Although esters typically have carbonyl stretching frequencies at about 1740 cm -1 in the infrared spectrum, the

Question:

Although esters typically have carbonyl stretching frequencies at about 1740 cm^-1 in the infrared spectrum, the corresponding band for lactones can vary greatly with ring size. Three examples are shown in the margin. Propose an explanation for the IR bands of these smaller ring lactones.

1735 cm- 1770 cm- 1840 cm-