Chemistry - ALCOHOL & ETHER Question with Solution | TestHub
Due to severe angle strain, epoxides undergo ring opening reactions readily. In the presence of an acid
catalyst, such as sulfuric acid, epoxides are hydrolyzed to glycols. Because there is some carbocation
character developed in the transition state for an acid-catalyzed epoxide ring opening, attack of the
nucleophile on unsymmetrical epoxides occurs preferentially at the carbon better able to bear a partial
positive charge. Epoxides undergo ring-opening reactions with a variety of nucleophiles. Good nucleophiles attack an epoxide ring by an SN2 mechanism and show an SN2 -like regioselectivity; that is, the nucleophile attacks at the less hindered carbon.
The product of the following reaction is
Options:
Answer:
Solution:
Explain Question:
The question asks for the product formed when a substituted epoxide reacts with LiAID4 , followed by
aqueous work-up (H2O), focusing on the position of deuterium (D) and –OH groups.
Concept:
Epoxide Ring Opening, Nucleophilic Attack by Hydride/Deuteride, Regioselectivity, Reduction by
LiAlD4
Solution: Epoxides undergo nucleophilic ring opening with LiAID4 , where D- (deuteride) acts as a strong
nucleophile. Under these basic conditions, the nucleophile attacks the less substituted carbon of the
epoxide via an S<sub>N</sub>2 mechanism. Thus, D attaches to the less substituted carbon, while the
oxygen remains on the more substituted carbon as an alkoxide.
In the second step, treatment with H2O protonates the alkoxide to form an –OH group (not–OD), because
the proton source is ordinary water. Therefore, the final product contains D on the less substituted carbon and –OH on the more substituted carbon.
Final Answer: Option (A)
