The SYBYL line notation or SLN is a specification for unambiguously describing the structure of chemical

Chemistry

Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

 molecule

Molecule

A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

s using short ASCII

ASCII

The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...

 strings

String (computer science)

In formal languages, which are used in mathematical logic and theoretical computer science, a string is a finite sequence of symbols that are chosen from a set or alphabet....

.
SLN differs from SMILES in several significant ways. SLN can specify molecules, molecular queries, and reactions in a single line notation whereas SMILES handles these through language extensions. SLN has support for relative stereochemistry, it can distinguish mixtures of enantiomer

Enantiomer

In chemistry, an enantiomer is one of two stereoisomers that are mirror images of each other that are non-superposable , much as one's left and right hands are the same except for opposite orientation. It can be clearly understood if you try to place your hands one over the other without...

s from pure molecules with pure but unresolved stereochemistry. In SMILES aromaticity

Aromaticity

In organic chemistry, Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. The earliest use of the term was in an article by August...

 is considered to be a property of both atoms and bonds whereas in SLN it is a property of bonds.

Examples

Elemental atoms are specified by the standard abbreviation of the chemical elements. Atom attributes follow the atom name in square brackets. C[I=14] indicates carbon-14 isotope. Hydrogens are normally explicitly specified as a shorthand, CH4 is the SLN for methane. In addition to elemental atoms SLN supports the specification of wild card atoms: Any (match any atom), and Hev (match any heavy atom). It also has an extensive Markush syntax for specifying combinatorial libraries and RGROUP queries. SLN has several query atom types for matching groups of atoms. Each type has the group name, followed by an optional positive integer.

Group	Description
R	Used to match a side chain. Matched atoms must not have any connection to the core
X	Used to match side chains and rings. Atoms matching an X group can match side chains and rings
Rx	Matches side chains and rings, a ring closure must match a second Rx group

See also

• Simplified molecular input line entry specification
  Simplified molecular input line entry specification
  The simplified molecular-input line-entry specification or SMILES is a specification in form of a line notation for describing the structure of chemical molecules using short ASCII strings...
  
   (SMILES notation)
• Smiles arbitrary target specification
  Smiles arbitrary target specification
  SMiles ARbitrary Target Specification is a language for specifying substructural patterns in molecules. The SMARTS line notation is expressive and allows extremely precise and transparent substructural specification and atom typing....
  
  (SMARTS notation)