Question

For Enalapril (drug): Indicate expected absorptions in IR above 1500 cm -1

Answer 1

Enalapril structure is

As we can see clearly, there is an ester, amine, amide, aromatic ring, and carboxylic acid groups

1) Carboxylic acid O-H stretch signal is very strong and broad in the region 2500-3300 cm-1, hence aromatic =C-H stretch, sp3 C-H stretch, amine and amide N-H stretch all are overlapped with this signal, so we can't observe them.

2) Only observable that too overlapped each other signals are ester, amide, carboxylic acid C=O stretch in the region 1640 - 1750 cm-1

3) even ester & carboxylic acid C-O stretch also will not well resolved in the region 1000 - 1300 cm-1

4) aromatic C=C stretch and sp3 C-H bending vibrations also overlapped in the region 1400 - 1600 cm-1 because sp3 C-H bending region is 1350 - 1480 cm-1. In addition amine & amide N-H bending vibration near 1600 cm-1 is also overlapped.

Totally a complex spectrum obtained and analysis is very complicated, i think better go for NMR spectra.

Hope this helped you!

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