Which are not position isomers?

Options

A. `CH_(3)-underset(CH_(3))underset("| ")"CH"-underset(CH_(3))underset("| ")"CH"-CH_(3) and CH_(3)-overset(CH_(3))overset("| ")underset(CH_(3))underset("| ")"C "-CH_(2)-CH_(3)`
B. `CH_(3)-underset(H)underset(|)C-CH_(2)-underset(Cl)underset(|)C=O and CH_(3)-underset(Cl)underset(|)CH-CH_(2)-underset(H)underset(|)C=O`
C.
D.

Answer

To determine which of the given options are not position isomers, we need to first understand the concept of isomers and specifically position isomers.

### Step-by-Step Solution:

1. **Understanding Isomers**:
- Isomers are compounds that have the same molecular formula but different structural formulas. This means they have the same number of each type of atom but are arranged differently.

2. **Identifying Position Isomers**:
- Position isomers are a specific type of isomer where the same functional group is attached to different carbon atoms in the carbon chain. For example, if you have a butane chain and you place a methyl group at different positions, those are position isomers.

3. **Analyzing Option A**:
- The first option presents two structures:
- Structure 1: CH3-CH(CH3)-CH(CH3)-CH3
- Structure 2: CH3-CH(CH3)-CH2-CH3
- Both structures have the same molecular formula but differ in the position of the substituents. Therefore, they are position isomers.

4. **Analyzing Option B**:
- The second option provides:
- Structure 1: CH3-CH(CH3)-CH2-C(Cl)=O
- Structure 2: CH3-CH(Cl)-CH2-C(=O)H
- Here, the first structure has an acyl chloride functional group while the second has an aldehyde functional group. Since they have different functional groups, they are functional isomers, not position isomers.

5. **Analyzing Option C**:
- The third option gives:
- Structure 1: CH3-CH2-CH2-CH2-CH3
- Structure 2: CH3-CH2-CH2-CH3
- The molecular formula for these two structures is different as one has an additional CH2 group. Therefore, they are not isomers at all, and consequently, not position isomers.

6. **Analyzing Option D**:
- The fourth option presents:
- Structure 1: CH3-CH(CH3)-CH2-CH3
- Structure 2: CH3-CH(CH3)-CH(CH3)-CH3
- Both structures have the same functional group and differ in the position of the substituents. Therefore, they are position isomers.

7. **Conclusion**:
- After analyzing all options, we find that options B and C are not position isomers. Option B is a case of functional isomers, and option C does not represent isomers at all due to different molecular formulas.

### Final Answer:
The correct answer is **B and C**.