Alkenes react rapidly with bromine in non-nucleophilic solvents to form vicinal dibromides.This reaction can be best described as

Options

A. Electrophilic addition
B. Nucleophilic addition
C. Nucleophilic substitution
D. Electrophilic substitution

Answer

To solve the question regarding the reaction of alkenes with bromine in non-nucleophilic solvents to form vicinal dibromides, we can break down the process step by step.

### Step 1: Identify the Reaction Type
Alkenes react with bromine in non-nucleophilic solvents (like carbon tetrachloride, CCl4) to form vicinal dibromides. This indicates that the reaction involves the addition of bromine across the double bond of the alkene.

**Hint:** Look for the type of reaction that involves the addition of atoms or groups across a double bond.

### Step 2: Mechanism of the Reaction
The reaction proceeds via an electrophilic addition mechanism. In this mechanism, bromine (Br2) acts as an electrophile.

**Hint:** Consider how the double bond in alkenes can act as a nucleophile, attacking electrophiles.

### Step 3: Formation of Bromonium Ion
When bromine approaches the alkene, it undergoes heterolytic fission, resulting in the formation of a bromonium ion. This ion is a three-membered cyclic structure where one bromine atom is positively charged and is bonded to the two carbon atoms of the alkene.

**Hint:** Remember that the formation of a cyclic intermediate is a key feature of electrophilic addition reactions.

### Step 4: Nucleophilic Attack
After the bromonium ion is formed, a bromide ion (Br-) generated from the initial dissociation of Br2 acts as a nucleophile. It attacks one of the carbon atoms in the bromonium ion, leading to the opening of the three-membered ring and forming the vicinal dibromide product.

**Hint:** Think about how nucleophiles interact with positively charged centers in the reaction mechanism.

### Step 5: Resulting Product
The final product of this reaction is a vicinal dibromide, where bromine atoms are added to adjacent carbon atoms (vicinal positions) of the original alkene.

**Hint:** Visualize the structure of the product to confirm the positions of the bromine atoms.

### Final Answer
The reaction of alkenes with bromine in non-nucleophilic solvents to form vicinal dibromides can be best described as an **electrophilic addition reaction**.