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NMR Spectroscopy: Flashcards

Revise chemical environments, chemical shift, integration, the n + 1 rule and ¹³C NMR.

10 cardsIntermediate

10 cards

  1. Question
    What four things does a ¹H NMR spectrum tell you?
    Answer

    Number of H environments (signals), type of environment (δ), number of H in each (integration), and number of neighbouring H (splitting).

  2. Question
    What is TMS used for?
    Answer

    It is the reference compound, set at δ = 0 ppm.

  3. Question
    How is chemical shift calculated?
    Answer

    δ (ppm) = shift from TMS (Hz) ÷ spectrometer frequency (MHz).

  4. Question
    Why do H atoms near oxygen appear at higher δ?
    Answer

    Electronegative O pulls electron density away (deshielding), shifting the signal to higher δ (about 3.3–4.3 ppm).

  5. Question
    Give typical δ values for aldehyde, carboxylic acid and aromatic H.
    Answer

    Aldehyde 9–10 ppm; carboxylic acid 10–12 ppm; aromatic 6.5–8.0 ppm.

  6. Question
    State the n + 1 rule.
    Answer

    A signal from H with n equivalent H on adjacent carbons is split into n + 1 peaks.

  7. Question
    What splitting pattern does an ethyl group give?
    Answer

    A quartet (CH₂, next to 3 H) and a triplet (CH₃, next to 2 H).

  8. Question
    How many ¹H NMR signals does propanone give?
    Answer

    One (6 equivalent H), a singlet.

  9. Question
    How can you identify an O–H signal?
    Answer

    Add D₂O: the O–H signal disappears. O–H usually appears as a singlet.

  10. Question
    In ¹³C NMR, where do C=O carbons appear?
    Answer

    About 160–220 ppm.