Question

3) You have two boxes of pills ;red and blue; they fall and you have to identify, which pill is which substance. The substances where paracetamol and ASA and their chemical structure was given. There were spectra of HNMR for the red pills and the blue pills.

Answer 1

The chemical structure of paracetamol and ASA are given below:

The NMR spectra of paracemaol and ASA are useful to identify these compounds. ASA has carboxylic acid functional group which gives signal beyond 10 ppm (~12 ppm) in the 1H-NMR spectrum. This signal is D2O exchangeable and disappears after addition of D2O.

Paracetamol has two exchangeabe protons (NH and OH), which gives signal around 9ppm to 10 ppm.

The signals of aromatic protons are also distinct. Paracetamol has para-disubsituted phenyl ring which give two doublets in aromatic region (6 ppm to 8 ppm). ASA has ortho disubstituted phenyl ring which being unsymmetrical gives multiple signals.

Thus, the pill whose 1H nmr gives two doublet in aromatic region and has two D2O exchageble signals near 9ppm to 10ppm is paracetamol and another one is ASA.