Electronic deficit

An ideal (classical) electrostatic capacitor consists of two plane-parallel metal plates having surface areas S and a mutual distance 5, the gap being filled with air or a dielectric layer (the latter variety often is called a film capacitor). When a capacitor is charged (by applying an electrostatic potential difference A / between the two plates), electrical charges +Q m electron deficit) and Q (an efectron excess), which are equal in magnitude but opposite in sign, will accnmulate on the plates. The values of Q are proportional to the potential difference ... 

Clusters derived from metals which have only a few valence electrons can relieve their electron deficit by incorporating atoms inside. This is an option especially for octahedral clusters which are able to enclose a binding electron pair anyway. The interstitial atom usually contributes all of its valence electrons to the electron balance. Nonmetal atoms such as H, B, C, N, and Si as well as metal atoms such as Be, Al, Mn, Fe, Co, and Ir have been found as interstitial atoms. 

Azatriboretidines 70 and 71 (Scheme 36) are stable because the electron deficit is compensated by exo-cyclic dialkylamino groups, but their aromaticity has not been proven.94... 

This enhanced reactivity of fluoromethyl cyanide is undoubtedly due to the inductive effect of the fluorine atom which produces an electron deficit on the carbon atom linked to the nitrogen, and presumably increases still further the polarity of the carbon-nitrogen bond, so that the electron displacements can be pictured as (IX). The increased polarity of the carbon-nitrogen bond will obviously facilitate polar addition of hydrogen chloride and alcohols (or phenols). 

This initial attack of the ozone molecule leads first to the formation of ortho- and para-hydroxylated by-products. These hydroxylated compounds are highly susceptible to further ozonation. The compounds lead to the formation of quinoid and, due to the opening of the aromatic cycle, to the formation of aliphatic products with carbonyl and carboxyl functions. The nucleophilic reaction is found locally on molecular sites showing an electronic deficit and, more frequently, on carbons carrying electron acceptor groups. In summary, the molecular ozone reactions are extremely selective and limited to unsaturated aromatic and aliphatic compounds as well as to specific functional groups. 

The reactivity of carbenes is strongly influenced by the electronic properties of their substituents. If an atom with a lone pair (e.g. O, N, or S) is directly bound to the carbene carbon atom, the electronic deficit at the carbene will be compensated to some extent by electron delocalization, resulting in stabilization of the reactive species. If both substituents are capable of donating electrons into the empty p orbital of the carbene, isolable carbenes, as e.g. diaminocarbenes (Section 2.1.6), can result. The second way in which carbenes can be stabilized consists in complexation. The shape of the molecular orbitals of carbenes enable them to act towards transition metals as a-donors and 71-acceptors. The chemical properties of the resulting complexes will also depend on the electronic properties of the metallic fragment to which the carbene is bound. Particularly relevant for the reactivity of carbene complexes are the ability of the metal to accept a-electrons from the carbene, and its capacity for back-donation into the empty p orbital of the carbene. 

In this section the preparation and uses of heteroatom-substituted carbene complexes L M=C(Xn)R,2 n) (n = 1, 2 X NRj, OR, SR) will be discussed. In these complexes the electron deficit at the carbene carbon atom is compensated both by electron-donation from the lone pairs on the heteroatom and by d-electron backbonding from the metal (Figure 2.1). 

Because hydrogen, alkyl, or aryl groups can compensate only to a limited extent the electron deficit of the carbene carbon atom, it is mainly the metal and its ligands which provide stabilization in this type of carbene complex. For this reason the reactivity of these compounds depends mainly on the nature and oxidation state of the metal and on the electronic properties of the remaining ligands. 

There are a number of heteroatoms that can substitute for either boron or carbon in the carboranes. The groups that are as electron-deficient as BH groups are listed vertically to the left of the center line in Table V, whereas those that are as capable as carbon in donating electrons are listed to the right of the center line. The transition elements for the most part electronically substitute for boron and occupy high-coordination sites, but upon electron demand the transition element may also substitute for carbon and concomitantly occupy low-coordination sites. Several transition element moieties, by contrast, are one more electron deficient than boron and occupy, as would be anticipated, high-coordination positions and require additional electron donors (CH groups) to counter the electronic deficit (XIII-24). 

Nucleophilic reaction — The nucleophilic reaction is found locally on molecular sites showing electronic deficits and, more frequently, on carbons carrying electron-withdrawing groups. The molecular ozone reactions are extremely selective and limited to unsaturated aromatic and aliphatic compounds, as well as to specific functional groups. 

In Section 5.3.7.3 the formation of a-halogen carbanions and their alkylation was discussed. If these or related intermediates are left to warm, a-elimination will usually occur to yield carbenes, which either react with the solvent, dimerize, or undergo inter- or intramolecular C-H or C-C bond insertion [291, 292, 309, 436], Because of the electron deficit at the carbene carbon atom (six valence electrons only), these intermediates are highly energetic, and their formation by a-elimination is therefore much slower than the formation of alkenes by /3-elimination. 

We have already seen that the one-electron deficit in the corresponding carbonium-sulfonium structures of the 1,2-dithiolium ion (1) (Section II, B, 1) is distributed over two equivalent carbonium structures. The electrophilic character of these two equivalent C-3 and C-5 positions should therefore be weaker than that of C-2 in 2, in spite of the fact that C-2 is flanked by two sulfur atoms which tend to reduce the charge. 

Then Ugi and coworkers, reasoning that the Ti-electron deficit of pentazole could be compensated by electron-donating substituents, were able to obtain crystalline 4-alkoxyphenyl- and 4-dialkylaminophenyl-pentazoles that did not decompose at room temperature. They showed also that the decomposition rate of phenylpentazole at 0 °C slows down according to the increasing solvent polarity (57CB2914, 58CB531, 58CB2324). 

Because of the high electron deficit at the two-coordinate phosphorus atom, phosphenium cations are only stable with electron-donating substituents R, predominantly with nitrogen donor atoms. This is an obvious parallel to the situation with stable carbenes of the Wanzlick-Arduengo type. Therefore most complexes in this series are derived from diazaphospholes (75a,... 

The successful generation, by precipitation out of liquid anhydrous HF, of fluorides thermodynamically unstable with respect to loss of elemental F2, gave a forceful reminder of the remarkable stability of that solvent towards oxidation. Soon after the preparation of AgFa, in attempts to find evidence for cationic derivatives (e.g. [AgF2] ), it was discovered (see Ref. 98) that even divalent silver, as a cation, Ag + (solvated by HF), had the capability to oxidize Xe. This made chemical sense, since a cation, having an electron deficit, should have higher electronegativity than a related oxidation-state in a neutral or anionic species. Indeed, this had three important consequences. 

Example A small amount of In (Group 13) added to Si (Group 14) Valence electron deficit is created in the previously full valence band of Si, thereby becoming a conduction band. 

Red flavylium cations have an electron deficit. The six limit formulae possible, according to the position of the (+) charge, are all in equilibrium ... 

No-bond resonance. An extension of traditional resonance structure formulations wherein one violates the octet rule with a two-electron deficit being placed on an alkyl group to explain the electron-donating nature of alkyl groups. 

The second column consists of halide-substituted carbene complexes [14]. In these cases, the bonding scheme is similar to Fischer carbenes in that the singlet halocarbene fragments interact with singlet metal centers, but the halide substituents do not contribute as much electron density into the carbon p orbital as the more strongly jt-donating alkoxide substituents. Presumably, this electronic deficit... 

If these impurities have an electronic deficit compared to the lattice element, then electronic acceptor levels Ea are assigned to them. 

With regard to the urethane group formation, Kozak et al [90] concluded that the electronic deficit at the NCO carbon is not a sufficient condition to promote the... 

---