Splitting Patterns in ¹H NMR Spectroscopy HL Only
Specification Reference S3.2.11
Quick Notes:
- In ¹H NMR, individual signals may appear as multiplets (clusters of peaks).
- This is due to spin–spin coupling: interaction between nonequivalent neighbouring protons.
- Peak spltting follows the n + 1 rule:
- A proton with n equivalent neighbours causes its signal to split into n + 1 peaks.
- Key patterns:
- Singlet = no neighbours
- Doublet = 1 neighbour
- Triplet = 2 neighbours
- Quartet = 3 neighbours
- Splitting patterns provide structural detail about adjacent groups.
Full Notes:
What Causes Splitting?
When hydrogen nuclei are close together but in different environments, their magnetic fields influence each other.
This causes the signal of one proton to split depending on how many adjacent (neighbouring) hydrogens there are.
The (n + 1) Rule
The number of hydrogens bonded to adjacent, non-equivalent carbon atoms determines how many times the peak is split.
This is summarised by the n + 1 rule.
Where n is the number of protons bonded to adjacent, non-equivalent carbon atoms and n + 1 is the number of times a peak will be split.
This is useful to know when analysing spectra as it means the number of hydrogen atoms bonded to adjacent, non-equivalent carbon atoms can be determined from peak splitting.
Example: Ethanol (CH3CH2OH)
- CH3 group shows a triplet (next to CH2).
- CH2 group shows a quartet (next to CH3).
- OH appears as a singlet (no splitting).
Summary
- Splitting reveals how many neighbouring H atoms are present.
- Use the n + 1 rule to predict and interpret multiplets.
- Combine with other NMR features such as chemical shift and integration to deduce structure.
- Refer to the data booklet for common δ values and fragment clues.