The alkane which has only primary hydrogen atom is

Options

A. pentane
B. iso-pentane
C. neo-pentane
D. 2,2-dimethyl butane

Answer

To determine the alkane that has only primary hydrogen atoms, we need to understand the definitions of primary, secondary, and tertiary carbon atoms and their corresponding hydrogen atoms.

### Step-by-Step Solution:

1. **Understand Primary Hydrogen Atoms**:
- Primary hydrogen atoms are those that are attached to primary carbon atoms. A primary carbon atom is one that is bonded to only one other carbon atom.

2. **Analyze the Given Options**:
- We need to evaluate the structure of each alkane option provided (pentane, isopentane, neopentane, and 2,2-dimethylbutane) to identify the one that contains only primary hydrogen atoms.

3. **Evaluate Pentane**:
- Pentane has the structure: CH3-CH2-CH2-CH2-CH3.
- The terminal carbon atoms (the two CH3 groups) are primary, but the internal carbon atoms (CH2 groups) are secondary. Thus, pentane contains both primary and secondary hydrogen atoms.

4. **Evaluate Isopentane**:
- Isopentane has the structure: CH3-CH(CH3)-CH2-CH3.
- The first and last carbon atoms are primary, but the second carbon is bonded to two other carbon atoms (making it secondary). Therefore, isopentane also has both primary and secondary hydrogen atoms.

5. **Evaluate Neopentane**:
- Neopentane has the structure: C(CH3)4 (a central carbon bonded to four CH3 groups).
- All the carbon atoms in neopentane are primary because each CH3 group is attached to the central carbon atom, which is the only carbon it is bonded to. Thus, all hydrogen atoms in neopentane are primary.

6. **Evaluate 2,2-Dimethylbutane**:
- 2,2-Dimethylbutane has the structure: CH3-C(CH3)2-CH2-CH3.
- The terminal carbon atoms are primary, but the central carbon (C(CH3)2) is bonded to three other carbon atoms, making it tertiary. Thus, this compound contains both primary and tertiary hydrogen atoms.

7. **Conclusion**:
- The only alkane that contains only primary hydrogen atoms is **neopentane**.

### Final Answer:
The alkane which has only primary hydrogen atoms is **neopentane**.

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