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A structural unit annotation consisists of a one-character
boundary descriptor
(BD), which is a
formal open bond. A structural unit
annotation is atom-anchored.
A BD separates a structural unit from the overall
molecular structure to which the unit belongs. BD annotations are
used to encode formal parts of a molecule. Depending on context,
these parts are commonly referred to as
substructures,
motifs,
fragments
or (functional) groups.
Each character that is a valid bond symbol in CurlySMILES can
be a BD.
| BD |
Meaning in CurlySMILES annotation |
| - |
open or dangling single bond
(see encoding example given for
protecting group BIBS)
|
| = |
open double bond |
| # |
open triple bond |
| $ |
open quadruple bond |
| : |
open (in-ring) aromatic bond |
| ~ |
open bond of unspecified type
|
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