Electron delocalization in linearly pi-conjugated systems: a concept for quantitative analysis.
Donor- and/or acceptor-substituted pi-conjugated systems represent an important class of compounds in organic chemistry. However, up to now, a general method to quantitatively address the efficiency of a conjugated path is still missing. In this work, a novel computational approach based on deletion energies and on second-order orbital interaction energies in a natural bond orbital (NBO) scheme is employed to quantitatively assess ("measure") delocalization energies. Moreover, the purpose of this work is to assess the efficiency of distinct pi-conjugated paths, that is, geminal, cis, and trans, as well as to predict the impact of substituents on a given backbone. This study is focused on various mono-, di-, tri-, and tetrasubstituted tetraethynylethenes (TEEs). These model systems are suitable for our analysis, because they offer distinct conjugation paths within the same molecule, and can also be substituted in multiple ways. Differences between conjugation paths, the effect of neighbor paths, and the impact of donor and acceptor substituents on the various paths are discussed.
Laboratory of Physical Chemistry, Swiss Federal Institute of Technology, 8093 Zürich, Switzerland.
Maria Grazia
MG
Giuffreda
Maurizio
M
Bruschi
Hans Peter
HP
Lüthi