BI 1 structure

Stereochemically, even more interesting are the bis-l,3-oxathiane derivatives 98 and 99 <2005STC369>. All compounds are chiral and the chiral elements are carbons C-2/C-2 and the 1,3-oxathine moieties themselves (Equation 9). Due to the bis-structure, compounds 98 and 99 exhibit both homochiral iZR,2 R ZS,Z S) and hetero-chiral (2R,Z S) isomers (Scheme 4) and they reveal rapid equilibration in solution via open-chain intermediates, thereby preventing separation and individual analysis of the isomers in solution. In the solid state, the compounds crystallized either as unique heterochiral isomers or as a mixture of the two as a solid solution. 

For inverse photoemission, similar arguments lead to the interpretation of BIS structures by an analogous Z - 1, v - 1 approximation. 

To confirm that 5 has the expected 1,2-bis structure, we hydrolyzed and oxidized it to the bis-phosphonic acid. The 31p NMR spectra of this acid shows two doublets consistent for a 1,2-bis structure. The - P-NMR spectra reported for the 1,3-bis-(phosphonic acid) propane is a singlet. . 

Fig. 36. The dependence of the order n in the Si(lOO) 2xn-Bi structure as a function of annealing temperature [93P3],...

The first two structures are famous Kekule structures, the next three are Dewar structures, the sixth is an example of the possible mixed covalent-ionic structures. From these graphs, we may deduce which atomic orbitals (out of the 2p, orbital of carbon atoms, z is perpendicular to the plane of the benzene ring) takes part in the covalent bond (of the tt type). As far as the mathematical form of the Heitler-London functions (involving the proper pairs oflpz carbon atomic orbitals), the first for electrons 1,2, the second for electrons 3,4, and the third for 5,6. Within the functions d>/, the ionic structures can... 

The evolution of the spectra is presented as a function of which is varied between -3eV and 12eV. For large positive Cf only one structure, located at Ef and corresponding to the BIS 4f final state is visible. With decreasing Ef, the BIS structure approaches p while a second BIS structure emerges, representing... 

Fig. 33,5. The anti-Th3P4 or Gd Bis structure. Large spheres Bi, small spheres Gd. The coordination polyhedra [GdBij] and [BiGde] are emphasized on the right part. On the left the additional Gd-3Gd contacts are indicated by dotted lines for each of the two distinguishable Gd sublattices.

Bg" " The C2V Bi structure 8.1 is indicated to be the most stable isomer for Bg in many previous reports [36, 38-40]. Other electronic state (C2V A2> was reported by Kato et al. [34] at the MP4(SDTQ)/3-21G level. Interestingly, our calculations at the full CCSD(T)/aug-cc-pVTZ level showed that both electronic states are located having nearly the same energy content. Consequently, 8.1 is the most stable isomer of Bg" " in both electronic states Bi and that are apparently the two stabilized states by a Jahn-TeUer distortion of a higher symmetry form. 

---