Question

The most stable canonical structure among the given structure is :

• A. I
• B. II
• C. III
• D. all are equally stable

Answer 1

Answer: (A)

I

A resonance structure in which a positive charge is present on the most electronegative atom is highly unstable. Since (III) has a positive charge on the oxygen atom, which has a higher electronegativity than carbon, it is unstable when compared to (I) and (II).

In case of (II), the $-I$ effect of the oxygen atom is higher since it is near the carbocation when compared to (I). Since higher the $-I$ effect, higher the instability of the carbocation, (I) is the most stable resonating structure among the given canonical structures due to alternate loan pair, and double bond which stabilizes the carbocation by resonance.

Hence A is the correct answer