Detailed analyses of model Sn2 reactions : CH3X + F- (X = F, Cl, CN, OH, SH, NH2 and PH2)
Gonzales, Jason Mathew
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The detailed analysis of gas-phase SN2 reactions is the focus of this dissertation. It is split into two major parts. In Part I several of the commonly utilized density functional techniques are evaluated in the analysis of SN2 reactions of the type CH3X + F− (X = F, Cl, CN, OH, SH, NH2 and PH2). The accuracy of these methods has been compared to a CCSD(T)/TZ2Pf+dif reference. With regards to structural predictions only the B3LYP hybrid functional may be considered to give adequate structures, with the pure functionals oﬀering poorer agreement with the reference. In evaluating energetics all of the functionals perform very poorly, particularly for barrier energetics involving the transition state. The pure functionals often underestimate the barrier by over 4 kcal mol−1. B3LYP is marginally better, averaging a deviation of 2 kcal mol−1. Part II of this work is a high-level determination of the aforementioned SN2 energetics to within ± 1 kcal mol−1, through the use of the focal point analysis. This technique entails extrapolation to the one-particle limit for the Hartree−Fock and MP2 energies using basis sets of up to aug-cc-pV5Z quality, inclusion of higher-order electron correlation [CCSD and CCSD(T)] with basis sets of up to aug-cc-pVTZ quality, and addition of auxillary terms for zero-point vibrational energy, core correlation and scalar relativistic eﬀects. In addition to the focal point analyses, energy decomposition schemes have been utilized to partition the ion-molecule complexation energies, namely the Morokuma-Kitaura (MK), Reduced Variational Space (RVS), and Symmetry Adapted Perturbation Theory (SAPT) techniques.