We have performed on-surface synthesis experiments with compound m1 on two different substrates, namely Au(111) and Au(110). By using scanning tunneling microscopy and spectroscopy (STM and STS), in combination with density functional theory (DFT) calculations, we analyze the chemical structure and electronic properties of the reaction products. Because the C-Br bond is activated at lower temperatures than C-H, Ullmann coupling dominates the initial reaction steps independently of the substrate. That is, instead of the head-to-tail product described in Fig. , head-to-head products like those outlined in Fig. are obtained. The products can include reactant molecules that are either at an angle (e.g. d1 or t1) or collinearly oriented (e.g. d2). Compound d2 and t1 can be formally considered as [2+2] and [2+2+2] aryne cycloaddition products. Importantly, the substrate symmetry determines the reaction outcome: whereas on the flat Au(111) surface the reaction products include both linear and non-linear ("two-dimensional") molecules with a pronounced favoritism for molecular trimers (t1) with three-fold symmetry, on the 2×1 Au(110) reconstruction its linear trenches act as templates that limit the reaction products to collinearly fused reactants (e.g. d2). That is, the substrate templating can be used to steer the reaction outcome and the product's alignment.