Question

Arrange the following alkenes in decreasing order of their reactivity towards $HBr$ :

• A. I > II > III
• B. II > III > I
• C. III > II > I
• D. III > I > II

Answer 1

Answer: (C)

III > II > I

The reactivity depends upon the stability of the carbocation formed by addition of $H^{+}$. The carbocations resulting from alkenes (I,II, and III) are respectively.

Since the stability decreases in the order: Z > Y > X,

therefore, reactivity decreases in the order : III > II >I.