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Spectroscopy and Chromatography

Deducing a structure from an nmr spectrum

  • 3 things to know
  • Unit A2 2

Overview

Ethyl ethanoate splitting pattern and one limitation of proton nmr.

What you need to know

Answer each one before you reveal it.

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Key term

What three pieces of information does an nmr spectrum give?

Key term

In what order should a spectrum be worked through?

Key term

A compound of formula C₂H₆O shows a single peak. What is it?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What three pieces of information does an nmr spectrum give?

    Model answer

    The number of peaks gives the number of hydrogen environments, the integration gives how many hydrogens are in each, and the splitting gives how many hydrogens are on the neighbouring carbon.

  2. 2

    In what order should a spectrum be worked through?

    Model answer

    Count the environments, read the integration ratio against the molecular formula, use the chemical shifts to identify the groups, then use the splitting to connect them.

  3. 3

    A compound of formula C₂H₆O shows a single peak. What is it?

    Model answer

    Methoxymethane, since both methyl groups are equivalent, whereas ethanol would give three peaks.

  4. 4

    A compound of formula C₃H₆O gives one singlet at 2.1 parts per million. What is it?

    Model answer

    Propanone, whose six hydrogens are all equivalent and lie next to a carbonyl.

  5. 5

    A compound of formula C₃H₆O gives a triplet, a multiplet and a peak near 9.7 parts per million. What is it?

    Model answer

    Propanal, with the aldehyde hydrogen far downfield.

  6. 6

    A compound of formula C₄H₈O₂ shows a quartet at 4.1, a singlet at 2.0 and a triplet at 1.3, in the ratio 2 : 3 : 3. Identify it.

    Model answer

    Ethyl ethanoate, with the OCH₂ downfield next to oxygen, the acetyl methyl a singlet, and the chain methyl a triplet.

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