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Products - NMR Prediction Prediction of 1H-NMR and 13C-NMR shift values based on 4000 parameters for 13C NMR and almost 3000 parameters for 1H NMR, chemical shifts are predicted using additivity rules and several strategies of approximation.
Model
Data Set
Output
Prediction Quality
Limitations
References


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Model

Chemical shifts are predicted for all hydrogen or carbon atoms for which additivity rules are available. For a given molecule, the appropriate substructures are automatically assigned following a hierarchical list. These substructures provide the base value of a final predicted shift. Ring systems not available in the data set are approximated by embedded rings and, if necessary, even disassembled into acyclic substructures.

For each substructure found, the remaining parts of the molecule are treated as substituents. Substituents contribute to a final shift by its increments added to the base value. If increments for those substituents are not available so-called embedded substituents, smaller structural units with the same neighbouring atoms, are applied automatically. Or increments of identical or embedded substituents of a corresponding substructure are taken assuming that the effects of the substituents are of the same magnitude.

Models for ethylenes (cis/trans) and cyclohexanes (eq/ax) are also implemented. To use this feature, cyclohexanes must be drawn in the chair conformation.


Data Set


The data set for the 1H-NMR prediction currently contains 700 base values and about 2000 increments. The 13C-NMR prediction tool is based on 4000 parameters.


Output


The output consists of three parts:
1 - the molecular structure with the predicted shifts
2 - a detailed protocol of the prediction process

Question marks given instead of shift values mean that there are no appropriate substructures available in the data set. Shift values in parentheses indicate that the prediction is not complete, that means that the effect of one or more substituents could not be predicted based on data set used.


Prediction Quality


In case of 1H-NMR, shifts of about 90 % of all CHx-groups can be predicted with a mean deviation of 0.2 - 0.3 ppm. The use of polar solvents may strongly increase these deviations.
In case of 13C-NMR, over 95 % of the shifts can be predicted with a mean deviation of 3.8 ppm.


Limitations


1H-NMR shifts of hydrogen atoms bonded to hetero atoms are not predicted because they are not only affected by solvents but also by concentration, impurities and steric effects.

In condensed cyclohexane-like rings, gamma corrections cannot be applied for predicting 13C-NMR shifts.


References


  • R. Bürgin Schaller, M. E. Munk and E. Pretsch, J. Chem. Inf. Comput. Sci. 36, 239-243 (1996).
  • R. Bürgin Schaller, C. Arnold and E. Pretsch, Anal. Chim. Acta 312, 95-105 (1995).
  • R. Bürgin Schaller, E. Pretsch, Anal. Chim. Acta 290, 295 (1994).
  • E. Pretsch, A. Fürst, M. Badertscher, R. Bürgin and M. E. Munk, J. Chem. Inf. Comp. Sci. 32, 291-295 (1992).
  • A. Fürst, E. Pretsch, Anal. Chim. Acta 229, 17 (1990)




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