Structural hybrids stmctures

Trivalent ( classical ) carbenium ions contain an, vp2-hybridized electron-deficient carbon center that tends to be planar in the absence of constraining skeletal rigidity or steric interference. (It should be noted that ip-hybridized, linear acyl cations and vinyl cations also show substantial electron deficiency on carbon.) The carbenium carbon contains six valence electrons, and thus it is highly electron-deficient. The stmcture of trivalent carbocations can always be adequately described by using two-electron, two-center bonds (Lewis valence bond structures). 

Sometimes more than one Lewis stmcture can be written and there is no reason to select one over another— all of the structures must be used to represent the substance correctly. The true structure is said to be a resonance hybrid of those Lewis structures. 

Finally, structural characterization of hybrid materials must be refined in many cases, it is unclear where the organic component is located within the overall meso-stmcture of the material. Coupled with experimental data, simulations of the self-assembly process in hybrid materials79 should yield greater insight into the local structure of hybrid precursors. 

Last, ReOs has the octahedral framework of the SrTiOs structure minus the 12-coordinate atom in the center of the unit cell. However, the orbitals on this atom ate of such high energy (Sr electron configuration = 4s 4p 5s ) that they do not hybridize with the Ti 3d-02p bands. In the perovskite stmcture, this atom simply provides electrons to the system that can occupy the valence or conduction bands. Hence, there is little change to the band dispersion directly resulting from the presence of the A cation. 

No resonance structures ean be drawn for 1,4-pentadiene, but three can be drawn for (3 )-l,3-pentadiene (or any other eonjugated diene). The hybrid of these resonance stmctures illustrates that the two adjacent n bonds are delocalized in a conjugated diene, making it lower in energy than an isolated diene. 

As the number of fused benzene rings increases, the number of resonance structures increases as well. Although two resonance stmctures can be drawn for benzene, naphthalene is a hybrid of three resonance structures. 

Problem 10.14 (a) Draw three resonance structures for naphthalene, (b) Which stmcture makes the major contribution to the structure of the hybrid in that it has the smallest energy (c) There are four kinds of C-to-C bonds in naphthalene C -C, C -C, C -C, and C -C . Select the shortest bond and account for your choice. -4... 

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