“…From (c) to (h) in Figure , different cycloaddition reactions are shown: [2+2] CN (c), [2+2] CC (d), [4+2] NN (e), [4+2] CC (f), [4+2+2] CC (g), and [4+2+2] NN (h). A [4+2+2] cycloaddition refers to a surface reaction between 4π electrons from the adsorbate molecule and 2π electrons for each surface dimer (see Figure g,h); a previous work refers to these reactions as “cross-row” or “cross-bridge” reactions. ,, In all these cases, the aromaticity of the adsorbate is disrupted, as previously shown in studies of pyridine and pyrazine on Si(100) surfaces. , While this is enthalpically unfavorable, the accessibility of pathways that allow for reduction of the aromatic character can be attributed to a small increase in entropy, creating a thermal switch between aromatic and nonaromatic adsorbate configurations. , …”