Reading Property Output

Clicked A Few Times

9:59:15 AM PST - Wed, Dec 5th 2012

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

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

Clicked A Few Times

11:38:47 AM PST - Tue, Dec 11th 2012
Thanks!
Hi Bert, thanks much for your response! The isotropic number is indeed what I needed. I got the information from a paper by D.B. Chesnut, Annual Reports on NMR Spectroscopy, 1989, 21, 51-97. -Dave

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