Synthetically interesting substructures, numbering

ACS Symposium Series American Chemical Society Washington, DC, 1977. 

As a simple exaitple, we can look at the connection table of 2-butanone-3-ol given above. As we scan column 4 we see that atom 2 has the label 19, meaning ketone and atom 3 has the label 7, meaning secondary alcohol. There are no other elementary functional groups in the molecule, since, as shown in column 2, there are no vinyl or acetylenic carbons. 

The number of atoms intervening between the central atoms of the two functional groups is given as a prefix to the number of the complex functional group. For example, an alpha keto ester is numbered 0.40, a beta ketoester is numbered 1.40, a gamma ketoester 2.40 etc. 

Some substructures of synthetic interest are neither rings nor functional groups but are just hydrocarbon fragments. For example, if the reaction is desulfurization of a 2-substituted thiophene derivative then the product contains a string of four saturated carbons, which are originally part of the thiophene ring, along with the removed sulfur atom. The predominant theme 

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In considering the limitions of disk storage we must further consider the data base of chemical reactions which must be available to the program We have mentioned the number 25,000 as the number of synthetic reactions now existing. This is the present size of the file of Derwent.(2) Naturally, of these 25,000 the most popular 2000 are used more than all of the rest put together. Nonetheless, many molecules of interest have something special about them so that their synthesis may require an unusual reaction. Finally we observe that there is an enormous store of literature observations about reactions which show us that such and such a reaction is inappropriate when such and such a substructure is present because the desired reaction proceeds at a slower rate than that of a side reaction. These must in principle and sooner or later in fact be incorporated into any useful reaction data base. 

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