Question

Rank the following compounds from highest wavenumber to lowest wavenumber for their C¬O absorption band:

Short answer

The order followed as:

Step-by-step solution

Wavenumber of carbonyl

Wavenumber of carbonyl is defined as the stretching frequency of the bond and showing absorption in presence of the different functional groups in the IR region of absorption of the single body of carbonyl C-O is 1124-1087$c{m}^{-1}$

Wavenumber order of given carbonyl

The order followed as:

The first carbonyl shows maximum wavenumber because the presence of the lone pairs on the oxygen show delocalization into two forms.

Wavenumber order of given carbonyl

The third compound shows minimum wavenumber because carbonyl has more single bond character due to the contribution from the other two resonance contributors as shown below: