We have examined the reaction of the Ge(100)-2 x 1 surface with five-membered cyclic amines including pyrrolidine, 3-pyrroline, pyrrole, and their N-methyl-capped analogues. The reactions of pyrrolidine, N-methylpyrrolidine, pyrrole, and N-methylpyrrole were also probed on the Si(100)-2x1 surface for comparison. Multiple internal reflection (MIR) infrared spectroscopy in combination with density functional theory (DFT) cluster calculations were used to study the reactions. We find that for the aliphatic amines, dative bonding of the N lone pair to the electrophilic down atom of the surface dimer competes with N-H dissociation and [2 + 2] cycloaddition. to form stable surface adducts at room temperature and is the major surface reaction observed on the Ge(100) surface. At higher coverages, some evidence for N-H dissociation is seen on the Ge(100) surface. For pyrrole and N-methylpyrrole, the aromatic system of pi electrons is seen to have profound effects on their reactivity with the Si(100) and Ge(100) surfaces. The delocalized system of pi electrons allows a kinetically favored alternative pathway for N-H dissociation via dative bonding at a ring carbon, resulting in the facile N-H dissociation of pyrrole on the Ge(100) surface, in contrast to the case for aliphatic amines. Evidence is obtained suggesting that pyrrole and N-methylpyrrole also undergo electrophilic aromatic substitution reactions at the surfaces, reactions that have not been previously observed for benzene and other aromatic molecules. We have also compared the known reactivity of pyrrole with its reactivity on Si(100) and Ge(100) and have found interesting similarities, demonstrating that principles used to understand the chemistry of organic molecules can also be applicable and useful for understanding bonding at semiconductor surfaces.