Question

which of the following carbonyls have a stretching frequency around 1715 cm⁻¹? caution: more than one answer is possible. none of these

Explanation:

Step1: Recall carbonyl stretching frequencies

Carbon - chlorine (C - Cl) groups in acyl chlorides shift the carbonyl stretching frequency to a higher value (around 1770 - 1815 cm⁻¹). Aldehydes have a carbonyl stretching frequency around 1720 - 1740 cm⁻¹, and ketones have a carbonyl stretching frequency around 1710 - 1720 cm⁻¹.

Step2: Analyze each option

The first structure is an acyl chloride (R - CO - Cl), which has a higher - than - 1715 cm⁻¹ carbonyl stretching frequency. The second option "none of these" is incorrect as there are valid options. The third structure is an aldehyde (R - CHO), which has a carbonyl stretching frequency close to 1720 - 1740 cm⁻¹. The fourth structure is a ketone (R - CO - R'), which has a carbonyl stretching frequency around 1710 - 1720 cm⁻¹.

Answer:

The aldehyde and the ketone options have carbonyl stretching frequencies around 1715 cm⁻¹. So the correct answers are the aldehyde - containing option and the ketone - containing option.