These rules were developed to conform with the algorithmic requirements of ACD prediction software (ACD/CNMR and ACD/HNMR) and IUPAC recommendations and, thus, with the algorithm requirements of ACD/Name.

General requirements:

ACD software (ACD/CNMR and ACD/HNMR) predicts the spectrum of the actual structure you have drawn. It does not take into account:

Tautomeric forms (even most preferable ones);

Formation of complexes and salts (intramolecular, with the solvent or in case of mixtures).

The 3 dimensional representation of a structure is taken into account only for predicting ³J constants in HNMR spectra. It is not used when chemical shifts are predicted.

Coordinates (as drawn) are only used to determine the configuration of double bonds as well as of isomers of amides, oximes, hydrazones and nitrosamines.

Examples

Double bonds

Avoid defining the configuration of a double bond using stereo bonds.

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:

Do not draw two substituents on one side of a double bond.

The configuration of the double bond in cyclic structures should be as shown, with double bonds drawn with Z-configuration (not E-configuration).

Other types of isomerism

Amide isomers should be drawn with defined substituent positions.

Similar rules should be applied to isomers of oximes, hydrazones and nitrosamines.

Stereo Bonds and Orientation of Substituents

The orientation of substituents should be drawn with the help of stereo bonds.

Besides the orientation of substituents, in bicyclic structures it is necessary to show the orientation of a bridge.

Stereo bonds should be designated in such a way that they show not only the mutual orientation of substituents in a cycle but also the configuration of all chiral carbon centers (and, if possible, of phosphorus, sulfur, etc.).
Avoid drawing consecutive stereo bonds ("head" to "tail"). In other words, it's preferable to draw two neighboring asymmetric centers so that they are connected with a single bond, but configuration of both of is shown differently.

Do not use stereo bonds only for the purpose of display.

All sugars and their derivatives should be drawn with stereo bonds.

Explicit Hydrogens

For spectral prediction, do not use explicitly drawn hydrogens, except in some special cases.

Use explicit hydrogens:

To define the configuration of fusion atom in the fused cycles:

To avoid drawing stereo bonds directly one after another: