Theoretical calculations MRCI, CASSCF

The halogenation reaction of ethylene has been modeled by many researchers [170, 172-176], For chlorination in apolar solvents (or in the gas phase), the formation of two radical species requires the use of flexible CASSCF and MRCI electronic structure methods, and such calculations have been reported by Kurosaki [172], In aqueous solution, Kurosaki has used a mixed discrete-continuum model to show that the reaction proceeds through an ionic mechanism [174], The bromination reaction has also received attention [169,170], However, only very recently was a reliable theoretical study of the ionic transition state using PCM/MP2 liquid-phase optimization reported by Cammi et al. [176], These authors calculated that the free energy of activation for the ionic bromination of the ethylene in aqueous solution is 8.2 kcalmol-1, in good agreement with the experimental value of 10 kcalmol-1. 

Throughout this work, several systems are discussed and the specific theoretical level is indicated in each case. The adopted notation is given as follows. CASSCF calculations including n electrons, m orbitals and averaging k states is denoted as SA-fc-C ASSCIm). If all CAS configurations are used to build the reference space for the MRCI procedure, it is referred to simply as MRCI. On the other hand, if a different space with p electrons and q orbitals is used, it is denoted MRCI(/ , q). The Cl expansion includes either all single and double excitations (MR-CISD) or... 

The most comprehensive theoretical study of nitrogen pentafluoride so far comes from Hettinger et al., [19], They report an investigation of this molecule at several high levels CASSCF, MRCI, B3LYP, MP2, and CC with variants of these methods and of basis sets, some species were studied at 15 different levels. The ealeulated stmcture and, of prime interest, the calculated thermodynamic and kinetic stabihties, are given. In contrast to some earlier studies Synthesis, below), these workers are optimistic about the possibility of preparing NF5. 

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