Reading Property Output


Click here for full thread
Forum Vet
11:20:07 AM PST - Wed, Dec 5th 2012
From your question, I really need to urge you to do some reading of the literature and text books on NMR chemical shifts and shieldings. This will teach you how the shielding tensor, the principal components and the isotropic shieldings relate, and what role they play in the experimental spectrum. Depending on the type of experiment, solid state or solution, the information you would need is very different.

Little hint, if you are looking at comparing the difference in chemical shift between two molecules in solution, the isotropic shielding difference is all you would need (as the molecules tumble in the experiment, the tensor components average out).

Bert


Quote:Hhg Dec 5th 4:59 pm
Hello,

I am running NMR shielding calculations. The output looks like:

      Atom:    1  P 
        Diamagnetic
   1001.3545     -0.0000      0.0000
     -0.0000   1001.3545      0.0000
      0.0000      0.0000    997.8388

        Paramagnetic
   -782.7759     -0.0075     -0.0031
     -0.0075   -782.7970      0.0003
     -0.0031      0.0003   -558.6973

        Total Shielding Tensor
    218.5786     -0.0075     -0.0031
     -0.0075    218.5575      0.0004
     -0.0031      0.0004    439.1416

           isotropic =     292.0926
          anisotropy =     220.5735

          Principal Components and Axis System
                 1           2           3
              439.1416    218.5810    218.5551

      1        -0.0000      0.9525      0.3044
      2         0.0000     -0.3044      0.9525
      3         1.0000      0.0000      0.0000

and this
      Atom:    1  P 
        Diamagnetic
    996.2680     -3.5903      0.0000
     -3.5903    998.4667     -0.0000
      0.0000     -0.0000    992.8941

        Paramagnetic
   -764.7397     70.9300     -0.0000
     70.9300   -786.0511      0.0000
     -0.0000      0.0000   -653.5802

        Total Shielding Tensor
    231.5284     67.3396     -0.0000
     67.3396    212.4157      0.0000
     -0.0000      0.0000    339.3139

           isotropic =     261.0860
          anisotropy =     117.3419

          Principal Components and Axis System
                 1           2           3
              339.3139    289.9864    153.9577

      1         0.0000      0.7552     -0.6556
      2         0.0000      0.6556      0.7552
      3         1.0000     -0.0000     -0.0000


I am attempting to measure the chemical shift difference between H3PO4 and HPO4(2-).

I assume that I should use the "Total Shielding Tensor" part, but which of the numbers should I use to find the difference in observed chemical shift between the two molecules?

Thanks,
-DC