Incorret statement about addition of halogen to alkenes

Options

A. It is electrophilic addition
B. Syn addition of halogen to C = C takes place
C. Three membered cyclic halonium ion is intermediate
D. Vicinal dihalides are formed.

Answer

To determine the incorrect statement about the addition of halogens to alkenes, we will analyze the process of halogen addition step-by-step.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- Alkenes are compounds that contain a carbon-carbon double bond (C=C). When halogens (like Br2) are added to alkenes, a chemical reaction occurs.

2. **Electrophilic Addition Mechanism**:
- The addition of halogens to alkenes is classified as an electrophilic addition reaction. In this reaction, the double bond acts as a nucleophile and attacks the electrophilic halogen molecule (Br2).

3. **Formation of Bromonium Ion**:
- When Br2 approaches the alkene, one of the bromine atoms becomes positively charged (δ+) and the other becomes negatively charged (δ-). The alkene double bond attacks the δ+ bromine, leading to the formation of a cyclic intermediate known as a bromonium ion. This intermediate is a three-membered ring structure.

4. **Nucleophilic Attack**:
- After the formation of the bromonium ion, the negatively charged bromine ion (Br-) can attack the more substituted carbon of the bromonium ion. This attack occurs from the opposite side of the bromonium ion, resulting in an anti addition of bromine across the double bond.

5. **Formation of the Product**:
- The final product of this reaction is a vicinal dibromide, where the two bromine atoms are added to adjacent carbon atoms, and they are positioned on opposite sides (anti configuration).

6. **Identifying the Incorrect Statement**:
- Now, we need to identify which statement about this reaction is incorrect. The statements can be summarized as follows:
- A) The addition is electrophilic (Correct)
- B) A three-membered cyclic halonium ion is an intermediate (Correct)
- C) Vicinal dibromide is formed (Correct)
- D) The addition is syn (Incorrect)

- The incorrect statement is that the addition of halogen to carbon-carbon double bonds occurs via syn addition. In reality, the addition is anti due to the mechanism described.

### Conclusion:
The incorrect statement about the addition of halogen to alkenes is that the addition is syn. The correct addition mechanism is anti addition.

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