Question

What would be the product formed when 1−bromo−3−chlorocyclobutane reacts with two equivalents of metallic sodium in the ether?

A . 1-Bromocyclobutane

B . 1 - Chlorocyclobutane

C . Cyclobutane

D . Bicyclo ( 1 , 1 , 0 ) ) butane

Answer 1

Hint: In this question, intramolecular Wurtz reaction is taking place. With the help of radical species R, the Wurtz reaction entails the transfer of halogen and metal in order to create a carbon-carbon bond that results from a nucleophilic substitution process. The process involves reacting alkyl halides with metallic sodium in the presence of dry ether to produce higher alkanes.
Wurtz reaction equation:
R-X + 2Na + X-R→ R–R + 2NaX, where X = halogen (Cl, Br, I)

Complete step by step solution:
Given that 1−bromo−3−chlorocyclobutane reacts with two equivalents of metallic sodium in the ether.
In the first step, Na will attack the Bromine-Carbon bond and a carbanion will be formed on the chlorocyclobutane.

After the formation of carbanion, Na will attack the Chlorine-Carbon bond and another carbanion will be formed on the chlorocyclobutane.

The formation of two carbanions on a 4-membered ring is very unstable and hence the two carbanions join to form a bond, and thus form Bicyclo ( 1 , 1 , 0 ) butane

Hence, the overall chemical reaction when 1−bromo−3−chlorocyclobutane reacts with two equivalents of metallic sodium in the ether is:

Thus, Option (D) is correct.

Note: A BrCl molecule is removed in this intramolecular Wurtz reaction, and a Carbon-Carbon bond is created, producing a bicyclic compound. The order of reactivity of alkyl halides in Wurtz reaction is R-I(alkyl iodide) >R-Br(alkyl bromide) >R-Cl(alkyl chloride), because Carbon-Bromine bond is weaker than Carbon-Chlorine bond. Hence. Wurtz reaction will take place with C-Br bond in the first step.