Which of the following alkenes is least reactive towards anionic polymerisation ?

Options

A. a. `CH_(2)=CHCH_(3) `
B. b. `CH_(2)=CF_(2)`
C. c. `CH_(2)=CHCN`
D. d. `CH_(2)=CHC_(6)H_(5)`

Explanation

To determine which of the given alkenes is least reactive towards anionic polymerization, we need to analyze the structure of each alkene and the effects of the substituents on the stability of the negative charge that forms during the polymerization process.

### Step-by-Step Solution:

1. **Identify the Alkenes**: The options given are:
- A) CH2=CH-CH3 (Propene)
- B) CH2=CH2 (Ethylene)
- C) CH2=CH-CN (Acrylonitrile)
- D) CH2=CH-C6H5 (Styrene)

2. **Understand Anionic Polymerization**: Anionic polymerization involves the formation of a carbanion (a negatively charged carbon species) when the double bond of the alkene is broken. The stability of this carbanion is crucial for the reactivity of the alkene.

3. **Analyze Each Alkene**:
- **Option A (Propene)**: When the double bond breaks, a CH3 group is attached to the carbanion. The CH3 group has a +I (inductive) effect, which destabilizes the negative charge.
- **Option B (Ethylene)**: Upon breaking, there is no substituent to stabilize the negative charge. Ethylene is relatively stable but does not have any strong stabilizing groups.
- **Option C (Acrylonitrile)**: The CN group has a strong -I (inductive) effect and can stabilize the negative charge effectively, making it more reactive.
- **Option D (Styrene)**: The C6H5 (phenyl) group can stabilize the negative charge through resonance, making it more reactive than propene.

4. **Determine the Least Reactive Alkene**:
- Among the four options, Propene (Option A) is the least reactive towards anionic polymerization because the +I effect of the CH3 group destabilizes the negative charge formed during the polymerization process.

### Conclusion:
The alkene that is least reactive towards anionic polymerization is **A) CH2=CH-CH3 (Propene)**.

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