Which of the following does not exist as geometric isomers ?

Options

A. 3-bromo-2-methyl-2-butene
B. cyclodecene
C. 3-bromo-1-Chloro-1-pentene
D. 3-methyl-2-pentene

Answer

To determine which of the given compounds does not exist as geometric isomers, we need to analyze each option based on the presence of a double bond and the arrangement of substituents around that bond.

### Step-by-Step Solution:

1. **Understanding Geometric Isomerism**:
Geometric isomerism (cis-trans isomerism) occurs in compounds that have restricted rotation around a double bond (C=C) or in cyclic structures. For geometric isomers to exist, the carbon atoms involved in the double bond must have different substituents.

2. **Analyzing the First Option: 3-bromo-2-methyl-2-pentene**:
- Structure: The double bond is between the second and third carbon atoms.
- Substituents: The second carbon has a methyl group (CH₃) and a bromine atom (Br), while the third carbon has two hydrogen atoms (H).
- Symmetry: Since the third carbon has two identical hydrogen atoms, this compound is symmetrical and does not have geometric isomers.

3. **Analyzing the Second Option: Cyclic Decene**:
- Structure: This is a cyclic compound with a double bond.
- Substituents: The cyclic structure allows for different arrangements of substituents around the double bond.
- Conclusion: This compound can exhibit geometric isomerism.

4. **Analyzing the Third Option: 3-bromo-1-chloro-1-pentene**:
- Structure: The double bond is between the first and second carbon atoms.
- Substituents: The first carbon has a bromine atom (Br) and a chlorine atom (Cl), while the second carbon has two hydrogen atoms (H).
- Conclusion: This compound is asymmetrical and can exhibit geometric isomerism.

5. **Analyzing the Fourth Option: 3-methyl-2-pentene**:
- Structure: The double bond is between the second and third carbon atoms.
- Substituents: The second carbon has a methyl group (CH₃) and a hydrogen atom (H), while the third carbon has a methyl group (CH₃) and a hydrogen atom (H).
- Conclusion: This compound is asymmetrical and can exhibit geometric isomerism.

### Final Answer:
The compound that does not exist as geometric isomers is **3-bromo-2-methyl-2-pentene**.