Which of the following Alkane can not be prepared by
hydrogenation of Olefin

Options

A. (A) Propane
B. (B) butane
C. (C) pentane
D. (D) Neo pentane

Answer

To determine which alkane cannot be prepared by hydrogenation of an olefin, we will analyze each option step by step.

### Step 1: Understand Hydrogenation
Hydrogenation is a chemical reaction where an alkene (olefin) reacts with hydrogen (H2) in the presence of a catalyst to form an alkane. The general reaction can be represented as:
\[ \text{Alkene} + H_2 \rightarrow \text{Alkane} \]

### Step 2: Analyze Each Option
We will go through the options one by one to see if they can be formed by hydrogenation of their respective alkenes.

#### Option A: Propane (C3H8)
1. The alkene corresponding to propane is propene (C3H6), which has the structure CH3-CH=CH2.
2. When propene reacts with hydrogen, it forms propane:
\[ \text{CH}_3\text{-CH}=\text{CH}_2 + H_2 \rightarrow \text{CH}_3\text{-CH}_2\text{-CH}_3 \]
3. Therefore, propane can be prepared by hydrogenation.

#### Option B: Butane (C4H10)
1. The alkene corresponding to butane is butene (C4H8), which can be either 1-butene (CH2=CH-CH2-CH3) or 2-butene (CH3-CH=CH-CH3).
2. Both alkenes can react with hydrogen to form butane:
\[ \text{CH}_2=\text{CH}-\text{CH}_2-\text{CH}_3 + H_2 \rightarrow \text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_3 \]
3. Thus, butane can also be prepared by hydrogenation.

#### Option C: Pentane (C5H12)
1. The alkene corresponding to pentane is pentene (C5H10), which can be 1-pentene (CH2=CH-CH2-CH2-CH3) or 2-pentene (CH3-CH=CH-CH2-CH3).
2. Both alkenes can react with hydrogen to yield pentane:
\[ \text{CH}_2=\text{CH}-\text{CH}_2-\text{CH}_2-\text{CH}_3 + H_2 \rightarrow \text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_3 \]
3. Therefore, pentane can also be prepared by hydrogenation.

#### Option D: Neopentane (C5H12)
1. Neopentane has the structure (CH3)4C, which means it has a central carbon atom bonded to four methyl groups.
2. The corresponding alkene (neopentene) cannot be formed because there is no double bond possible with the central carbon having four substituents.
3. Therefore, neopentane cannot be prepared by hydrogenation of any olefin.

### Conclusion
The alkane that cannot be prepared by hydrogenation of an olefin is **neopentane (Option D)**.

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