- Introduction to Reactivity of Carbonyl Group
- The carbonyl group (C=O) is a highly reactive functional group found in aldehydes and ketones.
- Understanding the reactivity of the carbonyl group is crucial in organic chemistry.
- The reactivity of carbonyl compounds can be influenced by various factors.
- Nucleophilic Addition Reactions
- Nucleophiles are electron-rich species that can attack and form a covalent bond with the carbonyl carbon.
- Addition reactions occur when a nucleophile adds to the carbonyl group, resulting in the formation of a new compound.
- Examples of nucleophilic addition reactions include:
- Addition of water (hydration)
- Addition of alcohols
- Addition of amines
- Hydration of Carbonyl Compounds
- Aldehydes and ketones can undergo hydration in the presence of water and an acid catalyst.
- The carbonyl group is converted into a geminal diol, or hydrate.
- The reaction is reversible and can be influenced by the reaction conditions.
- Addition of Alcohols (Hemiacetals and Acetals)
- Aldehydes and ketones can react with alcohols to form hemiacetals and acetals.
- Hemiacetals are formed when one alcohol molecule adds to the carbonyl group, resulting in the formation of a new alcohol functional group.
- Acetals are formed when two alcohol molecules add to the carbonyl group.
- The reaction is reversible and can be influenced by the reaction conditions.
- Addition of Amines (Imine and Enamine Formation)
- Aldehydes and ketones can react with primary amines to form imines.
- Imines are formed when the amino group adds to the carbonyl group.
- Secondary amines can react with ketones to form enamines.
- The reaction is reversible and can be influenced by the reaction conditions.
- Oxidation Reactions of Carbonyl Compounds
- Aldehydes can be further oxidized to carboxylic acids.
- The oxidation can be accomplished using mild oxidizing agents such as Tollens’ reagent or Fehling’s solution.
- The reaction involves the conversion of the aldehyde into a carboxylate ion.
- Ketones, on the other hand, are resistant to oxidation under normal conditions.
- Reduction Reactions of Carbonyl Compounds
- Carbonyl compounds can be reduced to alcohols using reducing agents such as sodium borohydride (NaBH4) or lithium aluminum hydride (LiAlH4).
- The reduction process involves the addition of hydrogen atoms to the carbonyl carbon, resulting in the formation of an alcohol functional group.
- Reactivity of Aldehydes and Ketones towards Nucleophiles
- Aldehydes are generally more reactive than ketones towards nucleophilic addition reactions.
- This is because aldehydes have a less sterically hindered carbonyl group compared to ketones.
- Additionally, the electron-withdrawing effect of alkyl groups in ketones makes them less reactive.
- Reactivity of Aldehydes and Ketones towards Strong Nucleophiles
- Aldehydes and ketones can react with strong nucleophiles like Grignard reagents (RMgX) or organolithium compounds (RLi).
- The addition of the nucleophile to the carbonyl group forms a new carbon-carbon bond.
- The reaction proceeds through the formation of a highly reactive alkoxide ion intermediate.
- Reactivity of Aldehydes and Ketones towards Oxidizing Agents
- Aldehydes and ketones can react with oxidizing agents like chromic acid (H2CrO4) or potassium permanganate (KMnO4).
- The reaction results in the oxidation of the carbonyl compound to a carboxylic acid.
- Aldehydes are easily oxidized, while ketones require stronger oxidizing conditions.
- Reactivity of Aldehydes and Ketones towards Reduction
- Aldehydes and ketones can be reduced to alcohols using various reducing agents.
- Sodium borohydride (NaBH4) is commonly used as a mild reducing agent for this purpose.
- The reaction mechanism involves the transfer of a hydride ion (H-) to the carbonyl carbon, resulting in the formation of an alcohol.
- Example:
- Reduction of acetone (a ketone) with NaBH4 yields isopropyl alcohol.
- Reactivity of Aldehydes and Ketones towards Grignard Reagents
- Aldehydes and ketones can react with Grignard reagents (RMgX) to form alcohols.
- The reaction involves the addition of the nucleophilic carbon of the Grignard reagent to the carbonyl carbon.
- The resulting alkoxide ion (RO-) is converted to an alcohol after acidic work-up.
- Example:
- Reaction of propanal (an aldehyde) with methylmagnesium bromide (CH3MgBr) yields 2-methylpropan-2-ol.
- Reactivity of Aldehydes and Ketones towards Cyanide Ion
- Aldehydes and ketones can react with cyanide ion (CN-) to form cyanohydrins.
- The nucleophilic addition of CN- to the carbonyl carbon followed by protonation yields the product.
- Cyanohydrins are important intermediates in organic synthesis.
- Example:
- Reaction of propanal with sodium cyanide (NaCN) yields 2-hydroxypropanenitrile.
- Reactivity of Aldehydes and Ketones towards Wolff-Kishner Reduction
- Aldehydes and ketones can undergo Wolff-Kishner reduction to form alkanes.
- The reaction involves the conversion of the carbonyl group to a methylene group (-CH2-) using hydrazine (H2NNH2) and a strong base.
- The resulting hydrazone is then thermally decomposed to yield the alkane.
- Example:
- Reduction of acetophenone using Wolff-Kishner conditions gives ethylbenzene.
- Reactivity of Aldehydes and Ketones towards Clemmensen Reduction
- Aldehydes and ketones can undergo Clemmensen reduction to form alkanes.
- The Clemmensen reduction involves the reduction of the carbonyl group to a methylene group using amalgamated zinc (Zn(Hg)) and hydrochloric acid (HCl).
- The reaction proceeds through the formation of an organozinc intermediate, followed by elimination of the carbonyl oxygen.
- Example:
- Reduction of benzaldehyde using Clemmensen conditions gives toluene.
- Reactivity of Aldehydes and Ketones towards Nitrogen Compounds
- Aldehydes and ketones can react with nitrogen compounds to form a variety of products.
- Amines can add to the carbonyl group to form imines or enamines, depending on the nitrogen compound used.
- Hydrazines can react with aldehydes and ketones to form hydrazones.
- Example:
- Reaction of acetone with phenylhydrazine yields phenylhydrazone.
- Reactivity of Aldehydes and Ketones towards Organometallic Compounds
- Aldehydes and ketones can react with organometallic compounds such as Grignard reagents and organolithium compounds.
- The carbon-metal bond in the organometallic compound adds to the carbonyl carbon, resulting in the formation of a new carbon-carbon bond.
- The reaction is widely used in organic synthesis.
- Example:
- Reaction of benzaldehyde with phenylmagnesium bromide (PhMgBr) gives 1-phenylethanol.
- Reactivity of Aldehydes and Ketones towards Ammonia Derivatives
- Aldehydes and ketones can react with ammonia derivatives such as hydroxylamine, semicarbazide, and phenylhydrazine.
- These reactions are used for the identification and characterization of carbonyl compounds.
- Example:
- Reaction of acetone with phenylhydrazine yields 2,4-dinitrophenylhydrazone.
- Reactivity of Aldehydes and Ketones towards Oxidizing Agents
- Aldehydes can be easily oxidized to carboxylic acids using oxidizing agents such as potassium permanganate (KMnO4) or chromic acid (H2CrO4).
- Ketones, on the other hand, are resistant to oxidation under normal conditions.
- Example:
- Oxidation of ethanol (an aldehyde) using KMnO4 yields acetic acid.
- Summary of Reactivity of Carbonyl Group
- Aldehydes and ketones exhibit a wide range of reactivity towards different nucleophiles and oxidizing agents.
- The reactivity can be influenced by factors such as the size of the carbonyl group, the presence of electron-donating or withdrawing groups, and the nature of the nucleophile or oxidizing agent.
- Understanding the reactivity of carbonyl compounds is essential for the synthesis and functionalization of organic molecules.
Problem Solving Session Aldehydes And Ketones - Reactivity of carbonyl group
Slide 21:
- Problem:
- Predict the major product formed when propanal reacts with methanol in the presence of an acid catalyst.
- Solution:
- Propanal reacts with methanol to form a hemiacetal.
- The oxygen of the carbonyl group attacks the hydrogen of the alcohol, and the alcohol oxygen becomes protonated.
- Example:
- CH3CH2CHO + CH3OH → CH3CH(OMe)OH
- Problem:
- Predict the major product formed when butanone reacts with phenylmagnesium bromide.
- Solution:
- Butanone reacts with phenylmagnesium bromide to form a tertiary alcohol.
- The carbon of the phenyl group in the Grignard reagent adds to the carbon of the carbonyl group.
- Example:
- CH3COCH2CH3 + PhMgBr → CH3COCH2CH2Ph
- Problem:
- Predict the major product formed when acetone reacts with hydrogen cyanide.
- Solution:
- Acetone reacts with hydrogen cyanide to form a cyanohydrin.
- The nucleophilic cyanide ion attacks the carbonyl carbon, resulting in the formation of a new carbon-carbon bond.
- Example:
- CH3COCH3 + HCN → CH3CH(OH)CN
- Problem:
- Predict the major product formed when benzaldehyde reacts with phenylhydrazine.
- Solution:
- Benzaldehyde reacts with phenylhydrazine to form a phenylhydrazone.
- The hydrazine nitrogen acts as a nucleophile and attacks the carbonyl carbon.
- Example:
- C6H5CHO + C6H5NHNH2 → C6H5CH=N-NHC6H5
- Problem:
- Predict the major product formed when propanal reacts with NaBH4.
- Solution:
- Propanal reacts with sodium borohydride (NaBH4) to form a primary alcohol.
- The hydride ion (H-) reduces the carbonyl group, resulting in the formation of an alcohol.
- Example:
- CH3CH2CHO + NaBH4 → CH3CH2CH2OH
Slide 22:
- Problem:
- Predict the major product formed when butanone is oxidized using chromic acid (H2CrO4).
- Solution:
- Butanone can be oxidized to butanoic acid using chromic acid (H2CrO4) as an oxidizing agent.
- The carbonyl group is converted into a carboxylic acid.
- Example:
- CH3COCH2CH3 + H2CrO4 → CH3COCH2COOH
- Problem:
- Predict the major product formed when 2-propanol is oxidized using potassium permanganate (KMnO4).
- Solution:
- 2-Propanol can be oxidized to acetone using potassium permanganate (KMnO4) as an oxidizing agent.
- The primary alcohol is converted into a ketone.
- Example:
- CH3CH(OH)CH3 + KMnO4 → CH3COCH3
- Problem:
- Predict the major product formed when benzaldehyde is reduced using sodium borohydride (NaBH4).
- Solution:
- Benzaldehyde can be reduced to benzyl alcohol using sodium borohydride (NaBH4) as a reducing agent.
- The carbonyl group is reduced to an alcohol.
- Example:
- C6H5CHO + NaBH4 → C6H5CH2OH
- Problem:
- Predict the major product formed when butanone is reduced using lithium aluminum hydride (LiAlH4).
- Solution:
- Butanone can be reduced to 2-butanol using lithium aluminum hydride (LiAlH4) as a reducing agent.
- The carbonyl group is reduced to an alcohol.
- Example:
- CH3COCH2CH3 + LiAlH4 → CH3CH(OH)CH2CH3
- Problem:
- Predict the major product formed when acetone reacts with methylmagnesium bromide.
- Solution:
- Acetone reacts with methylmagnesium bromide (CH3MgBr) to form 2-methylpropan-2-ol.
- The methyl group of the Grignard reagent adds to the carbonyl carbon.
- Example:
- CH3COCH3 + CH3MgBr → (CH3)2C(OH)CH3
Slide 23:
- Problem:
- Predict the major product formed when propanal is reacted with semicarbazide in the presence of an acid catalyst.
- Solution:
- Propanal reacts with semicarbazide to form a semicarbazone.
- The -NH2 group of the semicarbazide acts as a nucleophile and attacks the carbonyl carbon.
- Example:
- CH3CH2CHO + H2NNHC(O)NH2 → CH3CH2CH=N-NHCONH2
- Problem:
- Predict the major product formed when benzaldehyde is reacted with hydrazine in the presence of an acid catalyst.
- Solution:
- Benzaldehyde reacts with hydrazine to form a phenylhydrazone.
- The -NH2 group of the hydrazine acts as a nucleophile and attacks the carbonyl carbon.
- Example:
- C6H5CHO + H2NNH2 → C6H5CH=N-NH2
- Problem:
- Predict the major product formed when propanal is reacted with Grignard reagent (CH3CH2MgBr).
- Solution:
- Propanal reacts with the Grignard reagent (CH3CH2MgBr) to form 3-hexanol.
- The carbon of the Grignard reagent adds to the carbonyl carbon.
- Example:
- CH3CH2CHO + CH3CH2MgBr → CH3(CH2)3OH
- Problem:
- Predict the major product formed when butanone is reacted with lithium diisopropylamide (LDA).
- Solution:
- Butanone reacts with lithium diisopropylamide (LDA) to form an enolate ion.
- The deprotonated LDA attacks the carbonyl carbon, leading to enol formation followed by tautomeric shift.
- Example:
- CH3COCH2CH3 + LDA → CH3COCH=C(CH3)2
- Problem:
- Predict the major product formed when acetone is reacted with nitrous acid (HNO2).
- Solution:
- Acetone reacts with nitrous acid (HNO2) to form an oxime.
- The -OH group of the nitrous acid acts as a nucleophile and attacks the carbonyl carbon.
- Example:
- CH3COCH3 + HNO2 → CH3C(NOH)CH3
Slide 24:
- Problem:
- Predict the major product formed when propanal reacts with methylamine.
- Solution:
- Propanal reacts with methylamine to form an imine.
- The -NH2 group of methylamine acts as a nucleophile and attacks the carbonyl carbon.
- Example:
- CH3CH2CHO + CH3NH2 → CH3CH2CH=NCH3
- Problem:
- Predict the major product formed when butanone reacts with ethylamine.
- Solution:
- Butanone reacts with ethylamine to form an imine.
- The -NH2 group of ethylamine acts as a nucleophile and attacks the carbonyl carbon.
- Example:
- CH3COCH2CH3 + C2H5NH2 → CH3COCH2CH=NH2
- Problem:
- Predict the major product formed when acetone reacts with ethylene glycol in the presence of an acid catalyst.
- Solution:
- Acetone reacts with ethylene glycol to form a ketal.
- The oxygen of the carbonyl group attacks the hydrogen of the alcohol, and the alcohol oxygen becomes protonated.
- Example:
- CH3COCH3 + HOCH2CH2OH →
Introduction to Reactivity of Carbonyl Group The carbonyl group (C=O) is a highly reactive functional group found in aldehydes and ketones. Understanding the reactivity of the carbonyl group is crucial in organic chemistry. The reactivity of carbonyl compounds can be influenced by various factors.