Spin-Spin Splitting Exercise

  1. Double click on the icon "nmrfid".
  2. Select "User-Defined Set of Frequencies".
  3. Click on the "CONTINUE" button.
  4. Select "2 or More Coupled Protons (First-Order Splitting" and Click on the "CONTINUE" button.

    5. The purpose of this exercise is to get familiar with the splitting pattern caused by neighboring nuclei. We therefore are going to work with two different nuclei only.

    To move from one box to another, use the Tab key or your mouse.

  5. Enter 1 for the "First chem shift" and 1 for "The number of protons".
  6. Enter 2 for the "Second chem shift" and 1 for "The number of protons". It is this last number that will be changing in this exercise.
  7. Select "Chemical Shifts as Delta" and "Add TMS to sample?"
  8. Click "CONTINUE".

    9. The program will prompt you with a "J" box. Simply enter a value between 2 and 15. This term is equal to the separation between the peaks resulting from the spin-spin splitting.

  9. Click "DONE".
  10. Click "DO FID".
  11. Click "CONTINUE".
  12. From the menu bar, choose "Cont" and select "Zero fill".
  13. Select "Do FT".

    14. At this point, we have the NMR spectrum expressed in hertz. We need to change it to "d" expressed in ppm (part per million).

  14. From the menu bar, choose "New View", and select "X-Axis Label"
  15. A dialog box will appear. Select "Delta on X-Axis" and Click "CONTINUE".
  16. From "New View", choose "New Freq. Zero".
  17. Move the cursor toward the singlet peak due to the reference TMS.
  18. Click on "Integrate" from the menu bar.

    19. At this point, we finished with the spectrum. Next steps objective is to save the acquired spectrum.

  19. Click on "Export" and choose " Metafile". A new window will appear. Play with the formatting and when you like what you see, save on the floppy disk as "NMR-1-1" the 1-1 reflects that we had a system made of 1 proton interacting with another system of 1 proton.
  20. Repeat steps1-19, and keep everything unchanged except the number of protons in the second system (Step 6 above) using the following: 2, 3, 4, and then 5. Save the spectra as NMR-1-2, NMR-1-3, NMR-1-4, and NMR-1-5.

What happens to the signal due to one system as you increase the number of protons in the other system?

Repeat the experiment using the following values:

 

Chemical Shift

Number of protons

System 1

1

2

System 2

2

1, 2, and then 3.