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Logic Puzzle #35: Assigning Chemical Shifts … Solution

October 5, 2012

Coupling information is very useful in locating the position of an atom in relation to other atoms. This puzzle covers one such example.

For an unknown compound1, the 13C assignment is not clear for carbons 116 or 134 ppm. The 13C NMR spectrum shows the 19F-13C coupling for the carbon at 116 ppm as 23.7 Hz and the carbon at 134 ppm as 9.2 Hz. Typical 19F-13C coupling constants for the carbon in the ortho position is ~20 Hz while the meta position is ~10 Hz2. Therefore, the correct assignment is indicated in box B.

Thank you Djalma for your comment on puzzle #35.

  1. Cohen, D.T., Eichman, C.C., Phillips, E.M., Zarefski, E.R., Scheidt, K.A., Angew. Chemie. Int. Ed. 2012, 51, 7309-7313.
  2. Hans J. Reich, 2011


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