The compound having only primary hydrogen atoms is

Options

A. butene
B. iso- butene
C. cyclohexene
D. 2,3-dimethyl butene

Answer

To determine the compound 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. **Understanding Primary Carbons and Hydrogens**:
- A **primary carbon** is a carbon atom that is bonded to only one other carbon atom. It can bond with three hydrogen atoms.
- Therefore, the hydrogen atoms attached to primary carbons are called **primary hydrogen atoms**.

2. **Analyzing the Given Compounds**:
- We will analyze each compound mentioned in the video transcript to identify if they contain only primary hydrogen atoms.

3. **Butene**:
- Structure: CH2=CH-CH2-CH3
- The first carbon (double-bonded) is primary (bonded to one carbon and three hydrogens).
- The terminal carbon is also primary.
- The middle carbons are secondary (bonded to two carbons).
- Conclusion: Contains both primary and secondary hydrogens.

4. **Isobutene**:
- Structure: CH2=C(CH3)-CH3
- The carbon with the double bond is primary (bonded to one carbon).
- The other two carbons are also primary (each bonded to one carbon).
- Conclusion: All hydrogen atoms are primary.

5. **Cyclohexene**:
- Structure: A cyclic structure with six carbon atoms and one double bond.
- Each carbon in cyclohexene is bonded to two other carbons.
- Conclusion: All hydrogen atoms are secondary.

6. **2,3-Dimethylbutene**:
- Structure: CH2=C(CH3)-CH(CH3)-CH3
- The terminal carbon is primary, but the second and third carbons are secondary (bonded to three carbons).
- Conclusion: Contains both primary and secondary hydrogens.

7. **Final Conclusion**:
- The only compound that contains only primary hydrogen atoms is **Isobutene**.

### Final Answer:
The compound having only primary hydrogen atoms is **Isobutene**.