科研之友
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摘要
Atomic charges, as measured by Atoms in Molecule (AIM) or Natural Population Analyses (NPA), of the enolate anions of acetaldehyde and crotonaldehyde and of pentadienyl anion and cation show both charge transfer and polarization effects. In general, normal resonance structures and "curved arrow" symbolism give good representations of pi-relectron distributions, but back-polarizations in the sigma-system complicate these electronic structures and can obscure the correspondence to resonance symbols. Twisting a vinyl group to orthogonality disrupts the pi-system, but the vinyl group retains significant charge transfers and polarizations. The role of polarization is also demonstrated by, the effect of external positive and negative charges on the electronic structure of ethylene. The pi-electronic changes again are straightforward but are changed significantly by sigma-polarizations. The polarizability of ethane is about half that of ethylene.
- 出版日期2011-11-17
