Resonant ionic bonding

Whether a carbon-metal bond is ionic or polar-covalent is determined chiefly by the electronegativity of the metal and the structure of the organic part of the molecule. Ionic bonds become more likely as the negative charge on the metalbearing carbon is decreased by resonance or field effects. Thus the sodium salt of acetoacetic ester has a more ionic carbon-sodium bond than methylsodium. 

The first represents a hypothetical HC1 molecule with a purely covalent bond in which the two bonding electrons are equally shared between the two atoms, and the second a hypothetical molecule with a purely ionic bond in which both the bonding electrons have been transferred to the chlorine atom. In this case the two resonance structures do not necessarily... 

The NRT resonance weights, bond orders, and valencies are generally comparable to those of the older Pauling-Wheland theory (particularly for species of low ionicity) and can be used to rationalize chemical phenomena in a similar fashion. Pauling s classic, The Nature of the Chemical Bond, brilliantly illustrates such reasoning. 

D—Ionic bonding needs a metal and a nonmetal (usually). Only the acetate ion has resonating bonds (a and Jt). 

Partial covalency in essentially ionic bonds changes somewhat the distribution of electrons, detectable as electron delocalisation by the modem methods of nuclear magnetic and electron spin resonance (NMR and ESR). Although the interpretations of these measurements widely differ (see 292, 293, 320) they doubtless prove the existence of partial covalency (in the order of magnitude of 10%) even in the most ionic fluorides AMeFg. Little work seems to have been done one fluorides of the heavier transition elements (96), but there is an abundant literature on first transition series fluorides, of which an arbitrary selection is given below for further information. ... 

The molecular complex formed by the interaction of donor and acceptor can be considered as a resonance hybrid of two structures one a no-bond structure (DA) in which the two molecules are bound together only by van der Waals forces and the other in which an ionic bond exists between the donor and the acceptor (D+ — A ). The main contribution to the ground state is from the no-bond structure and the wave function is represented as... 

Instead of using this description of the bond as involving resonance between an extreme covalent bond H C1 and an extreme ionic bond H+Cl-, we may describe the bond as a covalent bond with partial ionic character, and make use of the valence line, writing H—Cl (or H—Cl )... 

Transitions between other extreme types of bonds (covalent to metallic covalent to ion-dipole, etc.) can also occur without discontinuity, and the bonds of intermediate character can be discussed in terms of resonance between structures of extreme type in the same way as for covalent-ionic bonds. 

Resonance is possible, of course, between an ionic FeX structure, with ionic bonds between the Fe+ hf ion and surrounding anions, and a covalent structure in which only the outer orbitals 4s, 4p, 4d, and so on are used in bond formation. This covalent structure writh five unpaired electrons would be different in character from that using two 3d orbitals, however, and continuous transition to the latter could not occur. 

The formation of some organic hydroperoxides by oxidation with molecular oxygen is catalytically promoted by metals like silver or copper 171). A dissociative chemisorption of oxygen cannot be active in these processes they probably proceed via the chemisorption of O7 ions (or O2 molecules forming a covalent bond resonating with an ionic bond). 

The alkyl metals cover nearly the entire spectrum from covalent to ionic bonding so that a choice can be made based on the requirements for each particular monomer and the type of stereoregulaiity desired. Of course, after the first monomer addition, the ionic character of the polymer-metal bond becomes most important. The extent of ionization will depend upon the ionization potential of the metal, resonance stabilization of the anion, and solvation of the cation. The first two are... 

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