LCBO

It is possible in principle to deduce from the position of the first absorption band the twisting angle between the double bonds in cyclic conjugated polyenes, e.g. on the basis of a simple LCBO model50. This has been attempted for cycloocta-l,3,5-triene 184257 and cyclooctatetraene 239260. For the former it was deduced that the --system becomes... 

No. Chemical Log K , MW LCbo (mg/L) Observed Logics,) (mol/L) Predicted Log(LC50) (mol/L) Residual (Observed -Predicted)... 

Finally, the molecular orbitals q>i themselves can be expressed as linear combinations of the bond orbitals a>j (LCBO method) ... 

The fraction of positive charge cfj on the jtb bond is expected to be correlated with the fragmentation of the ion in mass spectroscopy experiments 35,36) other LCBO methods following the same lines have occasionally been used (see e.g. 21>). 

Silyl-substituted acetylenes. The hyperconjugative interaction between the C=C moiety and SiH3 as well as CH3 groups of local C3v symmetry has been discussed extensively as one of the best examples of how to parametrize LCBO-MO models by PE spectroscopic M e state energies (Section IV.E). The ionization patterns of the following mono- and disilyl acetylene derivatives are also reported in the literature153 (cf. Table 62). 

From = 1 in the simple LCBO approach, it follows that... 

Using 73-76,78,81-84,91 and 94 as models it has been shown that the first PE bands can be reproduced very well by a LCBO model. In the case of73-76 and 91-94 the diagonal terms are = nJYLIn = -10.1 eV and = (Ttt/H/TTt) = -11.4 eV, where stands for a double bond and for a triple bond. The higher value for as compared to indicates that the Tt-electrons of the triple bond are more localized than the double bond. 

We place COT in the xy plane and allow it to relax to its stable tub conformation. Atoms 1, 2, 5 and 6 move to positive z and 3, 4, 7 and 8 to negative z, behind the plane of the diagram, but the four tt bonds can still be thought of essentially as being linear combinations of their Pz AOs. The four linear combinations of bond orbitals (LCBOs), labeled by their irreps in D2rf, are ... 

Cubane has cubic (Oj symmetry, but a slight elongation of the four a bonds emphasized in the digram, desymmetrizes the molecule to The four LCBOs are characterized as follows ... 

The characterization of the MOs of the interacting CBD molecules is straightforward. So is that of the two linear combinations of bond orbitals (LCBOs) of cubane, labeled and cr those labeled and (j+ are inter-... 

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