How to Draw Structures for Accurate NMR Predictions

Technical Note How to Draw Structures for Accurate NMR Predictions Version 10 Advanced Chemistry Development, Inc. Toronto, ON, Canada www.acdlabs.com Introduction These rules were developed to conform with the algorithmic requirements of ACD/Labs prediction software 1 (ACD/CNMR, ACD/HNMR, ACD/FNMR, ACD/NNMR, ACD/PNMR, and ACD/2D NMR Predictor). General requirements: 1. ACD/Labs software predicts the spectrum of the actual structure you have drawn. It does not take into account the formation of complexes and salts (intramolecular, with the solvent or in case of

mixtures). 2. 2D structures with stereochemistry must be used as an input to the predictors. Experimental chemical shifts are produced as a result of the 3D environment, but the database of structure matches for the prediction algorithm is made according to the 2D structure representations. So although the 3D environment is accommodated in the prediction result, the 2D structure with stereochemistry must be used as an input. 3. Coordinates (as drawn) are only used to determine the configuration of double bonds as well as of isomers of amides, oximes, hydrazones, and nitrosamines. Key Examples Double Bonds 1. Avoid defining the configuration of a double bond using stereo bonds. Wrong Right O CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 O Z - isomerE - isomer O CH 3 CH 3 CH 3 CH 3 2 Technical Note Algorithms within the software determine the configuration of a double bond using the angle between the single bond of a substitute and the line going through the double bond. If this angle is not 0 o , such a structure is defined as a specific isomer: E or Z: CH 3 CH 3 CH 3...

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