User guide

"NMR references" on page 156 (source citations)
NMR shifts
ChemNMR estimates chemical shifts for all hydrogen or carbon atoms for which additivity rules are available. Fol-
lowing a hierarchical list, it first identifies key substructures of a molecule. A substructure provides the base value for
the estimated shift. For example, benzene would be the key substructure of trinitrotoluene.
When a substructure is a ring system not available in the data, ChemNMR approximates its base shift using embed-
ded rings and, if necessary, will disassemble the ring into acyclic substructures.
ChemNMR views remaining parts of the molecule as substituents of a substructure. Each substituent adds to or sub-
tracts from the base shift of the substructure to which it is attached. Additivity rules determine the increment of each
contribution. If an increment for a substituent cannot be determined, ChemNMR uses embedded substituents—
smaller structural units with the same neighboring atoms. Or, it will use increments of identical or embedded sub-
stituents of a corresponding substructure by assuming that the effects of the substituents are of the same magnitude.
ChemNMR provides a detailed protocol of the estimation process applied. It gives substructures as names, com-
pound classes in most cases, substituents in form of a linear code, respectively.
It also implements models for ethylenes (cis/trans) and cyclohexanes (equatorial/axial)
To view
1
H or
13
C NMR information:
1. Select a structure.
2. Go to Structure>Predict 1H-NMR Shifts or Predict 13C-NMR Shifts.
ChemNMR redraws the molecule with the estimated shifts and displays the information and line spectrum in a new
window.
Modifying NMR frequency
You can change the default NMR frequency of 300 Mhz in ChemDraw Proton NMR predictions.
To change the frequency:
1. Select the structure.
2. While holding down the ALT key, select Predict 1H-NMR Shifts from the Structure menu. The Set Frequency
dialog box appears.
3. Specify the new frequency and click OK.
4. Go to Structure>Predict 1H-NMR Shifts. The predicted NMR spectrum appears.
Note: You can also set the NMR frequency in the ChemNMR tab of Preferences dialog.
ChemBioDraw 13.0
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