TY - JOUR
T1 - New interpretation of the valence tautomerism of 1,6-methano[10]annulenes and its application to fullerene derivatives
AU - Choi, Cheol Ho
AU - Kertesz, Miklos
PY - 1998/5/7
Y1 - 1998/5/7
N2 - Relaxed potential energy surface scans of 1,6-methano[10]annulene and its derivatives have been calculated using Hartree-Fock (HF), density functional (DFT), and second-order Møller-Plesset perturbation theory (MP2) in the pursuit of nonclassical structures corresponding to an extremely long C1-C6 bond (∼1.8 Å). Substituents affect the relative stabilities between the aromatic and the bisnorcaradine forms, but their effects on the minima positions are moderate. We attribute the absence of a static C-C bond length in the vicinity of 1.8 Å to the well-defined inherent minima of cyclopropane in its singlet state (∼1.5 Å) and trimethylene in its triplet state (∼2.6 Å), which serve as the basis of our fragment analysis. The 1,6 bonding in these molecules is associated with a shallow potential well, in agreement with the Woodward-Hoffmann rules rather than to the existence of a static intermediate structure with a very long C-C bond. These results are in qualitative agreement with recent temperature-dependent 13C NMR experiments of Dorn et al. The trends in the C1-C6 bridgehead bonding are well-reproduced by the correlated calculations and to a lesser extent even by the HF calculations. However, simple electron donation/withdrawal arguments fail for this series. Due to the similarity in the delocalization energy of 1,6-methano[10]annulenes and disubstituted methanobuckyballs predictions are made concerning the structural preferences for some disubstituted methanofullerenes and -fulleroids. In contrast to general expectations open [6,6] methanofullerenes may exist. Major differences between methano[10]annulenes and methanofullerenes are derived from the constraints concerning the bookfolding angle that are strong in the latter and moderate in the former.
AB - Relaxed potential energy surface scans of 1,6-methano[10]annulene and its derivatives have been calculated using Hartree-Fock (HF), density functional (DFT), and second-order Møller-Plesset perturbation theory (MP2) in the pursuit of nonclassical structures corresponding to an extremely long C1-C6 bond (∼1.8 Å). Substituents affect the relative stabilities between the aromatic and the bisnorcaradine forms, but their effects on the minima positions are moderate. We attribute the absence of a static C-C bond length in the vicinity of 1.8 Å to the well-defined inherent minima of cyclopropane in its singlet state (∼1.5 Å) and trimethylene in its triplet state (∼2.6 Å), which serve as the basis of our fragment analysis. The 1,6 bonding in these molecules is associated with a shallow potential well, in agreement with the Woodward-Hoffmann rules rather than to the existence of a static intermediate structure with a very long C-C bond. These results are in qualitative agreement with recent temperature-dependent 13C NMR experiments of Dorn et al. The trends in the C1-C6 bridgehead bonding are well-reproduced by the correlated calculations and to a lesser extent even by the HF calculations. However, simple electron donation/withdrawal arguments fail for this series. Due to the similarity in the delocalization energy of 1,6-methano[10]annulenes and disubstituted methanobuckyballs predictions are made concerning the structural preferences for some disubstituted methanofullerenes and -fulleroids. In contrast to general expectations open [6,6] methanofullerenes may exist. Major differences between methano[10]annulenes and methanofullerenes are derived from the constraints concerning the bookfolding angle that are strong in the latter and moderate in the former.
UR - http://www.scopus.com/inward/record.url?scp=0007164999&partnerID=8YFLogxK
U2 - 10.1021/jp980773y
DO - 10.1021/jp980773y
M3 - Article
AN - SCOPUS:0007164999
SN - 1089-5639
VL - 102
SP - 3429
EP - 3437
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 19
ER -