Transition state dynamics and a QM/MM model for the Cl– + C2H5Cl SN2 reaction

A MP2/6-31G* direct dynamics simulation is used to study the dynamics of the central barrier [Cl-C2H5-Cl]– for the Cl– + C2H5 SN2 reaction. The majority of the trajectories move off the central barrier to form the Cl––C2H5Cl complex and appear to undergo efficient IVR as assumed by RRKM theory. However, some of the trajectories move directly to products without forming the complex, a non-RRKM result. A hydrogen atom link-atom QM/MM model is described for studying the dynamics of [X-CH2R-Y]– central barriers with the -R substituent. The model is used to calculate vibrational frequencies for the [Cl-C2H5-Cl]– central barrier.Key words: SN2 reaction dynamics, RRKM theory, QM/MM model, central barrier dynamics, direct dynamics classical trajectories.

13C Chemical shifts for 4-substituted phenylvinyl ethers, sulfides, and selenides: evidence concerning the relative abilities of O, S, and Se to transmit electronic effects

13C chemical shifts for β carbons of 4-substituted phenylvinyl ethers, sulfides, and selenides plus previous data for styrenes indicate that the relative ability of link groups to transmit electronic effects between conjugative groups is S > Se ≈ — > O (where — refers to no link group, i.e. styrene). However, marked deviations from additivity are noted for C(1) chemical shifts which may indicate that O deactivates the ring to electronic substituent effects while S and Se activate the ring. If this explanation is valid then the actual ability of the link atom to transmit electronic effects is — > O > S > Se.