Aldehydes and Ketones: Short question & answer, mechanism of nucleophilic addition

Aldehydes and Ketones: Short question & answer, mechanism of nucleophilic addition

Question: How is formaldehyde prepared industrially?

Answer.

On industrial scale, formaldehyde is prepared by passing the mixture of methanol vapors and air over iron molybdenum oxides or silver as a catalyst. The reaction is carried out at the temperature of 500 ˚C.

Question: Describe briefly the nucleophile addition mechanism to carbonyl compound.

Answer.

Nucleophilic addition mechanism to carbonyl compound is two types.

i. Base catalyzed Nucleophilic addition reaction

ii. Acid catalyzed Nucleophilic addition reaction

i. Base catalyzed Nucleophilic addition reaction

In the base catalyzed Nucleophilic addition reaction, following steps are involved.

Step 1: Generation of strong nucleophile.

Step 2: Attack of Nucleophile on electrophilic carbon

Step 3: Abstraction of proton and regeneration of base

ii. Acid catalyzed nucleophilic addition reaction

In the acid catalyzed nucleophilic addition reaction, following steps are involved.

Step1: Protonation of carbonyl compound

Step 2: Attack of nucleophile on electrophilic carbon

Question: What is the mechanism of HCN addition to carbonyl compounds?

Answer.

The nucleophilic addition of HCN to carbonyl compound leads to formation of cyanohydrin. This reaction is catalyzed by a base. Following steps are involved during base catalyzed addition of HCN to carbonyl compounds.

Step1: Generation of strong nucleophile.

Step 2: Attack of nucleophile on electrophilic carbon

Step 3: Abstraction of proton and regeneration of base

Question: What is Haloform reaction?

Answer.

The chemical reaction in which haloform (CHX₃) is formed when an aldehyde or ketones containing acetyl group CH₃CO or secondary alcohol containing methyl group and hydroxyl group bonded with same carbon or ethanol reacts with chlorine, bromine, or iodine in the presence of a sodium hydroxide is called haloform reaction.

Question: Which types of alcohols undergo iodoform reaction?

Alcohols that have both methyl group and OH group bonded with same carbon atom undergo iodoform reaction.

r.e.,

Ethanol is the only primary alcohol that gives iodoform reaction.

Question: Why formaldehyde do not give aldol condensation reaction?

Answer:

For a carbonyl compound to undergo aldol condensation reaction, it must have at least one alpha hydrogen( a hydrogen bonded with a carbon directly bonded with carbonyl carbon). Since, formaldehyde has no alpha hydrogen, so it does not afford aldol condensation reaction.

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