Question

question 3
what is the stretching frequency (in cm⁻¹) of the following carbonyl?
1715
1745

Explanation:

Step1: Identify the carbonyl type

The given compound is a cyclic enone. Conjugation lowers the carbon - oxygen double - bond stretching frequency.

Step2: Recall typical frequencies

A normal aliphatic ketone carbonyl stretches around 1715 - 1720 $cm^{-1}$, and a conjugated carbonyl (like the one in the cyclic enone) has a lower frequency than a non - conjugated one. The stretching frequency of a non - conjugated five - membered ring ketone is around 1745 $cm^{-1}$, but conjugation shifts it to a lower value.

Answer:

1715