Aldehydes and Ketones: Reactions and Mechanisms

Vocabulary concepts covering the electrophilicity, hydration, cyanohydrin formation, and reduction reactions of aldehydes and ketones based on Chapter 19 lecture notes.

1,1-diols (Geminal diols)

The product formed when aldehydes and ketones react with water in a hydration reaction.

Electrophilicity Comparison

Aldehydes are more polarized and more reactive in nucleophilic addition reactions than ketones because ketones have more alkyl groups that inductively stabilize the $C=O$ carbon.

Aromatic Aldehyde Carbonyl Carbon

The carbonyl carbon atom is less positive in an aromatic aldehyde compared to an aliphatic aldehyde.

Base-catalyzed hydration nucleophile

The hydroxide ion ($:OH^-$), which is a better nucleophile than water.

Acid-catalyzed hydration initiator

The hydronium ion ($H_3O^+$), which is generated to facilitate the reaction.

Chloral hydrate

The hydrate form of trichloroacetaldehyde that exists primarily when the compound is dissolved in water.

Cyanohydrin

An adduct formed by the reversible, base-catalyzed nucleophilic addition of $HCN$ to aldehydes and unhindered ketones; the process generates the cyanide ion ($CN^-$) as the nucleophile.

Cyanohydrin Hydrolysis

A process using $H_3O^+$ and heat that converts a cyanohydrin into a carboxylic acid.

Cyanohydrin Reduction

A process using $LiAlH_4$ and $H_2O$ that converts a cyanohydrin into an aminoalcohol.

Steric Hindrance in Cyanohydrin Formation

Cyclohexanone forms cyanohydrins in good yield, but $2,2,6 ext{-trimethylcyclohexanone}$ does not react because it is bulky and hindered.

Aldehyde Reduction with $NaBH_4$

A reaction that converts an aldehyde into a primary ($1^{ ext{o}}$) alcohol.

Ketone Reduction with $NaBH_4$

A reaction that converts a ketone into a secondary ($2^{ ext{o}}$) alcohol.

Aldehyde Grignard Reaction

The addition of a Grignard reagent ($RMgX$) followed by $H_3O^+$ to an aldehyde to produce a secondary ($2^{ ext{o}}$) alcohol.

Ketone Grignard Reaction

The addition of a Grignard reagent ($RMgX$) followed by $H_3O^+$ to a ketone to produce a tertiary ($3^{ ext{o}}$) alcohol.

Nucleophilic Addition of $H-Y$

A readily reversible reaction favored when $Y$ is an electronegative group (such as $OH$, $OCH_3$, $Br$, $Cl$, or $HSO_4^-$) that can stabilize a negative charge.

Grignard Mechanism Electrophilicity

In the mechanism of a Grignard reaction, the carbonyl carbon ($C$) is the electrophilic site attacked by the nucleophilic $R^-$ group.