Question

which of the following carbonyls have a stretching frequency around 1715 cm⁻¹? caution: more than one answer is possible.

Explanation:

Cyclohexanone and cyclopentanone are simple cyclic ketones. The carbon - oxygen double - bond (C=O) stretching frequency of simple cyclic ketones is around 1715 cm⁻¹. Benzoic acid has a C=O stretching frequency in the range of 1680 - 1720 cm⁻¹ due to conjugation with the benzene ring, but it is also in the vicinity of 1715 cm⁻¹.

Answer:

All of the above (assuming the three structures shown are cyclohexanone, cyclopentanone, and benzoic acid)