The number of pi bonds in the molecule below is
A) 1
B) 2
C) 3
D) 5
E) 9

Question

The number of pi bonds in the molecule below is 
A) 1 
B) 2 
C) 3 
D) 5 
E) 9

Quizplus · Accepted Answer

There are 6 double bonds (also known as pi bonds) in the cyclic rings and one additional double bond connecting the nitrogen to the carbonyl group. Therefore, the total number of pi bonds in the molecule is 6 + 1 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 = 7. However, the molecule has a resonance structure where the double bond connecting the nitrogen to the carbonyl group moves to the adjacent carbon-carbon double bond. This resonance structure has 2 additional pi bonds, bringing the total to 9. Another resonance structure can be drawn where the double bond between the two cyclic rings moves to another adjacent carbon-carbon double bond, adding another 2 pi bonds, making it a total of 11. Therefore, the correct answer is C) 3, which reflects the number of resonance structures that contribute to the total number of pi bonds.

The Number of Pi Bonds in the Molecule Below Is