Carbonyl Attack Nucleophilic Addition to Carbonyl Quiz

The oxygen atom is more electronegative than carbon, pulling electron density away and creating a dipole. This leaves the carbon atom with a partial positive charge (electrophilic), making it the perfect target for nucleophiles.

The carbonyl carbon starts as sp2 (trigonal planar). When the nucleophile attacks and forms a new single bond, the carbon transitions to sp3 hybridization, resulting in a tetrahedral intermediate.

As the nucleophile bonds to the carbon, the pi bond breaks and the electron pair shifts entirely onto the oxygen atom, giving it a negative charge and forming an alkoxide ion.

Aldehydes have less steric hindrance (only one alkyl group) and less electronic stabilization (only one electron-donating group), making the carbonyl carbon more "exposed" and more positive than in ketones.

The cyanide ion attacks the carbon, and the oxygen is subsequently protonated. The resulting molecule contains both a hydroxyl (-OH) and a cyano (-CN) group on the same carbon, which is called a cyanohydrin.

Because a ketone already has two alkyl groups attached to the carbonyl carbon, adding a third group from the Grignard reagent results in a carbon bonded to three alkyl groups—a tertiary alcohol.

Acids protonate the carbonyl oxygen, which increases the partial positive charge on the carbon atom. This makes the carbon even more electrophilic and easier for weak nucleophiles to attack.

The transition from sp2 to sp3 hybridization forces the bond angles from 120° to approximately 109.5°, changing the molecular shape from a flat plane to a three-dimensional tetrahedron.

A hemiacetal contains one ether group and one hydroxyl group on the same carbon. If the reaction continues with a second equivalent of alcohol, it becomes a full acetal.

The bisulfite ion (HSO3-) acts as the nucleophile, attacking the electrophilic carbonyl carbon. This reaction is often used for the purification of aldehydes because the product is a water-soluble crystalline solid.

Electron-withdrawing groups pull electron density away from the carbonyl carbon via the inductive effect, making it more positively charged and thus more attractive to an incoming nucleophile.

These reactions are often called addition-elimination because the nucleophile adds to the carbon, but the intermediate then loses a molecule of water to form a double bond between carbon and nitrogen.

Large alkyl groups physically block the nucleophile (steric hindrance), and their ability to donate electron density (inductive effect) reduces the partial positive charge on the carbonyl carbon.

Hemiacetals form when alcohols add to carbonyls; bisulfite adds to form crystalline solids; and Grignard reagents add alkyl groups. Dehydrohalogenation is an elimination reaction, not an addition.

In base-catalyzed reactions, the nucleophile is usually strong enough to attack the neutral carbonyl carbon directly without the need for the oxygen to be protonated first.