Thermal (300K) and electron-induced reactions of benzene (Bz), chlorobenzene (ClPh), 1,2-dichlorobenzene (1,2-diClPh) and 1,4-dichlorbenzene (1,4-diClPh) with Si(100)2×1 have been examined by Scanning Tunneling Microscopy (STM). Thermal reactions of Bz yielded predominantly the quadruply--bound Tight Bridge, TB, configuration on top of the Si dimer-rows. For ClPh and 1,2-diClPh, which resembled one another, thermal reaction led with 45-50% yield to the doubly--bound Butterfly, BF, configuration, also on top of the dimer-row, and with 20% yield to a novel "Displaced", D, configuration to one side of a dimer-row. The adsorbate 1,4-diClPh was alone in favouring a configuration in which neighbouring dimer-rows were "linked" (L) by a bright-feature centrally located between the dimer-rows. By ab initio calculation, we interpret D as due to the rupture of one C-Cl bond per adsorbate molecule, and L to the rupture of two C-Cl's. The breaking of this weak bond is followed in the former case by attachment of the aromatic ring to one dimer-row, and in the latter to attachment to two adjacent dimer rows. Application of a -5V voltage pulse to the STM tip substantially increased the percentage of row-linking structures, L, for 1,4-diClPh, but neither -5V nor +4-6V volt pulses resulted in L-type binding of Bz. The postulated L product of 1,4-diClPh, with an aromatic ring linking the two inner Si atoms of adjacent dimer-rows and the two Cl's on the outer Si atoms of the dimer-rows, is shown to be in accord with ab initio simulation of the observed STM image.