[lespaul]

Hi everyone,

Just wondering is there is an observable difference in IR spectra between a ester and a lactone? I know the lactone is simply a cyclic ester, so maybe their is no difference at all. Just curious to see if the cyclic conversion would affect the spectra in any way.

[Corribus]

It depends a lot on how many members there are in the ring. As the number of atoms in the ring (n) goes toward infinity, a lactone and ester become functionally identical. Generally you start to notice a difference as n < 6. When n = 5 or lower, the carbonyl stretch shifts to shorter wavelengths (higher energy).