Vibrational characteristics of CD3CN solution containing Mg(ClO4)2 have been studied by means of infrared and Raman spectroscopy. A large blue shift of 40 cm-1 and a relatively small red shift of 3 cm-1 of the ν2 C⋮N stretch are observed as a result of interactions of CD3CN with Mg2+ and ClO4 - ions, respectively. The Mg2+ ion is preferentially solvated by residual water over acetonitrile. The primary coordination number of Mg2+ in acetonitrile is determined as 6 from the Raman intensities of the C⋮N stretch for free CD3CN and those coordinated to Mg2+. Evidently, formation of contact ion pairs of Mg2+ and ClO4 - is more probable at a high concentration of Mg(ClO4)2. The IR extinction constants of the ν2 and ν4 stretching bands increase dramatically upon coordination. The vibrational characteristics of free CD3CN remain the same in the solution, indicating that the electrophilicity of Mg2+ affects only the CD3CN molecules directly coordinated to Mg2+. DFT calculations have been performed at the BLYP/6-31+G(2d,p) level to examine the structure and vibrational characteristics of CD3CN coordinated to Mg2+. The calculated results are in good agreement with the observed vibrational characteristics.

No abstract

Fluorine- and chlorine-substituted methyl and methylene radicals have been studied by ab initio quantum chemical methods in order to determine the molecular structure and vibrational frequencies as well as the enthalpies of formation. The equilibrium geometries of radicals have been optimized at various levels, and the vibrational frequencies have been calculated at the optimized geometries. The calculated results, particularly at the MP2/ 6-311G(d) level, are in good agreement with the experimental data reported previously, suggesting that the present levels of theory can yield reasonably accurate estimates for the molecular properties of halogenated radicals when the experimental data are lacking. The standard enthalpies of formation at 298 K, ΔH f°(298 K), of these radicals have been obtained, utilizing the electronic energies calculated by the G2 or the CBS method. Enthalpies of formation for methyl radicals calculated with the original G2 method are close to the experimental values although the claimed accuracy of 2 kcal/mol is not quite achieved, but the errors in enthalpies of formation from other methods are rather high. For methylene radicals whose enthalpies of formation show large discrepancies among the values reported, some assessments have been made based on the calculated enthalpies of formation.

No abstract

Articles you may be interested inProduct vibrational distributions and collision energy dependence of chemiluminescent reactions of group IVA elements with O2, N2O, and NO2 J. Chem. Phys. 92, 4839 (1990); 10.1063/1.457701 Chemiluminescent reactions of ground and metastable states of the group IV A elements with halogensThe chemiluminescent (CL) reactions of group 2 metal elements (Ca, Sr, and Ba) in both the ground and metastable states with various OH-and/or O-containing molecules have been studied in a beam-gas configuration. In reactions with OH-containiiig molecules, it was found that while the ground state atoms produce both the metal oxide and metal hydroxide in excited electronic states, the metastable atoms produce solely metal hydroxide. Also, spectral changes have been observed which can be attributed to changes in the reaction exoergicity or the collision geometry dictated by various scattering gases. Computer simulations of the observed CL spectra have afforded further insight into the potential energy surfaces which govern the reactions.