Question

Use resonance arguments to rank the above in order of increasing acidity :

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

Answer 1

The correct option is A $H_c<H_a<H_b$

In the given structure $H_a$ is present next to $C=O$,

$H_b$ is in conjugation with $C=C$ and that extends to $C=O$

$H_c$ has no conjugation.

Therefore $H_b$ is most acidic and $H_c$ is least acidic

Therefore the order of acidity is :

$H_b$>$H_a$>$H_c$

Option A is correct.