The SYBYL line notation or SLN is a specification for unambiguously describing the structure of chemical molecules using short ASCII strings.
SLN can specify molecules, molecular queries, and reactions in a single line notation whereas SMILES handles these through language extensions.
Like SMILES, SLN is a linear language that describes molecules.
Attributes, bracketed strings with additional data like [key1=value1, key2...], is a core feature of SLN.
When searching for molecules, comparison operators such as fcharge>-0.125 can be used in place of the usual equal sign.
Anything that starts with an uppercase letter identifies an atom in SLN.
Attributes defined for atoms include I= for isotope mass number, charge= for formal charge, fcharge for partial charge, s= for stereochemistry, and spin= for radicals (s, d, t respectively for singlet, doublet, triplet).
It also has an extensive Markush syntax for specifying combinatorial libraries and RGROUP queries.
is used for zero-order bonds, similarly to reaction SMILES, although a + is preferred for distinct molecules.
The s= attribute is defined for double bonds, to convey stereochemistry information in E–Z (E/Z) or cis–trans (c/t) notation.