Question

please answer #5

5. Which type of spectroscopy (IR, 'H NMR, and/or "C NMR) would be good to distinguish between propanal and propanoic acid? State what you would observe for each compound in each type of spectroscopy and whether that type of spectroscopy would be a good way to distinguish between the two compounds.

Answer 1

5) IR spectroscopy is good to distinguish both. Because in IR spectroscopy, different peaks are observed for different bonds hence different functional groups can be distinguished easily.

In IR of propanal, C=O stretching peak appear around 1700 and two aldehydic C-H stretching peak appear at 2780-2880.

In IR of propanoic acid, C=O peak appear around 1715 and broad peak around 3300 appear for O-H stretching.

In 1H NMR, propanal give peak around 10ppmfor aldehydic proton and in propanoic acid, peak appear around 11 ppm. It can also distinguish both but to less extent.

In 13C NMR, both give peak around 180 ppm and difficult to distinguish.