Which of the following is not an aliphatic compound?

Options

A. Alkane
B. Alkene
C. Alkyne
D. Benzene

Explanation

To determine which of the following is not an aliphatic compound, we need to understand the classification of hydrocarbons. Here’s a step-by-step solution:

### Step 1: Understand Hydrocarbon Classification
Hydrocarbons can be classified into two main categories:
1. **Aliphatic Compounds**: These are open-chain hydrocarbons and can be further divided into:
- **Alkanes** (single bonds)
- **Alkenes** (at least one double bond)
- **Alkynes** (at least one triple bond)

2. **Aromatic Compounds**: These are closed-chain hydrocarbons that contain alternating double bonds and follow Huckel's rule.

### Step 2: Analyze the Options
Now, let’s analyze the options given in the question:
- **Alkane**: This is an open-chain hydrocarbon (e.g., CnH2n+2), so it is aliphatic.
- **Alkene**: This is also an open-chain hydrocarbon (e.g., CnH2n), so it is aliphatic.
- **Alkyne**: This is another open-chain hydrocarbon (e.g., CnH2n-2), so it is aliphatic.
- **Benzene**: This is a closed-chain hydrocarbon (C6H6) with alternating double bonds, making it an aromatic compound.

### Step 3: Identify the Non-Aliphatic Compound
From the analysis:
- Alkane, Alkene, and Alkyne are all aliphatic compounds.
- Benzene is a closed-chain compound and is classified as an aromatic compound.

### Conclusion
Therefore, the compound that is **not an aliphatic compound** is **Benzene**.

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