Dehydrohalogenation of an alkyl halide is:

Options

A. An addition reaction
B. A substitution reaction
C. A elimination reaction
D. An oxidation reaction

Answer

**Step-by-Step Solution:**

1. **Understanding Dehydrohalogenation:**
Dehydrohalogenation is a chemical reaction that involves the removal of a hydrogen atom and a halogen atom from an alkyl halide. This results in the formation of an alkene.

2. **Example of Alkyl Halide:**
Consider the alkyl halide 2-bromopropane (CH3-CHBr-CH3). In this compound, bromine (Br) is attached to the second carbon of a three-carbon chain.

3. **Reaction Conditions:**
The reaction typically occurs in a basic medium, such as sodium hydroxide (NaOH).

4. **Reaction Process:**
When 2-bromopropane reacts with NaOH, the hydroxide ion (OH-) acts as a base and abstracts a hydrogen atom from the carbon adjacent to the carbon bonded to bromine.

5. **Formation of the Transition State:**
As the hydroxide ion removes the hydrogen atom, a transition state is formed where the bond between the carbon and the hydrogen is breaking, and the bond between the carbon and bromine is also breaking.

6. **Final Product Formation:**
After the elimination of HBr (which consists of the removed hydrogen and bromine), a double bond forms between the two carbon atoms, resulting in the formation of propene (CH3-CH=CH2).

7. **Type of Reaction:**
This reaction is classified as an elimination reaction, specifically an E2 elimination mechanism, where the elimination occurs in a single concerted step.

**Final Answer:**
Dehydrohalogenation of an alkyl halide is an elimination reaction that results in the formation of an alkene by removing a hydrogen atom and a halogen atom from the alkyl halide.

---