♦ C=O tension at 1735 cm ^-1 . If there are conjugated double bonds with the carbonyl, the band shifts to lower values. When the double bond is on the alkoxy group (-OR) of the ester, a shift towards higher values is observed.

♦ CO tension: 2 bands at 1300 and 1000 cm ^-1 . Being wider and more intense the one observed at 1300.

Observe how the conjugation on the main chain, which presents methyl benzoate, decreases the frequency of the C=O tension band. However, the conjugation presented by phenyl acetate produces an increase in said frequency.