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@ARTICLE{Kovacevic:42308,
      author       = {Kovacevic, B. and Baric, D. and Maksic, Z. and Müller, T.},
      title        = {{D}ominant {R}ole of the pi {F}ramework in
                      {C}yclobutadiene},
      journal      = {The journal of physical chemistry / A},
      volume       = {108},
      issn         = {1089-5639},
      address      = {Washington, DC},
      publisher    = {Soc.},
      reportid     = {PreJuSER-42308},
      pages        = {9126 - 9133},
      year         = {2004},
      note         = {Record converted from VDB: 12.11.2012},
      abstract     = {The extrinsic antiaromaticity of archetypal cyclobutadiene
                      (CBD) is addressed with particular emphasis on the sigma-pi
                      separability problem. The destabilization energy E(d)(CBD)
                      of CBD is obtained by appropriate homodesmotic reactions
                      involving the open chain zigzag, polyene(s). It is shown
                      that E(d)(CBD) does not depend on the electron correlation
                      and the zero-point vibrational energy contributions, since
                      they are small and of the opposite sign. Consequently, they
                      cancel in the first approximation. Further, it turns out
                      that E(d)(CBD) can be estimated accurately enough with a
                      very modest cc-pVDZ basis set at the Hartree-Fock (HF)
                      level. The extrinsic antiaromatic destabilization
                      E(ean)(CBD) of CBD is deduced after extracting the angular
                      strain energy estimated to be 32 kcal/mol. The resulting
                      E(ean)(CBD) value of 52 kcal/mol is in excellent agreement
                      with the experimental thermodynamic data. If the E(ean)(CBD)
                      is estimated relative to two isolated C=C double bonds, then
                      it assumes 38 kcal/mol, which is roughly 10 kcal/mol per one
                      pi electron. It is, therefore, safe to state that extrinsic
                      antiaromaticity of CBD is larger than its angular strain.
                      Although the sigma and pi electrons are coupled by a mutual
                      Coulomb interaction V-ee(sigmapi), several attempts of their
                      decoupling is made by using three partitioning schemes:
                      stockholder, equipartition, and standard pi-electron theory
                      recipe. The latter allocates the V-nn and V-ee(sigmapi)
                      terms to the sigma- and pi-electron frameworks,
                      respectively. The nuclear repulsion term V-nn is dissected
                      into sigma and pi components in the former two partitioning
                      schemes by using stockholder criterion. It appears that the
                      extrinsic antiaromatic destabilization E(ean)(CBD) is
                      determined by the pi-electron framework according to all
                      three partitioning models.},
      keywords     = {J (WoSType)},
      cin          = {ZAM},
      ddc          = {530},
      cid          = {I:(DE-Juel1)VDB62},
      pnm          = {Betrieb und Weiterentwicklung des Höchstleistungsrechners},
      pid          = {G:(DE-Juel1)FUEK254},
      shelfmark    = {Chemistry, Physical / Physics, Atomic, Molecular $\&$
                      Chemical},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000224538900018},
      doi          = {10.1021/jp0489626},
      url          = {https://juser.fz-juelich.de/record/42308},
}