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The geometries and relative stabilities of the open, C2v symmetric and closed, D3h symmetric forms of thiozone and its anion, the adiabatic electron affinity of S3 and the energies of the three low-lying excited electronic states of the thiozone anion (Ã 2B2,B̃ 2A1,C̃ 2A2) at the optimized geometry of the X̃ 2B1 ground state are computed employing coupled-cluster [CCSD(T)], second-order multireference perturbation theory (CASPT2), and multireference CI (MRCI and IC-MRCI) methods using large atomic natural orbital basis sets. In addition, the saddle point for the open→closed isomerization on the neutral S3 potential energy surface is being studied. Surprisingly, the calculations do not show the expected underestimation of the experimentally determined electron affinity, in sharp contrast to test calculations on the sulfur atom, the disulfur molecule, and earlier results for ozone. Apart from this, thiozone and its anion behave in many respects qualitatively similar as ozone and O−3, while quantitatively various differences are observed.

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Accurate data for the adiabatic electron affinities of the radicals C2.H', the CH bond dissociation energies and the gas phase acidities of the polyacetylenes C2nH 2 for n = 1-3 have been obtained using the complete active space SCF approach to optimize the geometries and coupled cluster, and for some cases multi-reference configuration interaction and averaged coupled pair functional methods to refine the energies in connection with the polarized basis sets due to Sadlej and the generally contracted atomic natural orbitals basis sets, respectively. Harmonic frequencies have been computed for all species using a density functional theory/Hartree-Fock hybrid approach employing the Becke3LYP functional and the 6-311G** basis set. Our final theoretical predictions for the electron affinities are 2.96 + 0.04, 3.46 + 0.07 and 3.69 + 0-07 eV for C2H', C4H" and (~6 H', respectively. For the CH binding energies and gas phase acidities we predict D O = 131.7 + 1"2, 130-2 + 2-0, and 127-5 + 2"0 kcalmo1-1 and AGacid, 298 = 369-5 + 2"1, 356"3 + 3"6 and 348"7 + 3"6 kcal mol-1 for C2H2, C4H2 and C6H2, respectively. Where available, these data compare very well with experimental results. In addition, the question of the ground state of the Call" radical has been settled. It is of 21-I symmetry, with the 2E § state lying only some 3 kcal mol 1 higher in energy. Hence there is no 'alternation rule' for the ground state of the species C,H" as all of them except C2 H" assume a 217 ground state.

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An indirect method is presented for the detection and characterisation of intermediates that occur during homogeneously catalysed hydrogenations. In combination with parahydrogen as a reactand, this method takes advantage of NMR spectroscopy and zero‐quantum coherence that becomes modified under the Hamiltonian of an intermediate. The method allows the investigation of highly reactive intermediates that are inaccessible for conventional analytical methods. A theoretical framework is presented based on a density matrix description. It is shown that PASADENA (Parahydrogen and Synthesis Allow Dramatically Enhanced Nuclear Alignment) NMR spectra of strongly coupled spin systems (i.e., AB systems) contain structural information of intermediates, even if they cannot be detected directly.

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