Q 11-11-31 E

Question

We saw in Section 8-7 that bromohydrins are converted into epoxides when treated with base. Propose a mechanism, using curved arrows to show the electron flow.

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Answer

The mechanism for the conversion of bromohydrins to epoxides on treating with base is,

1Halohydrin to epoxide

In converting halohydrin to epoxide, the base deprotonates the alcohol and forms an alkoxide intermediate. Further by S_N2 reaction, the nucleophile (alkoxide) attacks the electrophilic C and displaces the leaving group (halide ion).

2The mechanism for the conversion of bromohydrins to epoxides on treating with a base

When a starting material, bromohydrin, is rotated by 180^o, the C-C bonds are rotated so that the –OH and –Br bonds are 180^o apart. Now, bromohydrin is treated with a base, and proton removal occurs.

After that, the S_N2 displacement -Br^-of -O⁺ by occurs, which leads to the formation of epoxide ring and ion. This reaction is an intramolecular S_N2 displacement.

The mechanism for the conversion of bromohydrins to epoxides

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