40698-00-8Relevant articles and documents
Long-Range σ-π Interactions in Tetrahydro-4H-thiopyran End-Capped Oligo(cyclohexylidenes). Photo-Electron Spectroscopy, ab Initio SCF MO Calculations, and Natural Bond Orbital Analyses
Marsman, Albert W.,Havenith, Remco W. A.,Bethke, Sabine,Jenneskens, Leonardus W.,Gleiter, Rolf,Van Lenthe, Joop H.,Lutz, Martin,Spek, Anthony L.
, p. 4584 - 4592 (2007/10/03)
Long-range σ-π interactions in tetrahydro-4H-thiopyran end-capped oligo(cyclohexylidenes) were identified by He(I) photoelectron spectroscopy (PES) and ab initio RHF/6-31G* calculations. The vertical ionization energies Iv,j of the highest occupied molecular orbitals (MO's) were assigned using Koopmans' theorem (Iv,j = -∈j) and by correlation with the ionizations of related reference compounds. The experimental (PES) and theoretical (RHF/6-31G*) results are in good agreement. For tercyclohexylidene derivatives which contain two nonconjugated π-bonds splittings ΔIv,j of the π-bands in the range from ～0.5 to 0.7 eV (Δ-∈ ～0.6 to 0.9 eV). For the bi- and tercyclohexylidene compounds containing two sulfur atoms at their α- and ω-end positions the π-type sulfur lone pair bands [Lpπ(S)] split significantly by ΔIv,j ～0.3 to 0.4 eV (Δ-∈j ～0.3 to 0.4 eV), i.e. σ-π interactions over distances of ca. 8 and 12 A, respectively, occur. The magnitude of the interactions and the observed splittings are independent of the anti and syn conformations of the oligo(cyclohexylidene) hydrocarbon skeletons. RHF/6-31G* Natural Bond Orbital analyses reveal that the Hax-C-C-Hax precanonical MO's (PCMO's) centered on the cyclohexyl-type rings are paramount for the relay of the through-bond σ-π interactions; no through-space σ-π interactions were identified.
