Data items in the CHEMICAL_CONN_ATOM category would not, in
general, be used in a macromolecular CIF. See instead the
ENTITY data items.
Data items in the CHEMICAL_CONN_ATOM and CHEMICAL_CONN_BOND
categories record details about the two-dimensional (2D)
chemical structure of the molecular species. They allow
a 2D chemical diagram to be reconstructed for use in a
publication or in a database search for structural and
The CHEMICAL_CONN_ATOM data items provide information about the
chemical properties of the atoms in the structure. In cases
where crystallographic and molecular symmetry elements coincide,
they must also contain symmetry-generated atoms, so that the
CHEMICAL_CONN_ATOM and CHEMICAL_CONN_BOND data items will always
describe a complete chemical entity.