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--- structurelevels [2012/10/15 12:24] – created sanmark
+++ structurelevels [2012/10/15 12:33] – sanmark
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 //**Compounds**// refer to chemical compounds that can be represented by multiple molecular structures, i.e. with multiple tautomeric and protonation forms. Their [[stereonotations|stereo configuration]] can be well-defined as well as fully or partially unknown / undefined, similarly to the case of //structures//.
+^Structure specification level ^Identical                                           ^Different ^
+|Compound                      |Mesomers, tautomers, protonation states, conformers | Stereoisomers |
+|Structure                     |Mesomers, conformers                                | Stereoisomers, tautomers, protonation states |
+|Conformer                     |Mesomers                                            |Stereoisomers, tautomers, protonation states, conformers |
+Chemical structures with different stereo configurations are distinguished at all specification levels. Depending on the stereo configuration type, they represent a single isomer or a set of potential isomers and/or mixtures of isomers. (figure) Their stereo configurations are treated identical if and only if the represented isomers / set of isomers are identical. If the configuration differs, the chemical structures are treated as different database entries.
+//Compounds// can have more symmetries than //structures//. In //compounds// neither the number of hydrogens nor the position of some hydrogens are fixed. A //compound// can represent all realistic tautomeric and protonation states (//structures//). Therefore those asymmetry centers that are present only in one potential //structure// (tautomer and protonation state) are not treated as stereogenic at the //compound level//. Similarly, some cis-trans bonds found a //structure// might be missing from the corresponding //compound//.