In: Physical Chemistry Chemical Physics, 2015, vol. 17, no. 16, p. 10624–10629
The well-studied benzene dimer radical cation, which is prototypical for this class of species, has been reinvestigated computationally. Thereby it turned out that both the σ-hemibonded and the half-shifted sandwich structures of the benzene dimer cation, which had been independently proposed, represent stationary points on the B2PLYP-D potential energy surfaces. However, these structures belong...
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In: Physical Chemistry Chemical Physics, 2013, vol. 16, no. 5, p. 2011–2019
The electronic and vibrational absorption spectra of the radical anion and cation of p-benzoquinone (PBQ) in an Ar matrix between 500 and 40 000 cm⁻¹ are presented and discussed in detail. Of particular interest is the radical cation, which shows very unusual spectroscopic features that can be understood in terms of vibronic coupling between the ground and a very low-lying excited...
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In: Organic Letters, 2013, vol. 15, no. 19, p. 4932–4935
The oxidation potential of thioethers constrained to be near aromatic rings is lowered, due to an antibonding interaction between the p-type sulfur lone pair with the neighboring phenyl π-system which on removal of an electron becomes a new kind of 3-electron S∴π bonding that reveals itself in the photoelectron spectrum and by an electronic transition involving the orbitals participating in...
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In: Journal of the American Chemical Society, 2013, vol. 135, no. 23, p. 8625–8631
Carbocations are crucial intermediates in many chemical reactions; hence, considerable effort has gone into investigating their structures and properties, for example, in superacids, in salts, or in the gas phase. However, studies of the vibrational structure of carbocations are not abundant, because their infrared spectra are difficult to obtain in superacids or salts (where furthermore the...
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In: The Journal of Organic Chemistry, 2013, vol. 78, no. 7, p. 2908–2913
Parent cyclobutenedione 1 was photolyzed and ionized in an Ar matrix at 10K. The bisketene 2 that results in both cases (in the form of its radical cation after ionization) was characterized by its IR spectrum and by high-level quantum chemical calculations. Experiment and theory show that the neutral bisketene has only a single conformation where the two ketene moieties are nearly perpendicular,...
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In: The Journal of Physical Chemistry A, 2012, vol. 117, no. 3, p. 616–625
Stacked dimers of four polycondensed aromatic hydrocarbons, with structures varying from high to reduced symmetries, have been calculated with dispersion-corrected density functional theory. The configurations of the stacked dimers are readily classified by two in-plane displacements and a relative rotation. The potential energy surface in these three coordinates was calculated with rigid...
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In: Physical Chemistry Chemical Physics, 2012, vol. 14, no. 40, p. 13785-13788
The life time of aromatic radical cations is limited by reactions like β-elimination, dimerization, and addition to the solvent. Here we show that the attachment of such a radical cation to the C-terminal end of an α-/3₁₀-helical peptide further reduces its life time by two orders of magnitude. For PPII-helical peptides, such an effect is only observed if the peptide contains an adjacent...
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In: Progress in Theoretical Chemistry and Physics, 2012, vol. 23, p. 25-38
The multideterminental-DFT approach performed to analyze Jahn-Teller (JT) active molecules is described. Extension of this method for the analysis of the adiabatic potential energy surfaces and the multimode JT effect is presented. Conceptually a simple model, based on the analogy between the JT distortion and reaction coordinates gives further information about microscopic origin of the JT...
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In: Journal of Physical Organic Chemistry, 2012, p. -
Variable temperature ¹H NMR spectroscopic studies of 2, 6-di(o-anisyl) anisole show syn and anti atropisomers at low temperature. The barrier for interconverting these isomers by rotation about the aryl-aryl bond, found by fitting the experimental data, is 41.2 kJ/mol.
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In: Tetrahedron Letters, 2011, vol. 53, no. 7, p. 794-799
The aromatic/antiaromatic behavior of the Jahn–Teller (JT) active benzene cation and anion has been investigated using Density Functional Theory (DFT) calculations of Nuclear Independent Chemical Shifts (NICS) and magnetic susceptibility. NICS parameters have been scanned along the Intrinsic Distortion Path (IDP) for the benzene cation showing antiaromaticity which decreases with increasing...
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