Question

what is the stretching frequency (in cm⁻¹) of the following carbonyl?
1765
1715
1775 and 1810
1685

Explanation:

Step1: Identify the carbonyl type

The given compound is an ester - like carbonyl. Esters generally have carbonyl stretching frequencies in the range of 1735 - 1750 \(cm^{-1}\) for aliphatic esters. However, the presence of the adjacent carbonyl and the ring structure can cause some shifts.

Step2: Analyze the options

1765 \(cm^{-1}\) is in the general range for carbonyl stretching of esters with some possible electronic - effects from the adjacent groups. 1715 \(cm^{-1}\) is more typical for ketones or aldehydes in some cases and not for this ester - like carbonyl. The range 1775 - 1810 \(cm^{-1}\) is too high for this type of carbonyl, usually associated with highly conjugated or strained carbonyls like acid anhydrides. 1685 \(cm^{-1}\) is too low and is more characteristic of conjugated carbonyls like in amides or some enones.

Answer:

1765