SUPPORTING INFORMATION Molecular-tailoring: Reaction path control with bulky substituents Tibor Szilvási and Tamás Veszprémi* *Corresponding author. E-mail: Tveszpremi@mail.bme.hu To confirm the reliability of the chosen B97-D functional and estimate the error bar, we have carried out a short benchmark study on hydrogen substituted tetrapersila compounds (2a-5a). CCSD(T)/cc-pVTZ, RI-B97-D/cc-pVTZ, B3LYP/cc-pVTZ and M06-2X/cc- pVTZ energies (E, in Hartree) were computed at RI-B97-D/6-31G* optimized geometries (Table S1). Since our main conclusions are drawn from the relative stability of optimized structures on a PES, Table S1 contains the relative energies (∆E, in kJ/mol) compared to 5a, respectively, for all computed energy results. The relative difference compared to CCSD(T)/cc-pVTZ results are also shown (∆∆E) in Table S1 in kJ/mol (∆∆E=∆E CCSD(T) - ∆E DFT ). As one can see in Table S1, ∆∆E clearly indicates that the relative error is reasonable for RI-B97-D method (RMS = 10 kJ/mol) similar to that of the most popular B3LYP and M06-2X DFT methods (RMS are 13 and 14 kJ/mol, respectively). The error bar is estimated by that about ±15 kJ/mol for this small molecules. For large molecules with real substituent, the error bar is obviously greater, which is expected to be about ±30 kJ/mol. Since our main results are based on the elimination of unwanted minima protecting only one, error bars have negligible role in this study. Table S1. CCSD(T)/cc-pVTZ, RI-B97-D/cc-pVTZ, B3LYP/cc-pVTZ and M06-2X/cc- pVTZ energies (E, in Hartree) were computed at RI-B97-D/6-31G* optimized geometries. Relative energies are given (∆E, in kJ/mol) compared to 5a, respectively, for all computed energy results. The relative difference compared to CCSD(T)/cc-pVTZ results are also shown (∆∆E, in kJ/mol) (∆∆E=∆E CCSD(T) -∆E DFT ).