Which is expected to react most readily with bromine

Options

A. a. `CH_(3)-CH=CH_(2)`
B. b.`CH-=CH`
C. c. `CH_(2)=CH_(2)`
D. d. `CH_(3)CH_(2)CH_(3)`

Explanation

To determine which compound reacts most readily with bromine, we need to analyze the reactivity of alkanes, alkenes, and alkynes with bromine.

### Step-by-Step Solution:

1. **Identify the Types of Compounds**:
- We have three types of hydrocarbons: alkanes, alkenes, and alkynes.
- Alkanes are saturated hydrocarbons (single bonds), alkenes have at least one double bond, and alkynes have at least one triple bond.

2. **Understand the Reactivity with Bromine**:
- Bromine (Br2) can react with alkenes and alkynes through an addition reaction, while alkanes typically require more vigorous conditions (like UV light) to react with bromine.
- The order of reactivity with bromine is generally: **Alkenes > Alkynes > Alkanes**.

3. **Stability of Intermediates**:
- When alkenes react with bromine, they form a more stable carbocation intermediate (allylic carbocation).
- Alkynes can also form a carbocation, but it is less stable than that formed from alkenes (vinylic carbocation).
- Alkanes do not form stable intermediates under normal conditions when reacting with bromine.

4. **Consider Substituents**:
- The presence of electron-donating groups (like -CH3) on alkenes increases their reactivity because they stabilize the positive charge in the carbocation intermediate.
- Therefore, a more substituted alkene (with more electron-donating groups) will react more readily with bromine.

5. **Evaluate the Given Options**:
- Among the options, we need to identify which one is a more substituted alkene.
- If option A represents a more substituted alkene compared to option C, then option A will react more readily with bromine.

6. **Conclusion**:
- Based on the analysis, the compound that is expected to react most readily with bromine is **option A**, which is a more substituted alkene.

### Final Answer:
**Option A** (the more substituted alkene) is expected to react most readily with bromine.