CH···O hydrogen bonds involving formyl groups have been invoked as a crucial factor controlling many asymmetric transformations. We conducted quasi-classical direct molecular dynamics simulations on the phosphoric acid-catalyzed allylboration of benzaldehyde to understand the synergy between the phosphoric acid OH···O hydrogen bond and the secondary CH···O formyl hydrogen bond as the reaction occurs. In the gas phase, both the CH···O and OH···O hydrogen bonds are enhanced from reactants to transition states. In toluene, the trend of H-bond enhancement is observed with a smaller magnitude because of solvent caging. The strength of the formyl hydrogen bond in the TS, a second CH···O interaction between the P═O oxygen and ortho-hydrogen of the phenyl ring and the OH···O hydrogen bond were determined using quantum mechanical calculations (4.6, 1.0, and 14.5 kcal mol−1, respectively).We are grateful to The English-Speaking Union (Lindemann Trust Fellowship to M.N.G.), Girton College, Cambridge (Research Fellowship to M.N.G.) and the NSF (CHE-1361104 to K.N.H.) for financial support. Computational resources were provided by the UCLA Institute for Digital Research and Education (IDRE) and the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by the NSF (OCI-1053575)
