Question

Question:Rank the following compounds from highest wavenumber to lowest wavenumber for their C=O absorption bands:

a.

b.

Short answer

Answer

The decreasing order of wavenumber is as shown below.

a.

b.

Step-by-step solution

Inductive electron-withdrawing group

The group that attracts the ring’s electron toward itself is the electron-withdrawing group.The oxygen of the ester group has electron-withdrawing nature; that’s why the double bond character of the carbonyl group increases, and its wavenumber is the highest.

Electron donating group

The group that releases its electrons to the ring is the electron-donating group. If the concentration of hydrogen molecules is higher, its O-H stretch absorption wavenumber is high. While a diluted solution with less hydrogen bonding or no hydrogen bonding has less O-H stretching absorption wavenumber.

Ring size

The size of the ring increases the stretching wavenumber decreases.

So, the order is as follows.

a.

b.

Order of decreasing wavenumber