Spectrum Prediction using Podocarpane as an Example
 
 
 Example #1:

In this example the stereochemistry is given by up/down-bonds except at position 4 (C-6 within the drawing) where the two methylgroups are located. From the drawing it is unspecified which methylgroup is in axial or equatorial position respectively, therefore the methylgroups can't be distinguished resulting in a predicted value of 26.5ppm for both of them with a fairly large expectation range of 15.6-34.5ppm. (the methylgroups are numbered C-16 and C-17 within the drawing)

 
Example #2:

In the second example the missing piece of information is inserted by defining the axial methylgroup using an up-bond. The other methylgroup is automatically assigned to the equatorial position leading to a dramatic improvement of the prediction quality. The estimated values for these methylgroups differ now by ca. 12ppm caused by 1,3-diaxial interaction as to be expected.
 

Example #3:
 
This example is identical to example #2 except that the definition of the stereochemistry is done in a different way - in any case the identical result for the predicted spectrum must be obtained !
Example #4:
 
This example must give an identical result to examples #2 and #3, because a redundant information about stereochemistry has been introduced.
 
 
From the examples given above it can be seen that the CSEARCH-software has no problems in understanding different definitions of stereochemical situations and translating them into the program internal canonical representation before starting the spectrum estimation process.
 
Last update: 06-Apr-2001
(Wolfgang Robien)