Which reaction intermediate is formed when Br2/CCl4 reacts with cyclohexene?
Select one:
a. I
b. V
c. II
d. III
e. IV
The Correct Answer and Explanation is :
When cyclohexene reacts with bromine (Br₂) in carbon tetrachloride (CCl₄), the reaction proceeds via an electrophilic addition mechanism, leading to the formation of a bromonium ion intermediate.his three-membered ring structure consists of a positively charged bromine atom bonded to two adjacent carbon atoms that were originally part of the double bond in cyclohexene.
Mechanism Overview:
- Electrophilic Attack: he Br₂ molecule approaches the electron-rich double bond of cyclohexene.he π-electrons of the double bond attack one of the bromine atoms, leading to the formation of a bromonium ion—a three-membered ring with a positive charge on the bromine atom.
- Nucleophilic Attack: he bromide ion (Br⁻), generated during the initial step, attacks the more substituted carbon of the bromonium ion from the opposite side (backside attack).his backside attack results in the opening of the three-membered ring and the formation of a vicinal dibromide product.
he use of CCl₄ as a solvent is significant because it is inert and does not participate in the reaction.his choice of solvent helps distinguish the reaction from those conducted in polar solvents like water or alcohols, where the solvent can act as a nucleophile, leading to the formation of a halohydrin instead of a dibromide.citeturn0search2
he stereochemistry of the addition is anti, meaning the two bromine atoms add to opposite faces of the cyclohexene ring.his anti addition is a characteristic feature of the bromonium ion mechanism.citeturn0search8
n summary, the reaction of Br₂ with cyclohexene in CCl₄ forms a bromonium ion intermediate, which then undergoes nucleophilic attack by a bromide ion to yield a vicinal dibromide product.his mechanism is typical of halogenation reactions of alkenes and is facilitated by the use of an inert solvent like CCl₄.