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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.

Chemical shifts

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.
Tetramethylsilane

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.
Signal ratios

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.

Signals splitting

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.
Diagram
Information from splittings

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.
Example: Diethyl ether

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.
Diagram
Example: Propanol

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.
Diagram
Jump to other topics
1

Structure - Models of the Particulate of Matter

2

Structure - Models of Bonding & Structure

3

Structure - Classification of Matter

3.1

The Periodic Table: Classification of Elements

3.2

Periodic Trends

3.3

Group 1 Alkali Metals

3.4

Halogens

3.5

Noble gases, group 18

3.6

Functional Groups: Classification of Organic

3.7

Functional Group Chemistry

3.8

Alkanes

3.9

Alcohols

3.10

Halogenoalkanes

4

Reactivity - What Drives Chemical Reaction?

5

Reactivity - How Much, How Fast & How Far?

6

Reactivity - The Mechanisms of Chemical Change

7

Measurement, Data Processing & Analysis

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