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Table 1 Overview of possible changes to the environment of an atom. Changes are detected by comparing atoms that are mapped to each other. In each example case, the changes in the environment of the blue atom are assessed. This is done by either comparing the two blue atoms directly (for radicals, charges and stereo), or by comparing the surroundings (bond changes)

From: Automated reaction database and reaction network analysis: extraction of reaction templates using cheminformatics

Changes in environment Example Description
Losing/gaining neighbors Comparing neighbors of ‘A’ and their bonds to ‘A’ to those of ‘A’s mapped counterpart. A match is found if all neighboring element names are equal and all neighboring mapping indices are equal
Changing bond orders Comparing the order of ‘A’s bonds to those of ‘A’s mapped counterpart. Marked if the bond order between ‘A’ and a neighbor has changed
Losing/gaining radicals Comparing single electron count of ‘A’ to its mapped counterpart
Losing/gaining charge Comparing charge on ‘A’ to that on ‘A’s mapped counterpart
Changing stereo configuration Comparing E/Z or R/S configuration of ‘A’ to that of its mapped counterparts