Fig. 1

Cinnamate dimers and the strain-free dissociation mechanism. a The chemical structures of the studied cyclobutane derivatives. b Mechanisms of dissociation of syn-1 calculated at the uMPW1K/6-31 + G (d) level of the DFT in vacuum. The barrier for rotation around the Ph’C–CPh′ bond of syn-Int’ is comparable to that for syn-Int (3.5 kcal mol⁻¹) but the corresponding rotated syn-TS2’_r conformer is 1.8 kcal mol⁻¹ less stable than syn-TS2’ and bond rotation in syn-Int’ is only important under force (see Supplementary Figs. 1–3 for dissociation mechanisms of anti-1 with and without force)