Question

Why is the C-O absorption band of 1-hexanol at a smaller wavenumber (1060 cm^-1) than the C=O absorption band of pentanoic acid (1220 cm^-1)?

Short answer

Pentanoic acid has a carbonyl group (-C=O), which means double bond character is present. While 1-hexanol has an alcoholic group where the single bond between carbon and oxygen is present, which is pure.

Step-by-step solution

Effect of bond order

The bond order increases its absorption band wavenumber is also increases.

Functional group

Carbonyl groups have higher wavenumber as compared to the alcoholic group.

Pentanoic acid has a carbonyl group (-C=O), which means double bond character is present. It is a strong bond and requires more energy to stretch.

While 1-hexanol has an alcoholic group where the single bond between carbon and oxygen is present, which is pure.