Questions: Which of the following carbonyls have a stretching frequency around 1745 cm^-1? Caution: More than one answer is possible. none of these

Solution Steps

• Ester (first structure): Esters typically have a C=O stretching frequency around 1735-1750 cm⁻¹. This falls within the range given in the problem.

• Anhydride: Anhydrides typically have _two_ carbonyl stretching frequencies around 1760 and 1820 cm⁻¹. Neither of these falls within the range given in the problem. The second structure has a conjugated ketone and a strained anhydride, so it would have slightly lower wavenumbers, but still outside the asked for range.

• Lactam (third structure): Amides, including lactams, usually have a C=O stretching frequency around 1650-1690 cm⁻¹. This is significantly lower than the value given in the problem.

The only structure with a carbonyl stretching frequency around 1745 cm⁻¹ is the ester.

Final Answer