Question

question 1
0.25 / 0.5 pts
which of the following carbonyls have a stretching frequency around 1685 cm⁻¹? caution: more than one answer is possible.
none of these

Explanation:

Step1: Recall carbonyl IR - stretching trends

Conjugated carbonyls have lower - frequency stretching vibrations compared to non - conjugated carbonyls. A stretching frequency around 1685 cm⁻¹ is characteristic of a conjugated carbonyl.

Step2: Analyze each structure

The first structure is an $\alpha,\beta$ - unsaturated aldehyde (conjugated), the second structure is an $\alpha,\beta$ - unsaturated ketone attached to an aromatic ring (conjugated), and the third structure is an aromatic ketone (conjugated through resonance with the aromatic ring).

Answer:

All of the given carbonyl structures (the three structures shown, not "none of these")