Which one of the following is not a straight chain hydrocarbon?

Options

A. `CH_3 - CH_2 -CH_2 - CH_2 - CH_2 - CH_3`
B. `undersetoverset(|)(CH_3)(C)H_3 - CH_2 -CH_2 - CH_2 - undersetoverset(|)(CH_3)(C)H_2`
C. `undersetoverset(|)(CH_3)(C)H_2- CH_2 - CH_2 - CH_2 - CH_2`
D.

Answer

To determine which of the following hydrocarbons is not a straight-chain hydrocarbon, we need to analyze each option based on their structural formulas.

1. **Option 1: CH3-CH2-CH2-CH2-CH2-CH3**
- This structure consists of 6 carbon atoms connected in a linear fashion.
- Therefore, it is a straight-chain hydrocarbon.

2. **Option 2: CH3-CH2-CH2-CH2-CH2-CH3**
- This structure also consists of 6 carbon atoms connected in a linear fashion.
- Hence, it is also a straight-chain hydrocarbon.

3. **Option 3: CH3-CH2-CH2-CH2-CH3**
- This structure has 5 carbon atoms connected in a linear fashion.
- Thus, it is a straight-chain hydrocarbon as well.

4. **Option 4: CH3-CH(CH3)-CH2-CH2-CH2-CH3**
- In this structure, we have a branching at the second carbon (the CH group has a methyl group attached).
- This indicates that it is not a straight-chain hydrocarbon because of the presence of a branch.

Based on the analysis, **Option 4** is the correct answer as it is not a straight-chain hydrocarbon.

### Summary of Steps:
1. Analyze each hydrocarbon structure.
2. Count the number of carbon atoms and check for linearity.
3. Identify any branching in the structure.
4. Conclude which option is not a straight-chain hydrocarbon.