Bonds Transferring Electrons

Ionic bonds tend to form between metals and nonmetals. The metal atoms give up one or more electrons to form positive ions and the nonmetal atoms gain one or more electrons to form negative ions. Common examples of ionic compounds are ones in which the metal is an alkali or alkaline earth element and the nonmetal is ox)rgen, sulfur, or a halogen. 

Consider the ionic compound sodium chloride (NaCl), which consists of a lattice of Na+ and Cl ions that alternate in three dimensions. Even though there are not discreet molecules of NaCl, as there are, for example, with Cl, we can isolate one pair of positive and negative ions and call that a molecule. 

The positive charge on the Na+ ion is there because the ion has one less electron than a neutral Na atom does. The negative charge on the Cl ion is there because the ion has one more electron than a neutral Cl atom does. Opposite charges attract each other. 

The attraction between a positive ion and a negative ion is what chemists call the ionic bond. Ionic bonds tend to be very strong. Because there are so many ionic bonds in a macroscopic-sized crystal and they extend in all three dimensions, ionic compounds can be expected to be hard solids at room temperature. 

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It has generally been concluded that the photoinitiation of polymerization by the transition metal carbonyls/ halide system may occur by three routes (1) electron transfer to an organic halide with rupture of C—Cl bond, (2) electron transfer to a strong-attracting monomer such as C2F4, probably with scission of-bond, and (3) halogen atom transfer from monomer molecule or solvent to a photoexcited metal carbonyl species. Of these, (1) is the most frequently encountered. 

Reduced nicotinamide-adenine dinucleotide (NADH) plays a vital role in the reduction of oxygen in the respiratory chain [139]. The biological activity of NADH and oxidized nicotinamideadenine dinucleotide (NAD ) is based on the ability of the nicotinamide group to undergo reversible oxidation-reduction reactions, where a hydride equivalent transfers between a pyridine nucleus in the coenzymes and a substrate (Scheme 29a). The prototype of the reaction is formulated by a simple process where a hydride equivalent transfers from an allylic position to an unsaturated bond (Scheme 29b). No bonds form between the n bonds where electrons delocalize or where the frontier orbitals localize. The simplified formula can be compared with the ene reaction of propene (Scheme 29c), where a bond forms between the n bonds. 

Strong donor-acceptor interaction shifts the reaction from the pseudoexcitation band to the transfer band. Electrons delocalize from the HOMO of propene to the LUMO of X=Y too much to form a bond between the double bonds. One electron transfers and a radical ion pair forms. The negatively charged X=Y... 

KoperMTM, Voth GA. 1998. A theory for adiabatic bond breaking electron transfer reactions at metal electrodes. Chem Phys Lett 282 100-106. 

Santos E, Schmickler W. 2007a. Catalyzed bond-breaking electron transfer Effect of the separation of the reactant from the electrode. J Electroanal Chem 607 101-106. 

Santos E, Koper MTM, Schmickler W. 2008. Bond-breaking electron transfer of diatomic reactants at metal electrodes. Chem Phys 344 195-201. 

Bilirubin oxidase, 603-606, 621-626 Biomimetic catalysts, 679-686 Bond-breaking electron transfer reactions, 43-44... 

Amouri and coworkers also demonstrated that the nucleophilic reactivity of the exocyclic carbon of Cp Ir(T 4-QM) complex 24 could be utilized to form carbon -carbon bonds with electron-poor alkenes and alkynes serving as electrophiles or cycloaddition partners (Scheme 3.17).29 For example, when complex 24 was treated with the electron-poor methyl propynoate, a new o-quinone methide complex 28 was formed. The authors suggest that the reaction could be initiated by nucleophilic attack of the terminal carbon of the exocyclic methylene group on the terminal carbon of the alkyne, generating a zwitterionic oxo-dienyl intermediate, followed by proton transfer... 

Keywords Anion-n interaction Charge transfer Electronic spectra Halogen n-bonding X-ray crystallography... 

He became interested in a new theory of chemical bonds based on Niels Bohr s 1913 model of the atom, which Thomas Midgley also used to discover tetraethyl lead and CFCs (Chapter 6). Scientists already knew that atoms could form molecules by transferring electrons, but the new theory suggested that chemical bonds could also be formed when atoms share electrons. 

The first coordination sphere is a special case. It can be generated from the trigonal planar arrangement by adding a further ligand, resulting a tin atom which simultaneously acts as an acid and a base. An illustrative example for this kind of bonding is compound 733) in which the tin atom receives electrons from pyridine and transfers electrons to the chromium atom (see also Chapter 6). 

Organometals and metal hydrides as electron donors in addition reactions 245 Oxidative cleavage of carbon-carbon and carbon-hydrogen bonds 253 Electron-transfer activation in cycloaddition reactions 264 Osmylation of arene donors 270... 

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