Inverted Hyperconjugation in Symmetrical 1,4‐Dihalocubanes
作者:
Evi Honegger,
Edgar Heilbronner,
Thomas Urbanek,
Hans‐Dieter Martin,
期刊:
Helvetica Chimica Acta
(WILEY Available online 1985)
卷期:
Volume 68,
issue 1
页码: 23-38
ISSN:0018-019X
年代: 1985
DOI:10.1002/hlca.19850680104
出版商: WILEY‐VCH Verlag GmbH
数据来源: WILEY
摘要:
AbstractThe σ‐orbital manifold of cubane1, as suggested by its PE spectrum, is divided into two sets separated by a 3 eV gap extending from ∼ ‐10.5 eV to ∼ ‐13.5 eV. Halogen substituents with np AO basis energies falling into this gap (e.g.Cl or Br) will, therefore, hyperconjugate appreciably with both sets. Interaction with the lower‐lying set will lead to the usual destabilization (‘normal’ hyperconjugation), whereas interaction with the set above will necessarily lead to a ‘stabilization’ (‘inverted’ hyperconjugation). As a result the lone‐pair ionization energies of Cl or Br substituted cubanes (derived from PE spectra) are much larger than naively expected for an alkyl halide containing as much as 8 C‐atoms. In particular no significant shift of the e g−1lone‐pair bands in the PE spectra of 1,4‐dichloro‐ and 1,4‐dibromocubane can be detected with respect to the first ionization energies of the
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