Simulating a simple 1D experiment with 5 spins: A₃B₂ spin system

Here we will give explicit step-by-step instructions for simulating a 1D proton spectrum for a 5-spin system (A₃B₂) similar to that in e.g. bromoethane.

STEP 1: Define the Spin System:

The spin system selected for this example consists of 5 protons: three A-protons and two B-protons, coupled with each other by a scalar coupling. In the case of bromoethane, the A-protons represent the methyl group and B represent the methylene group. For simplicity, we will set scalar couplings between the three A-spins to 15 Hz, between the two B-spins to 12 Hz, and those between the A and B spins to 7 Hz.
Use the pull-down panel to select 5 spins. 
Then click on the ‘spin setup’ button. This brings up the spin setup dialogue. Select the ‘Graph Mode’ button. 

The graph mode is a user-friendly way to input chemical shifts and couplings. Pressing that button opens the graph mode window shown below.

Enter 1.23 for the chemical shift value for the first nucleus. 
Here you can also define the type of the nucleus, its spin-relaxation rates, and the concentration of the molecular species that this atom belongs to. For example, enter 0.8 and 1.0 (reciprocal seconds) for R1 and R2, respetively, -- we will use these values of the relaxation rates for all other spins.

Now let us define resonance frequencies for all other nuclei. Click on the box for the first atom once to remove the blue highlight. 

Click on the box for the second atom (it should become blue).

Enter 1.23 for the chemical shift and 0.8 and 1 (reciprocal seconds) for R1 and R2. Continue entering the chemical shifts for the rest of the atoms. Here’s a table of the chemical shifts:

Remember to deselect one atom (click it so it isn’t blue) before moving to the next.

Once all of the chemical shifts have been entered, define scalar couplings between spins.

Deselect the atoms so that none are highlighted. Now select atom one (highlighting it) and then select atom two.

A line will form between them.  Enter a coupling of 15 Hz in the box under ‘J’.

Continue selecting pairs of atoms and input 15 Hz for scalar couplings between spins 1, 2, and 3, 12 Hz between spins 4 and 5, and 7Hz between these two groups of spins. Once finished the ‘Graph Mode’ window will look like this:

Finally, click on the ‘Update’ button to save/input your data into VNMR. This takes you back to the ‘spin setup’ window.

Now we are ready to set up experimental conditions for the simulation.

Open Experimental Setup Panel and set experiment dimension to 1D:

Return to the Main Panel, select pulse sequence zg, and then click on the XLATE button to translate it. If the translation is successful, the ZG button will turn green.

Open Program Parameters panel and set pulse sequence parameters: in this case the only parameter that is not assigned and requires to be set is the recycling delay d1.

Program Parameters:


Set d1 to 5s.

Open Experimental Setup Window and set the carrier position (Op(1)=2 ppm in this example), the number of acquired experimental points you wish to simulate (td1 = 1024), and the desired spectral width (SWp1=2ppm) :All relevant entries in the program parameter window will be updated automatically.

Click on the ZG (green) button -- this will start the simulation.

Open Data Processing window, set zero-order phase correction PHC0=180 and check out the Phase Correction button.

Click on the Process button to process the simulated FID, and then on the REAL button to display real part of the resulting spectrum.