Bond , covalent delocalized double

The total bond energy of a substance for which resonance structures are written is greater than would be expected if there were only one formal Lewis structure. This additional stabilization is called resonance energy. It arises from the same principle that is responsible for covalent bond energy, the delocalization of electrons about the atoms forming the bond. As a result of resonance in ozone, for example, the electrons constituting the second pair of the double bond are delocalized around the 3... 

Resonance attempts to correct a fundamental defect in Lewis formulas. Lewis formulas show electrons as being localized they either are shared between two atoms in a covalent bond or are unshared electrons belonging to a single atom. In reality, electrons distribute themselves in the way that leads to their most stable arrangement. This sometimes means that a pair of electrons is delocalized, or shared by several nuclei. What we try to show by the resonance description of ozone is the delocalization of the lone-pair electrons of one oxygen and the electrons in the double bond over the three atoms of the molecule. Organic chemists often use curved arrows to show this electron... 

Coordination Compounds with Transition Metals Coordination compounds formally do not count among the covalently bound structures. Still they shall be discussed in this chapter as, compared to other noncovalent variants, they are rather related to the covalently modified nanotubes. One can presume that nanotubes like fullerenes form coordination compounds with transition metals. Yet the tendency to do so is much less pronounced which is, among other reasons, due to the lack of five-membered rings. Hence, firstly, the delocalization of double bonds is less disturbed and, secondly, the energy gap between HOMO and LUMO is wider. The latter effect hinders an efficient backbonding and thus decreases the affinity of the nanotubes toward electron-rich metal systems. The cyclopenta-dienyl units as existent in fullerenes can stabilize the complexes once they come into being, whereas their absence in nanotubes hampers the formation of T -complexes. 

Polymeric methoxides of lithium and sodium are known to adopt a two-dimensional layer structure. Each metal atom is coordinated to four oxygen atoms. A different polymeric, double layer structure is found for KOMe. Both potassium and oxygen atoms form two sheets and the methyl groups lie above and below these sheets. The potassium atoms are pentacoordinate and the oxygen atoms hexacoordinate (5K - - 1C). Since the MeO" ligand has only three lone pairs a delocalized form of covalent bonding, characteristic of an electron deficient structure, must be envisaged. 

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