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Chemistry LibreTexts

NMR Spectroscopy (Quinones-Fernandez)

  • Page ID
    296329
  • Learning Objectives

    After completing this exercise, students should be able to:

    1. Sketch and draw molecules in the software.
    2. Visualize and recognize the differences between frequency, line width, and number of points for resolution in the 1H NMR.
    3. Recognize the peaks’ positions related to the proton in the molecule by observing the NMR spectrum.
    4. Distinguish the spin-spin coupling in the spectrum.

    Students will do the questions in class and the software simulation at home.

    Table 1. List of the compounds that will be simulated in the 1H NMR software.

    Compound Name

    Chemical Formula

    3-methyl-2-butanone

    C5H10O

    Benzaldehyde

    C7H6O

    Benzylamine

    C7H9N

    cyclobutane

    C4H8

    methanol

    CH3OH

    phenol

    C6H5OH

     

    1. Draw each molecule and estimate where would you observe each of the protons of the molecule in the 1H NMR spectra.

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

    1. For each molecule, evaluate and estimate the splitting pattern that you may observe in the 1H NMR spectra.

       

       

       

    1. Discuss the differences that you will observe if the molecules are characterized by using a 100 MHz and a 500 MHz NMR instrument.

       

       

       

    1. Would the resolution of the spectra change if you use a change the line width and number of points in the NMR instrument? Explain.

       

       

       

       

       

       

       

       

       

     
    1. Open nmrdb.org(https://www.nmrdb.org/new_predictor/index.shtml?v=v2.95.0).

      Sketch each molecule in the software.

    1. Compare your above estimations with the data obtained in the NMR prediction. Do you observe any major differences from what you thought the results would be to what is obtained using the NMR simulator?

       

       

       

       

    1. Verify the splitting pattern of each of the molecules to what you predicted. Do you observe any differences?

       

       

       

    1. Change these options one at a time:
      1. Frequency (60, 200 and 500 Hz)
      2. Line width (1, 5, and 10 Hz)
      3. Number points (16,64 and 256k)

      Anytime you change any parameters click “Simulate spectrum” to observe the changes in the NMR spectrum.

      Discuss how these changes affect the NMR spectrum for one of assigned molecules from Table 1.

     

     

     

     

     

     

     

     

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