Question

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

Explanation:

Step1: Recall carbonyl stretching frequencies

Conjugated aldehydes and ketones have lower - than - normal carbonyl stretching frequencies due to resonance. A carbonyl stretching frequency around 1715 cm⁻¹ is characteristic of a non - conjugated aliphatic aldehyde or ketone.

Step2: Analyze the first compound

The first compound is a conjugated aldehyde. The carbonyl is conjugated with the double bond, and its carbonyl stretching frequency will be lower (around 1690 - 1650 cm⁻¹).

Step3: Analyze the second compound

The second compound is an aromatic ketone. The carbonyl is conjugated with the aromatic ring, and its carbonyl stretching frequency will be around 1680 - 1640 cm⁻¹.

Step4: Analyze the third compound

The third compound is an $\alpha,\beta$ - unsaturated ketone. The carbonyl is conjugated with the double bond, and its carbonyl stretching frequency will be around 1680 - 1640 cm⁻¹.

Step5: Conclusion

None of the given carbonyl compounds have a stretching frequency around 1715 cm⁻¹.

Answer:

none of these