Isopropyl bromide when heated with alcoholic KOH gives propene. The reaction is __________.

Options

A. Substitution
B. Elimination
C. Addition
D. cyclisation

Answer

To determine the type of reaction that occurs when isopropyl bromide is heated with alcoholic KOH to produce propene, we can analyze the process step by step.

### Step 1: Identify the Reactants
The reactant in this case is isopropyl bromide, which has the chemical formula \( \text{C}_3\text{H}_7\text{Br} \). It is an alkyl halide.

**Hint:** Look for the structure of isopropyl bromide to understand what functional groups are present.

### Step 2: Understand the Role of Alcoholic KOH
Alcoholic KOH is a strong base. In this reaction, it does not act as a nucleophile but rather as a base that facilitates the elimination of a hydrogen halide (HBr) from the alkyl halide.

**Hint:** Recall the properties of strong bases and how they interact with alkyl halides.

### Step 3: Mechanism of the Reaction
When isopropyl bromide is heated with alcoholic KOH, the hydroxide ion (\( \text{OH}^- \)) from KOH acts as a Bronsted base. It abstracts a hydrogen atom from the carbon adjacent to the carbon bonded to the bromine.

**Hint:** Consider how the base interacts with the hydrogen atoms in the molecule.

### Step 4: Elimination of Bromine
As the base removes a hydrogen atom, the bond between the carbon and the bromine atom becomes unstable. This leads to the elimination of bromine (Br) as bromide ion (\( \text{Br}^- \)).

**Hint:** Think about the concept of elimination reactions where a small molecule (like HBr) is removed from the reactant.

### Step 5: Formation of the Product
The result of this elimination is the formation of a double bond between the two carbon atoms, leading to the formation of propene (\( \text{C}_3\text{H}_6 \)). The overall reaction can be summarized as follows:

\[ \text{C}_3\text{H}_7\text{Br} + \text{KOH} \rightarrow \text{C}_3\text{H}_6 + \text{HBr} + \text{KBr} \]

**Hint:** Visualize the product formation and ensure you account for all atoms involved in the reaction.

### Conclusion
The reaction of isopropyl bromide with alcoholic KOH to produce propene is classified as an **elimination reaction**.

**Final Answer:** The reaction is an **elimination reaction**.