Infra Red Spectrum - 5

Infrared spectrum 5: following the oxidation of propan-1-olInfrared spectroscopy can show whether an oxidation has worked, and which product has formed, by looking for the O-H and C=O absorptions.Spectrum A: propan-1-ol (starting material)Broad O-H absorption at about 3200 to 3550 cm^-1. No C=O absorption near 1700 cm^-1.Spectrum B: propanal (distilled off as it forms)Strong C=O absorption at about 1730 cm^-1, with aldehyde C-H absorptions at about 2720 and 2820 cm^-1. The broad O-H absorption has disappeared, which shows that the alcohol has been oxidised and no alcohol remains in the distillate.Spectrum C: propanoic acid (heated under reflux with excess oxidising agent)Strong C=O absorption at about 1710 cm^-1 and a very broad O-H absorption from 2500 to 3300 cm^-1.Using the spectra to check a product• If the distillate still shows a broad O-H absorption at 3200 to 3550 cm^-1 as well as C=O, it is contaminated with unreacted alcohol.• If the aldehyde product shows a very broad O-H absorption from 2500 to 3300 cm^-1, some of it has been oxidised further to the carboxylic acid.Summary: oxidising a primary alcohol makes the C=O absorption appear. Whether the O-H absorption then disappears (aldehyde) or becomes very broad and shifts to lower wavenumber (carboxylic acid) shows which product was made.