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Integrated Problems 16.78 Do you think 'H NMR or 13C NMR spectroscopy would be more suitable for distinguishing among compounds A, B, and C? Explain. 0 0

Answer 1

16.78.

¹H NMR would be more suitable.

In ¹³C NMR, all 3 compounds will show 3 peaks as all of them have 3 chemically inequivalent carbon atoms.

z YV IX N 0 X, Y, and Z represents the 3 chemically inequivalent carbon atoms in the compounds

In ¹H NMR, all 3 compounds will show 2 peaks as all of them have 2 chemically inequivalent carbon atoms. One of the peak is due to the aldehyde protons and the other peak is due to the aromatic protons. But unlike ¹³C NMR, the peaks in the proton NMR can be integrated to know the ratio of protons in each peak.

For compound A,

aromatic protons : aldehyde protons = 4 : 2 = 2 : 1

For compound B,

aromatic protons : aldehyde protons = 3 : 3 = 1 : 1

For compound C,

aromatic protons : aldehyde protons = 2 : 4 = 1 : 2

H H H The hydrogens marked in red and blue in each compound are chemically equivalent but their ratio is different. Hence, peak integration in 'H NMR would be useful to distinguish them.

Hence, ¹H NMR would be more suitable for distinguishing among compounds A, B, and C.