Question

Predict the structural formula of the major product of the reaction of \(2,2,3\)-trimethyloxirane with each set of reagents. (a) \(\mathrm{MeOH} / \mathrm{MeO}^{-} \mathrm{Na}^{+}\) (b) \(\mathrm{MeOH} / \mathrm{H}^{+}\) (c) \(\mathrm{Me}_{2} \mathrm{NH}\)

Short answer

Question: Predict the structural formula of the major product of the reaction of 2,2,3-trimethyloxirane with each set of reagents: (a) MeOH / MeO⁻ Na⁺, (b) MeOH / H⁺, and (c) Me₂NH.

Step-by-step solution

Identify the nucleophile

In this reaction, methoxide ion (MeO⁻) is the nucleophile and will attack the oxirane ring.

Assess the mode of attack

Since methoxide ion is a strong nucleophile, it will preferentially attack the less substituted carbon atom in the oxirane ring.

Predict the intermediate

After the nucleophilic attack on the less substituted carbon atom, the oxirane ring opens, and a new bond is formed between the attacked carbon atom and the methoxide ion. The intermediate now has an ethoxide ion connected to the remaining carbon of the former oxirane ring.

Predict the final product

Finally, the intermediate can be converted to the final product by protonation of the ethoxide ion from methanol solvent, forming the corresponding alcohol. The major product is 3-methoxy-2,2-dimethylbutan-1-ol. (b) Reaction with MeOH / H⁺

Identify the nucleophile

In this reaction, methanol (MeOH) is the nucleophile and reacts under acidic conditions.

Assess the mode of attack

Since methanol is a weak nucleophile, it will preferentially attack the more substituted carbon atom in the oxirane ring.

Predict the intermediate

After the nucleophilic attack on the more substituted carbon atom, the oxirane ring opens, and a new bond is formed between the attacked carbon atom and the methanol. The intermediate has a methanol molecule connected to the remaining carbon of the former oxirane ring.

Predict the final product

The intermediate can lose a proton to become neutral to give the final product. The major product is 1-ethyl-2-methoxypropane. (c) Reaction with Me₂NH

Identify the nucleophile

In this reaction, dimethylamine (Me₂NH) is the nucleophile and will attack the oxirane ring.

Assess the mode of attack

Dimethylamine is an unhindered nucleophile and will preferentially attack the less substituted carbon atom in the oxirane ring.

Predict the intermediate

After the nucleophilic attack on the less substituted carbon atom, the oxirane ring opens, and a new bond is formed between the attacked carbon atom and the dimethylamine. A proton transfer occurs, resulting in a neutral intermediate.

Predict the final product

The major product of this reaction is 1-(dimethylamino)-3,3-dimethylbutan-2-ol.