Reaction Searching with WebReactions
A major activity for synthetic chemists is to find literature precedents for a reaction query, either a particular transformation of a specified compound or a more general search for matching analogs at various levels of similarity. As reaction databases became available for the computer, the traditional searching mode has been via the structures of reactant and product.
However, reactions are very complex if described in terms of the full structures of reactant and product, and so only a few thousand entries can be easily searched in a reasonable time. This structure-based search is too cumbersome for a database of 1-2 million reactions. It will also not easily find analogs of the query reaction defined in somewhat different or more general terms.
WebReactions introduces a new concept for the retrieval of reactions from a large database in which reactions are indexed instead by the bond changes which occur. When a synthetic chemist thinks of a reaction, he envisions first the making and breaking of bonds at the reaction center as the defining nature of the reaction. Subsequently he considers the effects of surrounding groups, i.e., on rate, hindrance, or resistance to change under the reaction conditions. The WebReactions program mirrors this approach for indexing reaction entries in any database.
The solution to the problem of retrieval speed is to generalize and abstract the reaction entries first with a rough but rigorous description of the reaction change itself. This then affords a basis for an index of all the entries ordered by the groupings of this generalized format. Hence when a query is also formulated in the same terms, the first search instantly brings up all matched entries since they are all grouped together in the index.
In this way we capture very fast a relatively tiny subset which contains all relevant samples, irrespective of what structures are attached unchanged around the reaction center. This in turn provides a much smaller field for further search, so that subsequent retrieval for more detail is much faster.
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