A multivalent group is a structural unit that is multiply bonded
to other units. CurlySMILES encoding of such groups uses
structural unit annotations
as demonstrated for terminal groups.
Each atom of a multivalent group that has an open bond is
annotated in such a manner that the annotation reflects the type
of the open bond connecting a group of interest to other groups.
The following examples illustrate encoding of bivalent groups with
two open single bonds:
The following group is tetravalent with two open single bonds,
one open double bond and one open triple bond: