Question. Predict the major products of the following reactions, including stereochemistry where appropriate.

1. 2,2-dimethyloxirane +(oxygen-labelled water)
2. 2,2-dimethyloxirane +
3. (2S,3R)-2-ethyl-2,3-dimethyloxirane +

(2S,3R)-2-ethyl-2,3-dimethyloxirane +

In part (a), ring opening of epoxide under acidic conditions takes place in such a way that, in first step, the oxygen of epoxide gets protonated and acquires positive charge, then water attacks as a nucleophile on more hindered carbon of the epoxide so that epoxide ring can open up, which on further hydrolysis leads to formation of the product. Here, oxygen of water is isotopically labelled.

In part (b), ring opening of epoxide under basic conditions takes place in such a way that, the attack of nucleophile occurs at less hindered carbon of the epoxide. Here, oxygen of the nucleophile which is hydroxide ion is isotopically labelled.

Formation of products under acidic and basic conditions

In part (c), ring opening of epoxide under basic conditions takes place in such a way that, the attack of nucleophile, that is methoxide ion occurs at less hindered carbon of the epoxide which leads to opening up of epoxide and further on hydrolysis, we get the required product.

In part (d), ring opening of epoxide under acidic conditions takes place in such a way that, in first step, the oxygen of epoxide gets protonated and acquires positive charge, then methanol attacks as a nucleophile on more hindered carbon of the epoxide so that epoxide ring can open up, which on further hydrolysis leads to formation of the product

Product formation via ring opening of epoxide under acidic and basic conditions