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Organic Synthesis, NMR and Chromatography

Carbon-13 NMR Interpretation

  • 3 things to know
  • Papers 2 and 3

Overview

Counting carbon environments, and using them to tell isomers apart.

What you need to know

Answer each one before you reveal it.

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Key term

What does a carbon-13 NMR spectrum tell you?

Key term

What information does a carbon-13 NMR spectrum provide about a molecule?

Key term

What does each peak in a carbon-13 NMR spectrum represent?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What information does a carbon-13 NMR spectrum provide about a molecule?

    Model answer

    The number of different carbon environments in the molecule

  2. 2

    What does each peak in a carbon-13 NMR spectrum represent?

    Model answer

    A different carbon environment (carbons in different chemical surroundings)

  3. 3

    How does the number of peaks in a carbon-13 NMR spectrum relate to the structure of a molecule?

    Model answer

    The number of peaks equals the number of different carbon environments, not necessarily the number of carbon atoms

  4. 4

    What does it mean when two carbon atoms in a molecule give rise to a single peak in carbon-13 NMR?

    Model answer

    The two carbon atoms are in equivalent chemical environments

  5. 5

    How can carbon-13 NMR be used to distinguish between structural isomers?

    Model answer

    Different structural isomers have different numbers and/or positions of carbon environments, giving different numbers of peaks

  6. 6

    If a molecule has a plane of symmetry, how does this affect the number of peaks in its carbon-13 NMR spectrum?

    Model answer

    Symmetry makes some carbon atoms equivalent, reducing the number of peaks below the total number of carbon atoms

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