@article{HuangSuterEngels1994,
  author    = {Huang, M.-B. and Suter, H. U. and Engels, Bernd},
  title     = {Theoretical Study of the Dimethylamino Radical (CH\(_3\))\(_2\)N and its protonated cation (CH\(_3\))\(_2\)NH\(^+\)},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-59047},
  year      = {1994},
  abstract  = {In the present work the dimethylamino radical ( ( CH\(_3\)) \(_2\)N) and its protonated cation ( ( CH\(_3\))\(_2\)NH\(^+\)) are investigated by means of ab initio methods. The geometries of various conformations of both compounds are obtained with UMP2/6·31 G** calculations, while the hyperfine structure and its dependence on the geometry is studied using the MRD-Cl/B\(_K\) method. The two molecules are compared to study the inftuence of the protonation on geometry and hyperfine structure. The effects of the rotational barriers on the hyperfine structures of (CH\(_3\))\(_2\)N, (CH\(_3\)CH\(_2\))\(_2\)N and ( (CH\(_3\))\(_2\)CH)\(_2\)N will be discussed.},
  subject      = {Organische Chemie},
  language  = {en}
}
@article{EngelsPeyerimhoffSkell1990,
  author    = {Engels, Bernd and Peyerimhoff, S.D. and Skell, P.S.},
  title     = {Theoretical study of the potential energy surface governing the stereochemistry in ClC\(_2\)H\(_4\) reactions},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58851},
  year      = {1990},
  abstract  = {Large-scale multireference configuration interaction calculations in a double·t·type AO basis including polarization functions are carried out for the potential surface of the ClC\(_2\)H\(_4\9 system. The charge distribution for various extreme points of the surface is discussed. The absolute minimum is found for an asymmetric ClC2H4 structure. The symmetrical bridged nuclear conformation is also found to be stable with respect to dissociation into Cl + C\(_2\)H\(_4\)• The activation energy for rotation about the C-C axis is calculated tobe around 18 kJ/mol, which is comparable tothat for the 1,2 migration {around 26 kJ/mol). The stereochemistry is governed by the fact that addition of CI to C\(_2\)H\(_4\) (or dissociation) is a two-step reaction proceeding through a symmetrica1 intermediate. The direct addition pathway possesses a small barrier of about 8 kJ jmol.},
  subject      = {Organische Chemie},
  language  = {en}
}
@article{WortmannSalehEngelsPeyerimhoff1994,
  author    = {Wortmann-Saleh, D. and Engels, Bernd and Peyerimhoff, S. D.},
  title     = {Theoretical Study of the Reaction O(\(^3\)P) + C\(_2\)H\(_4\) and comparison with the \(^3\)CH\(_3\) + C\(_2\)H\(_4\) Reaction},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-59076},
  year      = {1994},
  abstract  = {The minimum energy path for the reaction O(\(^3\)P\(_g\)) + C\(_2\)H\(_4\)(\(^1\)A\(_g\)) has been calculated by optimizing all relevant geometrical parameters along the approach of oxygen to ethene. A barrier of 4.7 kcal/mol in the \(^3\)A"( ... 9a'\(^2\)- 10a'3a") potential energy surface and an energy difference of 14.4 kcal/mol between the product and the fragments is found at the multireference-configuration interaction level. The corresponding values at the lower-level treatment CASSCF are 9 kcal/mol for the barrier and 9 kcal/mol for the depth of the potential; this shows the importance of inclusion of electron correlation. The barrier for CH\(_2\) rotation for the lowestenergy structure (asymmetric OC\(_2\)H\(_4\)) is around 5 kcal/mol. The energy gap to the first excited state \(^3\)A'( ... 9a'l0a'3a'12) is found tobe 3.6 kcal/mol in MRD-CI calculations at the ground-state minimum. Comparison with \(^3\)CH\(_2\) + C\(_2\)H\(_4\) shows that in this system the lowest-energy surface is \(^3\)A', i.e., the state which is the excited state in 0 + C\(_2\)H\(_4\). This difference in energy ordering of \(^3\)A' and \(^3\)A" states results from the fact that the p\(_x\), p\(_y\), p\(_z\) degeneracy of oxygen orbitals is lifted in \(^3\)CH\(_2\)leading to b\(_1\), b\(_2\). and a\(_1\) MOs whereby the lowest b\(_2\) (a") remains doubly occupied; as a consequence, the reaction pattem between the oxygen and \(^3\)CH\(_2\) approach is different, which is also quite apparent in the calculated charge transfer.},
  subject      = {Organische Chemie},
  language  = {en}
}
@article{SchmidtFantuzziKlopfetal.2021,
  author    = {Schmidt, Paul and Fantuzzi, Felipe and Klopf, Jonas and Schr{\"o}der, Niklas B. and Dewhurst, Rian D. and Braunschweig, Holger and Engel, Volker and Engels, Bernd},
  title     = {Twisting versus delocalization in CAAC- and NHC-stabilized boron-based biradicals: the roles of sterics and electronics},
  series = {Chemistry - A European Journal},
  volume    = {27},
  journal   = {Chemistry - A European Journal},
  number    = {16},
  doi       = {10.1002/chem.202004619},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256636},
  pages     = {5160-5170},
  year      = {2021},
  abstract  = {Twisted boron-based biradicals featuring unsaturated C\(_2\)R\(_2\) (R=Et, Me) bridges and stabilization by cyclic (alkyl)(amino)carbenes (CAACs) were recently prepared. These species show remarkable geometrical and electronic differences with respect to their unbridged counterparts. Herein, a thorough computational investigation on the origin of their distinct electrostructural properties is performed. It is shown that steric effects are mostly responsible for the preference for twisted over planar structures. The ground-state multiplicity of the twisted structure is modulated by the σ framework of the bridge, and different R groups lead to distinct multiplicities. In line with the experimental data, a planar structure driven by delocalization effects is observed as global minimum for R=H. The synthetic elusiveness of C\(_2\)R\(_2\)-bridged systems featuring N-heterocyclic carbenes (NHCs) was also investigated. These results could contribute to the engineering of novel main group biradicals.},
  language  = {en}
}