The Cannizzaro reaction (“RX C”) and the benzoin reaction (“RX B”) were investigated by density functional theory calculations. Reaction models (benzaldehyde)2 + X− + (H2O)n [for X− = OH− (RX C) n = 8, and for X− = CN− (RX B) n = 8 or n = 14] were adopted. Three transition states (TSs) were obtained for RX C, and the rate-determining step was confirmed to be the hydride shift. The single electron transfer path was also obtained, which is supported by the C–O−⋯CH
O attraction. In RX B, seven TSs were obtained. The C⋯C bond formation TS, TS4(B), was found to be the rate-determining step. However, the carbanion-formation TS (TS3(B)) and the CN− release TS (TS7(B)) are also of large activation free energies (ΔG‡s). The result ΔG‡(TS4(B)) ≥ΔG‡(TS7(B)) ∼ΔG‡(TS3(B)) was obtained with both n = 8 and n = 14 models. Proton relays along the linear hydrogen bonds are concerned with bond interchanges and promote well arranged and successive elementary processes in RXs C and B.
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