We pursue dynamic charge and occupancy modulation of silicon dangling bond sites on H-Si(100)-2 X 1 with a biased scanning tunneling microscope tip and demonstrate that the reactivity and mechanism of product formation of cyclobutylmethylketone (CBMK) on the surface at the active sites may be thus spatially regulated Reactivity is observed to be dependent on the polarity between tip and surface while the area over which reactivity modulation is established scales according to the dopant concentration in the sample. We account for these observations with examination of the competition kinetics applicable to the CBMK/H-Si reaction and determine how said kinetics are affected by the charge state of DB sites associated with reaction initiation and propagation. Our experiments demonstrate a new paradigm in lithographic control of a self assembly process on H-Si and reveal a variant to the well-known radical mediated chain reaction chemistry applicable to the H-Si surface where self assembly is initiated with dative bond formation between the molecule and a DB site.