Organometallic Bonds: Grignard Reagent Addition Quiz

The trigonal planar sp2 carbonyl carbon is attacked by the nucleophile to form a tetrahedral sp3 hybridized magnesium alkoxide intermediate.

The lone pairs on the ether oxygen act as Lewis bases, stabilizing the electron-deficient magnesium center and helping to keep the Grignard reagent in solution.

Formaldehyde gives primary alcohols. All other aldehydes possess one R-group, so adding a second R-group from the Grignard reagent results in a secondary alcohol.

Grignard reagents are extremely strong bases (pKa of alkanes is approx 50). They react instantly with water to abstract a proton, forming the corresponding alkane.

The nucleophilic carbon of the Grignard reagent attacks the empty pi-star antibonding orbital, which has the largest coefficient at the carbon atom.

Any group with an acidic proton (O-H, N-H, S-H, C-O-O-H) will undergo an acid-base reaction with the Grignard reagent, destroying it.

The reaction initially forms a magnesium alkoxide salt. Acidic workup provides the proton necessary to yield the neutral alcohol.

Alcohols contain acidic protons. The Grignard reagent would react with the solvent itself to form an alkane and a magnesium alkoxide, rendering it useless for synthesis.

Benzaldehyde provides the phenyl ring and one carbon; the Grignard adds the second phenyl ring, resulting in a secondary alcohol with two phenyl groups.

[Image comparing steric and inductive effects in aldehydes vs ketones] Ketones have two alkyl groups that sterically block the nucleophile and inductively donate electron density, making the carbonyl carbon less electrophilic.

Formaldehyde has one carbon. Adding a methyl group (one carbon) results in a two-carbon primary alcohol, which is ethanol.

This is one of the most important aspects of Grignard chemistry; it allows for the systematic buildup of the carbon skeleton.

The Felkin-Anh model (and the older Cram Rule) predicts the major product based on the approach of the nucleophile from the least hindered face.

Ethers like diethyl ether and THF are required because they are aprotic (no acidic protons) and can coordinate to the magnesium atom.

Acetaldehyde has two carbons. Adding a methyl group makes three carbons. The oxygen is on the second carbon, creating the secondary alcohol propan-2-ol (isopropanol).