Which of the following cannot show geometrical isomerism

Options

A. `1-`phenylbut`-1-`ene
B. Hex`-2-`ene
C. `1-`Chloroethene
D. `1-`Chloropropene

Explanation

To determine which compound cannot show geometrical isomerism, we will analyze each of the given compounds step by step.

### Step 1: Analyze 1-phenyl-but-1-ene
1. **Structure**: The structure of 1-phenyl-but-1-ene can be represented as:
\[ \text{C}_6\text{H}_6\text{C}=\text{C}\text{H}\text{C}_2\text{H}_5 \]
Here, we have a double bond between the second and third carbon atoms.

2. **Geometrical Isomerism**: For geometrical isomerism to occur, the two carbon atoms involved in the double bond must have different substituents. In this case, the second carbon has a phenyl group and a hydrogen, while the third carbon has a hydrogen and an ethyl group.

3. **Conclusion**: Since the substituents are different, 1-phenyl-but-1-ene can show geometrical isomerism.

### Step 2: Analyze hex-2-ene
1. **Structure**: The structure of hex-2-ene is:
\[ \text{CH}_3\text{CH}_2\text{C}=\text{C}\text{CH}_2\text{CH}_3 \]
The double bond is between the second and third carbon atoms.

2. **Geometrical Isomerism**: The second carbon has a hydrogen and a methyl group, while the third carbon has a hydrogen and an ethyl group. Thus, they have different substituents.

3. **Conclusion**: Hex-2-ene can show geometrical isomerism.

### Step 3: Analyze 1-chloroethene
1. **Structure**: The structure of 1-chloroethene is:
\[ \text{C}=\text{C}(\text{Cl})\text{H} \]
Here, both carbon atoms in the double bond have at least one hydrogen atom attached.

2. **Geometrical Isomerism**: Since both carbon atoms have the same substituent (hydrogen), they cannot form geometrical isomers.

3. **Conclusion**: 1-chloroethene cannot show geometrical isomerism.

### Step 4: Analyze 1-chloropropene
1. **Structure**: The structure of 1-chloropropene is:
\[ \text{C}=\text{C}(\text{Cl})\text{H}\text{CH}_3 \]
The first carbon has a chlorine and a hydrogen, while the second carbon has a hydrogen and a methyl group.

2. **Geometrical Isomerism**: The substituents on the double bond are different, allowing for the possibility of cis and trans forms.

3. **Conclusion**: 1-chloropropene can show geometrical isomerism.

### Final Conclusion
Among the given compounds, **1-chloroethene** is the only compound that cannot show geometrical isomerism.

### Answer
1-chloroethene cannot show geometrical isomerism.

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