Neutral resonance structure, bond length

Figure 3.7. Definition of regions from A to E of bond length alternation with the percentage contribution of neutral (structure I) and charge separated (structure II) resonance structures to the ground state. This pattern demonstrates the evolution of the charge separated structure from the neutral from passing through polar structure with almost equal bond lengths (region C). (From Ref. [319] with permission of the American Association for the Advancement of Science.)...

Fig. 1.10 Left. Canonical resonance structures for the l-dimethylamino-l,3,5,7-octatetraen-8-al molecule, DAO. (Top) Neutral polyene limit (middle) cyanine limit (bottom) zwitterionic charge-separated limit. Right Corresponding evolution of bond length alternation BLA (in A) (x) and bond order alternation BOA ( ), as a function of the applied external electric field F.

With trivatent metals, acetylacetone thus forms neutral tns complexes such as [Al(acac)3, [Tifacac),], (Crfacac),], and [Cofacac),]. As a result of resonance, the two M—O bonds in each of these complexes are equal in length, as are the two C—O and the two ring C—C bonds, giving a symmetric structure (only one ring shown) ... 

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