The compound having only primary hydrogen atoms is

Options

A. Isobutane
B. 2,3-dimethyl butene
C. Cyclohexane
D. Propyne

Answer

To determine the compound that has only primary hydrogen atoms, we need to understand the definitions of primary hydrogen and primary carbon.

### Step-by-Step Solution:

1. **Define Primary Hydrogen and Primary Carbon**:
- Primary hydrogen atoms are those that are attached to primary carbon atoms.
- Primary carbon atoms are those that are bonded to only one other carbon atom.

2. **Analyze the Given Compounds**:
- We will analyze the structures of the given compounds to identify the type of hydrogen atoms present.

3. **Examine Isobutane**:
- Structure: (CH3)3CH
- In isobutane, we have one carbon that is attached to three other carbons (tertiary carbon), and the remaining hydrogen atoms are attached to primary carbons.
- Conclusion: Isobutane contains tertiary hydrogens, so it does not qualify.

4. **Examine 2,3-Dimethylbutene**:
- Structure: CH3-CH(CH3)-CH(CH3)-CH2
- This compound has both primary and tertiary carbons.
- Conclusion: It contains tertiary hydrogens, so it does not qualify.

5. **Examine Cyclohexane**:
- Structure: A six-membered ring (C6H12).
- All carbons in cyclohexane are secondary (each carbon is bonded to two other carbons).
- Conclusion: Cyclohexane does not have any primary hydrogens.

6. **Examine Propane**:
- Structure: CH≡C-CH3
- Propane has three carbon atoms, all of which are primary carbons.
- Each carbon in propane is attached to only one other carbon, meaning all hydrogen atoms are primary.
- Conclusion: Propane has only primary hydrogen atoms.

7. **Final Answer**:
- The compound that has only primary hydrogen atoms is **Propane**.