The Structure of Pseudohalides-The Existence of a New Isomer

SUPERALKALI MOLECULES CONTAINING HALOGENOIDS

The structure and properties of hypermetalated Li 2X and Na 2X and their corresponding Li 2X+ and Na 2X+ cations utilizing halogenoids X (SCN, OCN, and CN) were investigated using ab initio methods at the CCSD(T)/6-311+G(3df)//MP2/6-311+G(d) level of theory. The vertical ionization potentials of Li 2X and Na 2X radicals were calculated at the outer valence Green function level (OVGF) with the 6-311+G(3df) basis sets. It was found that all Na 2X molecules studied possess the vertical ionization potentials (VIP) that are smaller than the IP of the Na atom (5.14 eV) and thus may be termed superalkali molecules, whereas the Li 2X radicals exhibit slightly larger IPs. The smallest VIP of 4.728 eV was calculated for the Na 2 CN system. The IP dependence on the structure and the singly occupied molecular orbital (SOMO) character is also discussed.

Ab initio computational insight into the ion-pair SN2 reaction of lithium isothiocyanate and methyl fluoride in the gas phase and in acetone solution

The ion-pair S(N)2 reaction LiNCS + CH3F with two mechanisms, inversion and retention, was investigated at the MP2(full)/6-311+G**//HF/6-311+G** level in the gas phase and in acetone solution. All HF-optimized structures were confirmed by vibrational frequency analysis. Based on IRC analyses, eight possible reaction pathways in the title reaction are proposed. The inversion mechanism through a six-membered-ring transition-state structure is the most favorable. Methyl thiocyanate should form preferentially in the gas phase and the more stable methyl isothiocyanate will be the main product in CH3COCH3. The retardation of the reaction in CH3COCH3 solution was attributed to the differences in the solvation free energies in the separated reactants and transition structures. All of the theoretical results are consistent with the experiment.