Introducing the electron-withdrawing carbonyl group on the aldehyde substrate changes the PES significantly (Figure .A and 7). The pathway to epoxide is kinetically unfavourable in the aldehyde selective reaction and higher in free energy than the corresponding TS1. TS2 structures to the epoxide have a ΔG ‡ of at least 6.72 kcal mol -1 , which corresponds to a ΔΔG ‡ = 5.16 kcal mol -1 when compared to the most stable TS2 structure. In the epoxide selective reaction, the ΔG ‡ for TS2 structures to the epoxide are approximately 1 kcal mol -1 . On the other hand, the corresponding TS2s to aldehyde and ketone have comparable kinetic barriers with a ΔG ‡ in the range of 1.2-3.5 kcal mol -1 in both the epoxide and aldehyde selective reaction. The change in the energy barrier of the epoxide pathways results in the process being dynamically controlled and lead to different chemoselectivities. We conducted Hirshfeld charge analyses and studied the charge distribution by functional groups on key TS structures (SI Section 4.C). The differences in charge distribution are insignificant across TS2s from both reactions. However, in TS1(SS-1) of the epoxide selective reaction (ΔG ‡ = 4.43 kcal mol -1 ), the COPh group on the aldehyde withdraws negative charges and is noticeably less positive compared to the corresponding Ph group in the TS1(RS-1) of the aldehyde selective reaction (ΔG ‡ = 7.59 kcal mol -1 ). The chemoselectivity of the epoxide selective reaction is dynamically controlled by the trajectory from TS1 and the presence of the COPh group affects the charge distribution in TS1.