Friday, July 11, 2008


Now that you know about the three main approaches, where to go from here?
If you want to use one of the methods for fitting a spin system (see yesterday's post), the simplest (and single) thing to do is to read the manual of your program. If it's too short, reading it will require a little investment of time. If it doesn't help, it either means that your program is extremely intuitive or that you need a different program. If, instead, the manual is very long, there are two cases: either the program is very powerful and well documented, so there's a lot of things to learn from it, or the program and its manual are a crappy mess.
There are a lot of advantages if the same program performs both processing and simulation; it means: less things to learn, a couple of export/import operations are avoided, there are more users (i.e. the program has been more tested), the interface is probably simplified (because they are general-purpose programs targeted at the casual user). The disadvantages (compared to a specialized program) may be a limited set of features.
It's also extremely convenient if the same program implements all the three fitting methods outlined yesterday AND dynamic NMR. This gives you the option to switch with no effort from any method to any other. If, instead, you use a different program for each method, and the first method you try turns out to be inappropriate, you have to redeclare the terms of your problem and re-import the experimental data... quite boring!

Comparing different programs
Not all programs are equal. Features to look for when comparing two of them:

  1. Can you adjust the parameters manually (graphically)?

  2. Are the plots (experimental and theoretical) overlapped?

  3. Can you define symmetry relations?

  4. How many systems can you define?

  5. Can you define relations between parameters of different systems?

  6. How many nuclei can you define?

  7. Can you define all kinds of spins?

  8. Are dipolar couplings handled?

  9. Is Dynamic NMR included?

  10. Is Total-Lineshape Fitting included?

  11. Is a LAOCOON-like Fitting included?

  12. Can you change the shape of the peaks or are they exclusively Lorentzian?

  13. Are the chemical shifts measured in ppm rather than in Hz?

  14. Can you declare a spin system by its ChemDraw formula?

  15. Once you have extracted the parameters, can you generate formatted lists of these parameters? How many formats?

  16. If your program includes a "multiplet analyzer", does it talk with the simulation module?


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