Divalent atoms

For such purposes as locating substituents, monocyclic heterocycles having only one non-carbon atom are numbered starting with the hetero atom as 1. If there is more than one hetero atom of the same kind, the more saturated hetero atom takes precedence (cf. imidazole in Table 1). In isoxazole and isothiazole, the divalent atom takes precedence, in conformity with the pnaciples of the Hantzsch-Widman system (Section 1.02.2.2). 

It is generally true that a divalent atom with two p orbitals as valence orbitals forms an angular molecule. Since this prediction is reliable, the bonding is usually characterized by identifying the valence orbitals. Oxygen is said to use p5 (read, p two ) bonding in water and FjO. 

We see that each oxygen atom has residual bonding capacity. Each atom could, for example, react with a hydrogen atom to form hydrogen peroxide, as shown in electron dot representation (26). Each oxygen atom could react with a fluorine atom to form F2O2. In short, each oxygen atom is in need of another atom with mi electron in a half-filled valence orbital so that it can act as a divalent atom. 

Tab. 3.6-5. Homometallic cage compounds of the type [M (L)m(REH) (RE)y] of the divalent atoms M [alkaline earth metals and tin(+2)] and the pnictogen atoms E (P, As).

Ferrite. Iron which, in pig iron or steel, has not combined with carbon to form cementite (FeaC). It exists in a, /9, y and 8 forms, which vary in magnetism and ahility to dissolve cementite. Name also applied to compd NaFe02 (called Na ferrite), to ferromagnetic oxides having a definite cryst structure (spinels) and the formula M++Fe ++04 of which the divalent metal may be Fe, Ni, Zn, or Mn. The magnetic props vary accdg to the divalent atom present, and ferrites are now tailored for their desired effect, as Ni-Al ferrite ... 

Note that divalent atoms (oxygen and sulfur) are not counted in the formula. 

Polar structures must be used for compounds containing an atom in a higher valence state, such as sulfur or phosphorus. Thus, if we treat sulfur in dimethyl sulfoxide (DMSO) formally as a divalent atom, the... 

FIGURE 29. Arduengo-type carbenes with divalent atoms E = C, Si, Ge... 

Similarly to the case of the triatomic species (Section III), comparison of absorption maxima of stable germylenes, stannylenes and plumbylenes bearing the same substituents at different divalent atoms of the Group 14 elements (Table 4) does not reveal any... 

Me3C6H)2, E(Si(SiMe3)3)(2,4,6-(CF3)3C6H2), E(NR2)2, E(PR2)2. None of these series is complete. Obviously, the same substituents reveal their effects to a different extent, depending on the nature of the divalent atom. Unfortunately, there are no UV data on labile stannylenes and plumbylenes with relatively simple substituents. 

The first bands in the PE spectra of E(CH(SiMe3)2)2 were assigned to the ionization from the a HOMO, which represents a combination of sp hybrid orbitals of the divalent atom E and the carbon 2p orbitals. This MO is mainly localized on the atom E and has its lone-pair character due to a predominant contribution from s AO. Interaction of the E atom p AO with the E atom s AO lowers the energy of the resulting MO, while the interaction with a-carbon p AOs raises it relative to the energy of the p AO of the free atom E. Both effects approximately balance out, and the resulting IE for ionization from the HOMO of ER2 has been noted to be close to the atomic first IE due to ionization from p AO. 

Thus, the compound C7H7NO has an index of 7 - 3.5 + 0.5 + 1 = 5. Note that divalent atoms (oxygen and sulfur) are not counted in the formula. 

Three classes of palladium salts are known, namely, palladous salts, in which the metal functions as a divalent atom, and palladic salts, in which the metal is trivalent and tetravalent. The palladous salts are stable, but upon ignition yield metallic palladium. 

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