Delocalized electrons bonding

He emphasized that quantum chemistry was built upon many chemical concepts, often inherited from classical chemical theories. K-electrons, L-electrons, valence electrons, 7c- or (7-electrons, localized or delocalized electrons, bonds, and so forth, were certainly incompatible with the quantum mechanical ideas of indistinguishability and nonlocality but had proved to be very useful tools for chemists and had been appropriated by quantum chemists (Daudel 1952). Hence, he argued, they should be given alternative formulations compatible with the new physics. Such was the case of the concept of "loge" introduced by Daudel and his students to explain quantum-... 

The transition state involves six partially delocalized electrons being transformed from one 1,5-diene system to another. The transition state could range in character from a 1,4-diradical to two nearly independent allyl radicals, depending on whether bond making or bond breaking is more advanced. The general framework for understanding the substituent effects is that the reactions are concerted with a relatively late transition state with well-developed C(l)—C(6) bonds. 

The cyclic [SaNs]" cation (5.13), a six r-electron system, is the only example of a nitrogen-rich, binary S-N cation. The thermally stable salt [SaNslaiHgaCle] is obtained from the reaction of (NSC1)3 with HgCla in CHaCla. The bond lengths in the five-membered ring indicate delocalized r-bonding that is attenuated across the S-S bond. 

It may also be represented as a hexagon with a circle in the middle. The circle is a symbol of the n cloud encircling the benzene ring. The delocalized electrons associated with the benzene ring impart very special properties to aromatic hydrocarbons. They have chemical properties of single-bond compounds such as paraffin hydrocarbons and doublebond compounds such as olefins, as well as many properties of their own. 

All atoms taking part in the resonance, that is, covered by delocalized electrons, must lie in a plane or nearly so (see p. 42). This, of course, does not apply to atoms that have the same bonding in all the canonical forms. The reason for planarity is maximum overlap of the p orbitals. 

DELOCALIZED CHEMICAL BONDING orbitals to form the aromatic 10-electron loop. ... 

Keywords Chemical orbital theory, Cw-stability, Cyclic conjugation. Disposition isomers. Diradicals, Donor-acceptor, Electron delocalization, Geminal bond participation, Inorganic heterocycles. Ring strain. Orbital phase. Orbital phase continuity. Polarization, Preferential branching. Reactivity, Selectivity, Stability, Tautomerism, Z-selectivity... 

Oxo-2,5-cyclohexadienylidene [83] was generated in solid argon at 9 K by irradiation of diazo compound [84] with visible light (A>495 nm) (Sander et al., 1988 Bucher and Sander, 1992 Bucher et al., 1992). The IR, UV, and esr spectra of [83] were in accord with a structure having a triplet state with one delocalized electron. In the IR spectrum of the carbene [83] the r (CO) mode was found at 1496 cm which indicates a bond order of the C—O bond considerably less than 2. The low-temperature reaction of carbene [83] with CO generated the keto-ketene [85]. Irradiation (A = 543 10 nm) of [83] led to its transformation into a very labile species, presumed to be [86], which rearranged back to [83] not only under UV or... 

As their names suggest, molecular orbitals can span an entire molecule, while localized bonds cover just two nuclei. Because diatomic molecules contain just two nuclei, the localized view gives the same general result as molecular orbital theoiy. The importance of molecular orbitals and delocalized electrons becomes apparent as we move beyond diatomic molecules in the follow-ing sections of this chapter. Meanwhile, diatomic molecules offer the simplest way to develop the ideas of molecular orbital theory. 

The double bond shown in different locations in the two resonance stmctures represents a pair of electrons in a delocalized n bonding molecular orbital that spans all three of the oxygen atoms, as shown in Figure I0-37a. One lone pair also appears in different positions in the two resonance stmctures, again signaling a delocalized orbital. This lone pair is spread over both outer atoms but not across the inner atom, as shown in Figure I0-37Z>. This is a nonbonding molecular orbital,. The lone pair shown in different positions in the resonance stmctures occupies the delocalized orbital. 

If the molecule contains multiple bonds, construct the n bonding system using molecular orbital theory, as described in this section and in the remaining pages of Chapter 10. Watch for resonance structures, which signal the presence of delocalized electrons. 

Butadiene, used in the chemical industiy as a precursor of synthetic mbber, is a hydrocarbon with the formula C4 Hg. (See Box 13-1 to learn more about the mbber industry.) The Lewis stmcture of butadiene contains two double bonds on sequential pairs of carbon atoms. The chemistry of butadiene, including its ability to form mbber, can be traced to the delocalized electrons in the tt system of the molecule. 

Electron delocalization Electrons in a molecule that are not associated with any particular bond or atom. 

Metallic bonding The bonding present in metallic crystals composed of a lattice of positively charged atoms in a sea of delocalized electrons. 

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