Question

The correct stability order of the following three quinones is

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

Answer 1

Answer: (D)

The keto group has considerable resonance energy; hence more the number of keto groups in a compound, higher is its stability. However, here all the three compounds have same (two) number of keto groups. Compound II is least stable because two adjacent keto groups destabilize the molecule due to positive charge on the adjacent carbon atoms. Relative stability of I and II can be ascertained by the stability of their fully reduced forms (phenols), since, fully reduced form of III has two benzene rings, it will be more stable than the I whose form has only one benzene ring.

Thus