Connection Tables Chemical Abstracts Service

The WLN was applied to indexing the Chemical Structure Index (CSI) at the Institute for Scientific Information (ISI) [13] and the Ituiex Chemicus Registry System (ICRS) as well as the Crossbow System of Imperial Chemical Industries (ICl). With the introduction of connection tables in the Chemical Abstracts Service (CAS) in 1965 and the advent of molecular editors in the 1970s, which directly produced connection tables, the WLN lost its importance. 

The Chemical Abstracts Service has institutionalized the use of graphic representations for identification of and retrieval of information about chemical compounds through their Graphical Data Stmcture (GDS) and connection table (CT). Two information packages. Messenger and STN Express, are the basis for this on-line retrieval system (42). 

As a compound is represented by a square matrix having a number of rows and columns equal to its number of atoms, it is clear that such a representation cannot be used for input purposes, but is rather an internal representation of structures and reactions. Furthermore, as the numbering of the atoms in a chemical compound is a priori arbitrary, several connectivity tables can be deduced from a given compound. Thus, special algorithms are required to obtain a canonical connectivity table. For example, the Chemical Abstracts Services have recourse to an algorithm devised by Morgan [234]. 

A connection table has been defined [6] as a uniquely ordered list of the node symbols of the structure (or graph) in which the value (atomic symbol) of each node and its attachment (bonding) to the other nodes of the total structure are described , though it does not have to be unique. The Chemical Abstracts Service (CAS) Registry III connection tables [7] are unique, however, and that for hydroquinone is illustrated in Figure 1 ... 

The computer translation of systematic chemical nomenclature into chemical structures is now possible. At least three groups have software which demonstrates this. Chemical Abstracts Service has for a long time used software running on mainframe computers to translate names in its style of nomenclature into connection tables. More recently, the Beilstein Institute has developed the VICA name interpreter for an IBM 3090 mainframe. This translates with a high success rate a wide range of names into a connection table using a dictionary of some 3000 name fragments. ... 

The Chemical Abstracts Service (CAS) Chemical Registry System was initially installed in 1965. The current version of the system, called Registry IB, has been in operation since 1974. The Registry System now contains records for more than 10 million chemical substances, with 97% represented in the form of atom-bond connection tables. 

CAS = Chemical Abstracts Service CSD = Cambridge Stmctural Database CT = connection table DBMS = database management system MDL = Molecular Design Ltd. RN = registration number, RTECS=Registry of Toxic Effects... 

CAS = Chemical Abstracts Service CT = connection table GFDB = Gmelin Factual Database ICSD = Inorganic Crystal Structure Database MF = molecular formula NIST = US National Institute of Standards and Technology STN = Scientific and Technological Network. 

CAS = Chemical Abstracts Service CT = connection table IDC = Internationale Dokumentationsgesellschaft fiir Chemie (International Documentation Society for Chemistry) 1ST = inorganic structure table ROSDAL = representation of structure description arranged linearly SDF = strucmre distribution file. 

BRCT = Beilstein Registry Connection Table BRN = Beilstein Registry Number CAS = Chemical Abstracts Service CNOC = Commission on the Nomenclature of Organic Chemistry CT = connection table ICRS = Index Chemicus Registry System ISI = Institute for Scientific Information RN = CAS Registry Number SCN = Structure Code Number SSSR = smallest set of smallest rings WLN = Wiswesser Line-formula Notation. 

The first solution uses some algorithm that transforms any connection table of a molecule into a unique, canonical, form. The best known of these, the Morgan algorithm, chooses the numbering based on the numbers and properties of the neighbors of each atom of the structure. It is the basis of the Chemical Abstracts System Chemical Registry Service. There is also a canonicalization scheme for the SMILES notation of a chemical structure. ... 

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