Question

what is the stretching frequency (in cm⁻¹) of the following carbonyl?
o 1685
o 1655

Explanation:

Step1: Identify the carbonyl type

The given compound is an amide with conjugation. Conjugation lowers the carbon - oxygen double - bond stretching frequency.

Step2: Recall amide and conjugated carbonyl frequencies

Amide carbonyls typically have stretching frequencies around 1650 - 1690 cm⁻¹. Conjugation further lowers the frequency. For a conjugated amide, the carbonyl stretching frequency is closer to 1655 cm⁻¹.

Answer:

1655