphenylphosphorane and benzaldehyde?

    <p>1,1-diphenylethene</p> Signup and view all the answers

    What is the reactant used to synthesize n-Butyl alcohol and 2-Ethyl-1-hexanol on an industrial scale?

    <p>Both acetaldehyde and n-butyraldehyde</p> Signup and view all the answers

    What is the catalyst used in the synthesis of 2-Ethyl-1-hexanol?

    <p>Cu, 250°C</p> Signup and view all the answers

    What is the type of reagent used in the synthesis of unsaturated alcohols?

    <p>Chemoselective reagent</p> Signup and view all the answers

    What is the product of the reaction of acetaldehyde and hydrogen in the presence of a catalyst?

    <p>n-Butyl alcohol</p> Signup and view all the answers

    What is the role of the catalyst in the synthesis of n-Butyl alcohol?

    <p>To reduce the reactant</p> Signup and view all the answers

    What is the intermediate product formed in the synthesis of 2-Ethyl-1-hexanol?

    <p>Adol product</p> Signup and view all the answers

    What is the purpose of using a chemoselective reagent in the synthesis of unsaturated alcohols?

    <p>To selectively reduce the carbonyl group</p> Signup and view all the answers

    What is the catalyst used in the synthesis of n-Butyl alcohol?

    <p>H2, Ni</p> Signup and view all the answers

    What is the purpose of using 2-oxazoline in the synthesis of substituted esters?

    <p>To protect the carboxyl group</p> Signup and view all the answers

    What is the outcome of treating the 2-oxazoline with n-butyllithium?

    <p>Formation of the lithio derivative</p> Signup and view all the answers

    What is the reason behind the synthesis of substituted esters depending on the ease of formation and hydrolysis of 2-oxazolines?

    <p>The 2-oxazoline ring is easily formed and hydrolyzed</p> Signup and view all the answers

    What is the product of the reaction between a primary amine and a carbonyl compound?

    <p>An imine</p> Signup and view all the answers

    What is the orientation of the elimination reaction in the formation of an imine?

    <p>The orientation is towards the formation of an imine</p> Signup and view all the answers

    What happens to the enamine if it is formed initially in the reaction between a primary amine and a carbonyl compound?

    <p>It tautomerizes into the more stable imino form</p> Signup and view all the answers

    What is the difference between the reaction of a primary amine and a secondary amine with a carbonyl compound?

    <p>The primary amine reacts through dehydration, while the secondary amine reacts through the formation of a carbon-carbon double bond</p> Signup and view all the answers

    What is the purpose of using enamines in organic synthesis?

    <p>To alkylate carbonyl compounds</p> Signup and view all the answers

    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.

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