6.9.3

Hydrogen-1 NMR (A2 Only)

Test yourself

1H Environments

1H NMR is the next type of NMR we will study. It is slightly harder than 13C NMR but the basic principles are the same.

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Chemical shifts

  • As in 13C NMR, 1H NMR spectra display signals at different chemical shift values.
  • These chemical shift values represent different 1H environments.
    • E.g. If the spectrum has four peaks, there are four different chemical environments with an unknown number of 1H's in each environment.
  • We can use chemical shift tables to identify 1H environments and functional groups from the signals in spectra.
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Tetramethylsilane

  • As in 13C NMR, 1H NMR's reference is tetramethylsilane (TMS).
    • TMS has a chemical shift of 0 ppm.
    • TMS produces a single peak because each 1H in TMS is in the same environment.
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Signal ratios

  • An extra piece of information that 1H NMR gives us over 13C NMR is based around the ratio of the areas underneath the signals.
  • The ratio of the areas reflects the ratio of how many protons are in that same environment.
    • E.g. If there are two singlet peaks and one peak is twice as big as the other, this means that the chemical environment of the bigger peak has twice as many 1H's as the other environment.

Splitting Patterns

1H NMR gets slightly harder than 13C NMR when we consider splitting patterns. But, this pays off because it gives us lots of useful information.

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Signals splitting

  • In 1H NMR, the main signals that represent different chemical environments have fine splitting patterns.
  • The main signal may be split into a number of fine peaks. Peaks have different names depending on how many splits they have:
    • No splittings = singlet.
    • Split into two = doublet.
    • Split into three = triplet.
    • Split into four = quartet.
      • On the AQA spec, anything split into five or more = multiplet.
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Information from splittings

  • Signal splitting helps us work out the number of 1H's in different environments. Beware, this is not straightforward!
    • Number of fine splittings = number of 1H's on adjacent carbon + 1
      • This is called the n+1 rule.
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Example: Diethyl ether

  • There are only two different proton environments in diethyl ether.
    • The adjacent CH2 and CH3 groups creates the splitting patterns seen above.
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Example: Propanol

  • CH3 group: split into a triplet due to adjacent CH2 group.
  • Middle CH2 group: split into a multiplet () due to adjacent CH2 group on one side and CH3 group on the other side.
  • CH2 group next to -OH: split into a triplet due to adjacent CH2 group.
  • OH group: is a singlet as no adjacent carbons.
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Jump to other topics

1Physical Chemistry

2Physical Chemistry 2 (A2 Only)

3Inorganic Chemistry

4Inorganic Chemistry 2 (A2 Only)

5Organic Chemistry 1

6Organic Chemistry 2 (A2 Only)

6.1Optical Isomerism (A2 Only)

6.2Aldehydes & Ketones (A2 Only)

6.3Carboxylic Acids & Esters (A2 Only)

6.4Aromatic Chemistry (A2 Only)

6.5Amines (A2 Only)

6.6Polymers (A2 Only)

6.7Biological Organic (A2 Only)

6.8Organic Synthesis (A2 Only)

6.9NMR Spectroscopy (A2 Only)

6.10Chromatography (A2 Only)

6.11A-A* (AO3/4) - Organic 2

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