When placed correctly, substituents can transmit electronic information through the benzene ring. This concept can be discovered and applied using infrared spectroscopy. Explain the carbonyl stretching frequencies for 4-chloroacetophenone and 4-fluoroacetophenone.

• A. The carbonyl stretching frequency of 4-fluoroacetophenone is higher due to increase in single bond character because of extended conjugation.
• B. The carbonyl stretching frequency of 4-chloroacetophenone is smaller due to increase in single bond character because of extended conjugation.
• C. The carbonyl stretching frequency of 4-fluoroacetophenone is higher due to stronger -I effect of F.
• D. The carbonyl stretching frequency of 4-chloroacetophenone is smaller due to stronger -I effect of Cl.

Answer: (C)