In OEChem TK, the name canonical SMILES is used for a unique SMILES string that encodes the connection table of a molecule, but no chiral or isotopic information. Consequently, two stereoisomers always share the same canonical SMILES, since their stereo information are ignored during the canonicalization process. For generating a canonical SMILES, use the OECreateCanSmiString function.
OEChem TK‘s canonical SMILES terminology corresponds to Daylight‘s ‘unique‘ SMILES definition.
In OEChem TK, the name canonical isomeric SMILES is used for a unique SMILES string that also encodes isotopic and stereo information. Due to the unambiguity of canonical isomeric SMILES, they can be used as a universal identifier for a specific chemical structure. For generating a canonical isomeric SMILES, use the OECreateIsoSmiString or the preferred high-level OEMolToSmiles function.
OEChem TK‘s canonical isomeric SMILES terminology corresponds to Daylight‘s ‘absolute‘ SMILES definition.
In OEChem TK, an atom is considered chiral, if it is connected to four different substituent groups i.e. its mirror image is non-superimposable.
In OEChem TK, an easily invertible nitrogen, i.e. a non-planar nitrogen with one attached hydrogen, is not considered to be chiral. This is due to the fact that trivalent nitrogen compound undergo rapid inversion that interconvert enantiomers.
In OEChem TK, a double bond is considered chiral, if the cis and trans forms of this bond represent two distinct isomers. A chiral bond can be either a chain bond or a ring bond that does not belong to any ring smaller than 8-membered.
Originally developed by the International Union of Pure and Applied Chemistry (IUPAC), the IUPAC International Chemical Identifier (InChI) is a character string generated by computer algorithm. It is a tool to be used in software applications designed and developed by those who choose to use it.
The InChI algorithm turns chemical structures into machine-readable strings of information. InChIs are unique to the compound they describe and can encode absolute stereochemistry making chemicals and chemistry machine-readable and discoverable.
The InChI format and algorithm are non-proprietary and the software is open source, with ongoing development done by the community. A number of IUPAC working groups is currently creating standard for those areas of chemistry that are not yet handled by the InChI algorithm.
To make the InChIKey the InChI string is subjected to a compression algorithm to create a fixed-length string of upper-case characters. While the InChI to InChIKey hash compression is irreversible, there are a number of InChI resolvers available to look up an InChI given an InChIKey.
LINGO is a very fast text-based molecular similarity search method. It is based on fragmentation of canonical isomeric SMILES strings into overlapping substrings.
In OEChem TK, a bond is considered rotatable only if it is a single non-ring bond between two non-terminal, non-triple-bonded atoms. For example the following structures have no rotatable bonds:
SMIRKS is a reaction transform language. A reaction considered valid according to the strict SMIRKS semantics if:
The strict semantics also requires that unmapped reactant atoms are destroyed in the reaction.
The strict semantics means that in full compliance with the SMIRKS defined by its originator, Daylight Inc. For more information about the semantics of SMIRKS language visit http://www.daylight.com/dayhtml_tutorials/languages/smirks/index.html.
In OEChem TK the atom stereo information is stored as a relative positions of neighboring atoms around a tetrahedral center. If an atom has specified stereochemistry, then the OEAtomBase.HasStereoSpecified method returns true.
In OEChem TK atom stereochemistry is internally represented by two properties stereo atom and chiral atom. These properties are completely independent and allows OEChem TK to retain configuration information around atoms that are not chiral atom, or to identify chiral atoms whose configuration is not specified.
In the current version of OEChem TK, the only class of stereochemistry supported for atoms is OEAtomStereo_Tetrahedral which corresponds to \(sp3\) tetrahedral chirality. Valid return values for the OEAtomStereo_Tetrahedral stereochemistry class are OEAtomStereo_Left and OEAtomStereo_Right.
In OEChem TK the bond stereo information is stored as a relative positions of neighboring atoms around a bond. If a bond has specified stereochemistry, then the OEBondBase.HasStereoSpecified method returns true.
In OEChem TK bond stereochemistry is internally represented by two properties stereo bond and chiral bond. These properties are completely independent and allows OEChem TK to retain configuration information around bonds that are not chiral bonds, or to identify chiral bonds whose configuration is not specified.
In the current version of OEChem TK, the only class of stereochemistry supported for bonds is OEBondStereo_CisTrans which corresponds to conjugated E/Z chirality. Valid return values for the OEBondStereo_CisTrans stereochemistry class are OEBondStereo_Cis and OEBondStereo_Trans.