title: Orbital interactions in selenomethyl-substituted pyridinium ions and carbenium ions with higher electron demand.
abstract: Computational, solution phase, and crystal structure analysis of 2- and 4-organoselenylmethyl-substituted pyridinium ions (10a-c and 11a-c) provides strong evidence for C-Se hyperconjugation (σ(C-Se)-π*) between the C-Se σ-bond and the π-deficient aromatic ring and a through-space interaction (n(Se)-π*) between the selenium p-type lone pair and the π-deficient aromatic ring. There is also a weak anomeric-type interaction (n(Se)-σ*(CC)) involving the selenium p-type lone pair electrons and the polarized CH(2)-C(Ar) σ-bond. NBO analysis of calculated cations with varying electron demand (B3LYP/6-311++G**) show that C-Se hyperconjugation (σ(C-Se)-π*) is the predominant mode of stabilization in the weakly electron-demanding pyridinium ions (10d, 11d, 14, and 15); however, the through-space (n(Se)-π*) interaction becomes more important as the electron demand of the β-Se-substituted carbocation increases. The anomeric interaction (n(Se)-σ*(CC)) is relatively weak in all ions.
authors.affiliation: School of Chemistry and Bio-21 Institute, University of Melbourne, Parkville 3010 Melbourne, Australia.
authors.forename: S Fern
authors.initials: SF
authors.lastname: Lim
authors.forename: Benjamin L
authors.initials: BL
authors.lastname: Harris
authors.forename: Paul
authors.initials: P
authors.lastname: Blanc
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: White
mesh_terms: D002244:Carbon / Q000737:chemistry*; D004583:Electrons; D008958:Models, Molecular; D008968:Molecular Conformation; D011726:Pyridinium Compounds / Q000737:chemistry*; D011789:Quantum Theory; D012643:Selenium / Q000737:chemistry*
chemical_list: D011726:Pyridinium Compounds; D002244:Carbon; D012643:Selenium