Question

Tell precisely how you would use the proton NMR spectra to distinguish between the following pairs of compounds.

Short answer

(a) Based on chemical shift values

(b) Based on the number of signals

(c) Based on the chemical shift values

(d) Based on the chemical shift values

Step-by-step solution

Theory of 1H NMR Spectrum

¹H NMR spectrum is the plot of intensities of peaks versus the chemical shift in ppm. It provides the information about the structure of the compound based on the splitting pattern observed in the spectrum.

Detailed answer of part (a)

The CH₂ group of protons for ethyl chloride or second compound has a higher chemical shift value as compared to ethyl bromide because chlorine is more electronegative than bromine.

Detailed answer of part (b)

The first compound shows 2 signals and second compound shows 3 signals as shown in the image with different colors:

Detailed answer of part (c)

The chemical shift for the hydrogen attached to carbonyl carbon in the firstcompound will be around 9.5–10 ppm whereas the chemical shift for CH₂ protons attached to carbonyl carbon in the secondcompound will show chemical shift values of around 2.0–2.6 ppm.

Detailed answer of part (d)

The chemical shift for the hydrogen attached to carbonyl carbon in the first compound will be around 9.5–10 ppm, whereas the chemical shift for CH₃ protons attached to oxygen in the secondcompound will show chemical shift values of around 3.0-4.0 ppm.