Question

Each of the following alkenes undergoes addition reaction with bromine. Under the same reaction conditions, the CORRECT trend in the reaction rates is: 
 

• A. ( {I}>{II}>{III} )
• B. ( {II}>{III}>{I} )
• C. ( {I}>{III}>{II} )
• D. ( {III}>{II}>{I} )

Hint:

For reactions involving electrophiles like bromine, the reactivity of alkenes increases with electron-donating groups and decreases with electron-withdrawing groups.

Answer 1

The Correct Option is B

Step 1: Analyze the effect of substituents on the alkene. The rate of bromine addition to alkenes depends on the electron density in the double bond. Electron-donating groups increase the electron density, making the alkene more reactive towards bromine. Conversely, electron-withdrawing groups reduce the electron density, decreasing the reactivity.
Step 2: Reactivity of each compound. - Compound I: Contains a strongly electron-withdrawing ( -{COOH} ) group. This reduces the electron density in the double bond, making it the least reactive. - Compound II: Contains an electron-donating ( -{CH}_3 ) group, which increases the electron density in the double bond, making it highly reactive. - Compound III: Contains no significant electron-donating or electron-withdrawing groups. Its reactivity lies between that of Compound I and Compound II.
Step 3: Arrange the reactivity. Based on the substituent effects: [ {Rate of reaction: II>III>I}. ] 
Step 4: Conclusion. The correct trend in the reaction rates is ( {II}>{III}>{I} ).