Home

About

Advanced Search

Browse by Discipline

Scientific Societies

E-print Alerts

Add E-prints

E-print Network
FAQHELPSITE MAPCONTACT US


  Advanced Search  

 
Effect of Double-Hyperconjugation on the Apparent Donor Ability of -Bonds: Insights from the Relative Stability of -Substituted
 

Summary: Effect of Double-Hyperconjugation on the Apparent Donor Ability
of -Bonds: Insights from the Relative Stability of -Substituted
Cyclohexyl Cations
Igor V. Alabugin* and Mariappan Manoharan
Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390
alabugin@chem.fsu.edu
Received September 27, 2004
A combination of electronic, structural, and energetic analyses shows that a somewhat larger
intrinsic donor ability of the C-H bonds compared to that of C-C bonds can be overshadowed by
cooperative hyperconjugative interactions with participation of remote substituents (double
hyperconjugation or through-bond interaction). The importance of double hyperconjugation was
investigated computationally using two independent criteria: (a) relative total energies and
geometries of two conformers ("hyperconjomers") of -substituted cyclohexyl cations (b) and natural
bond orbital (NBO) analysis of electronic structure and orbital interactions in these molecules.
Both criteria clearly show that the apparent donor ability of C-C bonds can vary over a wide range,
and the relative order of donor ability of C-H and C-C bonds can be easily inverted depending on
molecular connectivity and environment. In general, relative donor abilities of bonds can be
changed by their through-bond communication with remote substituents and by greater polariz-
ability of C-X bonds toward heavier elements. These computational results can be confirmed by
experimental studies of conformational equilibrium of -substituted cyclohexyl cations.

  

Source: Alabugin, Igor - Department of Chemistry and Biochemistry, Florida State University

 

Collections: Chemistry; Biology and Medicine