The maximum number of product lists returned can be specified in the command line parameter --pieces. By default, Reactor returns all product lists.
If the --extract parameter is specified, then only the required product lists are returned (by default, all products specified in the reaction equation are returned). The required products are specified by 1-based product indexes according to the reaction equation. For example, -x 1 returns only the first product while -x 1,3 returns the first and the third products. Note that this comma-separated list of product list indexes should not contain whitespace characters.
The command line parameter --single sets to process unambiguous reactions only, where each reactant has a single reaction site. If any of the reactants has more or less than one reaction site then reactor won't return any product.