How many structural isomeric alkene possible for molecule formula `C_5H_10` which can show geometrical isomerism ?

Options

A. 1
B. 2
C. 0
D. 3

Answer

To determine how many structural isomeric alkenes are possible for the molecular formula C₅H₁₀ that can show geometrical isomerism, we can follow these steps:

### Step 1: Identify the structural isomers of C₅H₁₀
We start by identifying all possible structural isomers of alkenes with the formula C₅H₁₀. Alkenes contain a carbon-carbon double bond (C=C), and we can have different arrangements of the carbon skeleton.

1. **1-Pentene**: CH₃-CH₂-CH₂-CH=CH₂
2. **2-Pentene**: CH₃-CH₂-CH=CH-CH₃
3. **3-Pentene**: CH₃-CH=CH-CH₂-CH₃
4. **Cyclopentene**: C₅H₁₀ in a cyclic structure
5. **Methylcyclobutene**: A cyclobutane with a methyl group and a double bond.

### Step 2: Check for geometrical isomerism
Next, we need to check which of these structural isomers can exhibit geometrical isomerism (cis-trans isomerism). For geometrical isomerism to occur, the carbon atoms involved in the double bond must have two different substituents.

1. **1-Pentene**: No geometrical isomerism (both ends have identical hydrogen atoms).
2. **2-Pentene**: Yes, it can show geometrical isomerism (cis and trans forms).
- **Cis-2-pentene**: CH₃-CH₂-CH=CH-CH₃ (with CH₃ and H on the same side)
- **Trans-2-pentene**: CH₃-CH₂-CH=CH-CH₃ (with CH₃ and H on opposite sides)
3. **3-Pentene**: No geometrical isomerism (similar reasoning as 1-pentene).
4. **Cyclopentene**: No geometrical isomerism (only one form due to the cyclic structure).
5. **Methylcyclobutene**: No geometrical isomerism (the double bond is in a cyclic structure).

### Step 3: Count the isomers that show geometrical isomerism
From the analysis above, only **2-pentene** shows geometrical isomerism. Therefore, the total number of structural isomeric alkenes for C₅H₁₀ that can show geometrical isomerism is **1** (which is 2-pentene).

### Final Answer
The number of structural isomeric alkenes possible for the molecular formula C₅H₁₀ that can show geometrical isomerism is **1**.

---