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Organic Synthesis and Analysis

High resolution proton NMR

  • 3 things to know
  • Component 2

Overview

Recall questions on what splitting adds to a low resolution spectrum, the n+1 rule and the singlet, doublet, triplet and quartet patterns, why equivalent hydrogens do not split each other, why an OH peak is a broad singlet, and identifying a compound from a full set of patterns.

What you need to know

Answer each one before you reveal it.

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Key term

Outline the order in which spectral evidence is used to elucidate a structure.

Key term

What extra information does a high resolution proton NMR spectrum give over a low resolution one?

Key term

State the n+1 rule.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What extra information does a high resolution proton NMR spectrum give over a low resolution one?

    Model answer

    Each peak is split into a group of lines, and the splitting shows how many hydrogen atoms are on the neighbouring carbon atom.

  2. 2

    State the n+1 rule.

    Model answer

    A peak is split into n plus one lines, where n is the number of hydrogen atoms on the adjacent carbon atom.

  3. 3

    What splitting pattern arises from two hydrogen atoms on the adjacent carbon?

    Model answer

    A triplet, three lines in the height ratio 1 : 2 : 1.

  4. 4

    What splitting pattern arises from three hydrogen atoms on the adjacent carbon?

    Model answer

    A quartet, four lines in the height ratio 1 : 3 : 3 : 1.

  5. 5

    Why is the methyl peak of ethanol a triplet?

    Model answer

    The adjacent CH₂ group carries two hydrogen atoms, and two plus one is three.

  6. 6

    Why do hydrogen atoms in the same environment not split one another?

    Model answer

    They resonate at the same frequency, and identical nuclei produce no observable splitting between themselves.

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