Proton NMR: chemical shift, integration and splitting

Chemical shift (spec 15.20 i)

Each peak is a different proton environment, measured relative to TMS at δ 0. Approximate shifts (data booklet values apply in the exam):

Peak areas (spec 15.20 ii)

The area under each peak (shown by an integration trace or given as a ratio) is proportional to the number of hydrogen atoms in that environment. Ethanol, CH3CH2OH, gives a ratio 3 : 2 : 1.

Splitting: the n + 1 rule (spec 15.20 iii, iv)

In a high-resolution spectrum, a peak is split by the protons on adjacent carbon atoms that are in a different environment. n neighbouring H gives n + 1 lines:

• 0 neighbours: singlet; 1: doublet; 2: triplet; 3: quartet

An ethyl group, -CH2CH3, shows a quartet (CH2, next to CH3) and a triplet (CH3, next to CH2). O-H protons usually appear as singlets and do not split neighbouring peaks. Equivalent protons do not split each other.

Why TMS?

TMS gives a single strong peak because all 12 hydrogens are equivalent, its peak is away from most others, and it is inert and volatile, so it is easily removed.

Worked example

Predict the high-resolution 1H NMR spectrum of ethyl ethanoate, CH3COOCH2CH3.

1. CH3CO-: 3H, no neighbouring H, singlet near δ 2.0
2. -OCH2-: 2H, next to CH3, quartet near δ 4.1
3. -CH2CH3: 3H, next to CH2, triplet near δ 1.3

Answer: Three peaks, ratio 3 : 2 : 3: singlet, quartet, triplet

Check yourself

1. In the 1H NMR spectrum of chloroethane, CH3CH2Cl, how is the CH2 peak split?
   • Triplet
   • Doublet
   • Singlet
   • Quartet
   Show answer

   Quartet. The CH2 has 3 neighbouring H on the CH3: 3 + 1 = 4 lines.

2. What is the peak area ratio in the 1H NMR spectrum of propanoic acid, CH3CH2COOH?
   • 3 : 3 : 1
   • 3 : 2 : 1
   • 2 : 2 : 2
   • 1 : 1 : 1
   Show answer

   3 : 2 : 1. CH3 (3H), CH2 (2H), COOH (1H).

3. A 1H NMR spectrum has a peak at δ 9.7. Which group is present?
   • A CH3 next to C=O
   • An alkane CH3
   • An alcohol C-H
   • An aldehyde -CHO
   Show answer

   An aldehyde -CHO. Aldehyde protons appear at about 9 to 10 ppm.

4. How many peaks are in the low-resolution 1H NMR spectrum of propan-2-ol, (CH3)2CHOH?
   Show answer

   3. Six equivalent CH3 protons, one CH proton and one OH proton: 3 environments.

5. In the 1H NMR spectrum of 2-methylpropane, (CH3)3CH, how is the peak for the nine CH3 protons split?
   • Singlet
   • Triplet
   • Doublet
   • Decet
   Show answer

   Doublet. Each CH3 is next to a carbon with one H: 1 + 1 = 2 lines.

6. A compound C3H6O has a single peak in its 1H NMR spectrum. What is it?
   • Propanone
   • Propanal
   • Propan-1-ol
   • Prop-2-en-1-ol
   Show answer

   Propanone. Propanone, CH3COCH3, has six equivalent protons.

7. Why is TMS chosen as the reference in 1H NMR?
   • It absorbs at the highest chemical shift
   • It contains carbon-13 only
   • Its 12 equivalent protons give one strong peak, and it is inert and volatile
   • It reacts with the sample to make it visible
   Show answer

   Its 12 equivalent protons give one strong peak, and it is inert and volatile. A single, sharp, well-separated peak and easy removal.

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Sources

• Pearson Edexcel IAL Chemistry (2018) specification
• Pearson Edexcel IAL Chemistry (2018) scheme of work

Last updated 7 November 2026. Spotted a mistake? Tell us.