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)

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 : $III>II>I$.