C638: Inorganic Chemistry Seminar (Spring 2005)

NMR Spectral Simulation Using SpinWorks

(Frank Gao, 3/28/2005)

What is SpinWorks:

SpinWorks is a free NMR software for Windows/PC written by Kirk Marat at the University of Manitoba, Canada. It has two functions:

• Easy basic off-line processing of 1D and 2D NMR data;
• Simulation and iterative analysis of complex second order spectra, including dynamic NMR problems and certain solid state NMR problems.

Download and installation:

The program can be downloaded from ftp://davinci.chem.umanitoba.ca/pub/marat/SpinWorks. Save the SpinWorks_24.zip file on your computer and unzip it. Run the setup.exe program in the unzipped folder and follow the instructions. If you need an "unzip" software, go to the IU knowledge base page and get one from there.

Getting Started

1. Start SpinWorks.
2. Load a 1D sample spectrum (Ortho-dichlorobenzen):
• Select Options --> Data Format... --> DISNMR,
• Select File --> Open... --> click on odcbs.001 in C:\Programs Files\SpinWorks\DISNMR data folder.
3. Take a few minutes to familiarize yourself with the layout of SpinWorks. Try some basic operations with mouse, such as zoom in and out, move the spectrum up and down, left and right, adjust vertical scale, etc. (you are not required to do data processing in this class). If you wonder what each menu/button does, press F1 key for help.
4. Click on Help --> Help Topics, a few tutorials including a simulation tutorial could be found there. A SpinWorks user manual could be viewed with Adobe Reader. 
5. Select File --> Exit to exit the program.

Simulation of Second Order Spectra

SpinWorks uses the NUMARIT algorithm as described in: J. S. Martin and A. R. Quirt, J. Magn. Reson. 5, 318 (1971), and modified by R. Sebastian and others at the University of Manitoba.

AMX System

• An ideal AMX system (first order approximation)


1. Start SpinWorks.
2. Click on the Sim button on the Toolbar. A simulation panel will pop up.
3. Click on the Shifts button on the simulation panel to open a chemical shift (& spin system) editor. Enter the following parameters, then click OK to close the editor.



Note:
(a) In each group, the first parameter is the number of spins. For a single spin A, enter 1; for A₂ enter 2; for AA' enter 2*1.
(b) Chemical shift ( d ) values are entered in Hz, not in ppm. Remember:
         d (Hz) = d (ppm) x "spectrometer frequency" (MHz).
(c) if the species parameter for one group is different from the others, the first order approximation will be applied to this group.

4. Click on the Js button on the simulation panel to open a J coupling editor. Enter -12 for J(A,M), 2 for J(A,X), and 10 for J(M,X). Then click OK to close the editor.
   Note: ONLY edit the numerical part of each entry. DO NOT change the coupling labels, such as J(1,2) J(A,M).
5. Click on the Par button on the simulation panel. On the pop-up simulation parameter editor, change Display Linewidth from 1 Hz to 0.5 Hz, and change Size (data points) from 16384 to 65536. This could make a better appearance of spectrum.
6. Click on the NUMMRIT button on the simulation panel. A simulated spectrum will appear on the screen, containing three groups of peaks at 2, 4, and 6ppm, respectively. Each group (multiplet) consists of 4 peaks as a doublet of doublets with exactly equal intensity. J coupling constants can be easily measured from the doublet spacings. The center of each multiplet indicates the chemical shift of each group.

• A realistic AMX system
 
1. Open the chemical shift editor. Set the species parameter to H for all the three spins. This will get ride of the first order approximation.



2. Click on NUMMRIT on the simulation panel to restart the simulation with the new setup. Examine the spectrum carefully. J coupling constants can still be accurately measured from the doublet spacings. The center of each multiplet gives the chemical shift for each group with a negligible error.
3. Change the chemical shift to 1100 for group 2. Start a new simulation and examine the simulated spectrum. This may still be considered as a first order (AMX) spectrum. However, the J coupling constants and chemical shifts measured directly from the spectrum all have some small error.

ABX System

1. Change the chemical shift to 1010 (and the label to B if you like) for group 2. Start a new simulation. This is now an ABX system. Zoom in on the X multiplet at 6 ppm. Use the cursors to measure the multiplet spacings. Note that they do not relate all that well to the coupling constants! This is a second-order or virtual coupling effect, and is much more common than one might think.
2. Change J(A,X) to 0 and restart the simulation. Note that the X multiplet is still a doublet of doublets, although it is coupled to only one of the other spins. There are two small satellite peaks displaced about 16 Hz from the center of the multiplet. These peaks are an important clue that the spectrum is second order, but are easily lost in baseline noise.
3. Set the chemical shift of B (group 2) to be identical to that of A and restart the simulation. The X multiplet looks like a triplet (with two small satellite peaks) despite the fact that it is only coupled to one other spin.

A Few Things to Remember:

1. Make sure that all the dipolar couplings are set to 0 (click on the Ds button on the simulation panel).
2. Make sure that the spin numbers for each nucleus are set correctly (1/2 by default). To look at the parameters, select Spin System --> Edit Species Spin Values.
3. Do not increase the Transition Threshold (default value is 0.01) on the Simulation Parameter editor.
4. Make sure that all the peaks (transitions) of interest are in the spectral window. If desired, change the Display Width and/or Offset on the Simulation Parameter editor.
5. The Spectrometer Frequency parameter on the Simulation Parameter editor has to be set correctly in order to get a correct ppm value on the frequency axis.

Analysis of the Ortho-dichlorobenzene Spectrum

• See the SpinWorks documentation, page 35-36.

If you have any question about SpinWorks or about this course page, talk to Frank Gao ( , A423A/C237, 855-6821).