Question

The order of decreasing ease of abstraction of hydrogen atoms in the following molecule:

• A. $H_a>H_b>H_c$
• B. $H_a>H_c>H_b$
• C. $H_b>H_a>H_c$
• D. $H_c>H_b>H_a$

Answer 1

The correct option is B $H_a>H_c>H_b$

Abstraction of $\left(H_a\right)$ hydrogen atom results in the fomation of $3^{}$ allylic carbocation when abstraction of $H_c$ gives $2^{}$ allylic carbocation (which is less stable as compared to former one. However, abstraction of $H_b$ gives only $2^{}$ carbocation which is less stable as compared to former two. More the stability of general carbocation, higher is the tendency abstraction of hydrogen.
Thus, the order of decreasing ease of abstraction of hydrogen atoms from the given molecule is
$H_a>H_c>H_b$