SGroup

SGroup, short for Structural Group, is a modeling construct used in chemical informatics to represent substructures that are treated as a single unit within a molecule. SGroups are especially useful for encoding polymers, Markush-type substituents, and other recurring substructures in a compact form, rather than expanding them into explicit atom-bond graphs.

An SGroup defines a set of member atoms and bonds, a designated type, and associated properties that govern how the group attaches to the rest of the molecule. Commonly used types include RGroup (representation of substituent groups) and Repeat Unit (a unit that may repeat within a polymer). SGroups may specify linkage points, constraints on repetition, and other attributes such as naming or data fields. In practice, SGroups are stored in chemical file formats such as MDL Molfile V3000 as separate records that reference the included atoms without duplicating their connectivity.

SGroup support enables software to perform tasks such as substituent enumeration, polymer property estimation, and substructure searches without fully expanding all repeating or generic parts of the structure. Modern cheminformatics toolkits typically provide read and write support for SGroups, though implementations can vary between formats and vendors, and historical data may require conversion.

See also: Markush structures, polymer chemistry, molfile, substructure search.