Nitric electrons

Industrially nitrogen monoxide is prepared by the catalytic oxidation of ammonia as an intermediate in the manufacture of nitric acid (p. 238). The molecule of nitrogen monoxide contains an odd number of electrons and can be represented as... 

Silver has little tendency to formally lose more than one electron its chemistry is therefore almost entirely restricted to the + 1 oxidation state. Silver itself is resistant to chemical attack, though aqueous cyanide ion slowly attacks it, as does sulphur or a sulphide (to give black Ag S). hence the tarnishing of silver by the atmosphere or other sulphur-containing materials. It dissolves in concentrated nitric acid to give a solution of silver(I) nitrate. AgNOj. 

A silicon atom might be expected to release electrons inductively, but because of empty 7-orbitals shows the overall character ( + 7 —717). Nitration of trimethylsilylbenzene with nitric acid in acetic anhydride at —10 to o °C gives 25-5,39-8,30-2 and 6-8 %, respectively, of 0-, m-, and /)-nitro-trimethylsilylbenzene and nitrobenzene, with a rate of reaction relative to that of benzene of about 1-5. The figures give no indication of an important conjugative effect. 

Moving now to nitrogen we see that it has four covalent bonds (two single bonds + one double bond) and so its electron count is 5(8) = 4 A neutral nitrogen has five electrons m its valence shell The electron count for nitrogen m nitric acid is one less than that of a neutral nitrogen atom so its formal charge is +1... 

Electron Delocalization in the Conjugate Base With a of —1 4 nitnc acid is almost completely ionized m water If we look at the Lewis structure of nitric acid m light of what we have said about inductive effects we can see why The N atom m nitric acid IS not only electronegative m its own right but bears a formal charge of +1 which enhances its ability to attract electrons away from the —OH group... 

Some heteronuclear diatomic molecules, such as nitric oxide (NO), carbon monoxide (CO) and the short-lived CN molecule, contain atoms which are sufficiently similar that the MOs resemble quite closely those of homonuclear diatomics. In nitric oxide the 15 electrons can be fed into MOs, in the order relevant to O2 and F2, to give the ground configuration... 

In 1973 the Semiconductor Equipment and Materials Institute (SEMI) held its first standards meeting. SEMI standards are voluntary consensus specifications developed by the producers, users, and general interest groups in the semiconductor (qv) industry. Examples of electronic chemicals are glacial acetic acid [64-19-7] acetone [67-64-17, ammonium fluoride [12125-01 -8] and ammonium hydroxide [1336-21 -6] (see Ammonium compounds), dichloromethane [75-09-2] (see Cm.OROCARBONSANDcm.OROHYDROCARBONs), hydrofluoric acid [7664-39-3] (see Eluorine compounds, inorganic), 30% hydrogen peroxide (qv) [7722-84-1] methanol (qv) [67-56-1] nitric acid (qv) [7697-37-2] 2-propanoI [67-63-0] (see Propyl alcohols), sulfuric acid [7664-93-9] tetrachloroethane [127-18-4] toluene (qv) [108-88-3] and xylenes (qv) (see also Electronic materials). 

Oxidizing Properties. Nitric acid is a powerful oxidizing agent (electron acceptor) that reacts violentiy with many organic materials (eg, turpentine, charcoal, and charred sawdust) (19,20). The concentrated acid may react explosively with ethanol (qv). Such oxidizing properties have had military appHcation nitric acid is used with certain organics, eg, furfuryl alcohol and aniline, as rocket propellant (see Explosives AND PROPELLANTS). 

Cobalt(II) nitrate hexahydrate [10026-22-9], Co(N02)2 6H20, is a dark reddish to reddish brown, monoclinic crystalline material containing about 20% cobalt. It has a high solubiUty in water and solutions containing 14 or 15% cobalt are commonly used in commerce. Cobalt nitrate can be prepared by dissolution of the simple oxide or carbonate in nitric acid, but more often it is produced by direct oxidation of the metal with nitric acid. Dissolution of cobalt(III) and mixed valence oxides in nitric acid occurs in the presence of formic acid (5). The ttihydrate forms at 55°C from a melt of the hexahydrate. The nitrate is used in electronics as an additive in nickel—ca dmium batteries (qv), in ceramics (qv), and in the production of vitamin B 2 [68-19-9] (see Vitamins, VITAMIN B22)-... 

Electrophilic substitution reactions of unsubstituted quinoxaline or phenazine are unusual however, in view of the increased resonance possibilities in the transition states leading to the products one would predict that electrophilic substitution should be more facile than with pyrazine itself (c/. the relationship between pyridine and quinoline). In the case of quinoxaline, electron localization calculations (57JCS2521) indicate the highest electron density at positions 5 and 8 and substitution would be expected to occur at these positions. Nitration is only effected under forcing conditions, e.g. with concentrated nitric acid and oleum at 90 °C for 24 hours a 1.5% yield of 5-nitroquinoxaline (19) is obtained. The major product is 5,6-dinitroquinoxaline (20), formed in 24% yield. 

Nilrosated fluoro compounds are frequently prepared by electrophilic nitrosation on an electron-nch center of oxygen, nitrogen, or carbon The preparation of fluorochloronitronitrosomethane from the decarboxylation of fluorochloronitro-acetic acid in nitric acid is unique [f ] (equation 1)... 

FIGURE 1.5 Counting electrons in nitric acid. The electron count of each atom is equal to half the number of electrons it shares in covalent bonds plus the number of electrons in its own unshared pairs. 

Nitric oxide is the simplest thermally stable odd-electron molecule known and, accordingly, its electronic structure and reaction chemistry have been very extensively studied. The compound is an intermediate in the production of nitric acid and is prepared industrially by the catalytic oxidation of ammonia (p. 466). On the laboratory scale it can be synthesized from aqueous solution by the mild reduction of acidified nitrites with iodide or ferrocyanide or by the disproportionation of nitrous acid in the presence of dilute sulfuric acid ... 

The molecular orbital description of the bonding in NO is similar to that in N2 or CO (p. 927) but with an extra electron in one of the tt antibonding orbitals. This effectively reduces the bond order from 3 to 2.5 and accounts for the fact that the interatomic N 0 distance (115 pm) is intermediate between that in the triple-bonded NO+ (106 pm) and values typical of double-bonded NO species ( 120 pm). It also interprets the very low ionization energy of the molecule (9.25 eV, compared with 15.6 eV for N2, 14.0 eV for CO, and 12.1 eV for O2). Similarly, the notable reluctance of NO to dimerize can be related both to the geometrical distribution of the unpaired electron over the entire molecule and to the fact that dimerization to 0=N—N=0 leaves the total bond order unchanged (2 x 2.5 = 5). When NO condenses to a liquid, partial dimerization occurs, the cis-form being more stable than the trans-. The pure liquid is colourless, not blue as sometimes stated blue samples owe their colour to traces of the intensely coloured N2O3.6O ) Crystalline nitric oxide is also colourless (not blue) when pure, ° and X-ray diffraction data are best interpreted in terms of weak association into... 

Nitroxides are iV, iV-disubsdnited nitric oxide radicals, the unpaired electron being delocalized between the nitrogen and oxygen The reduction of 2-methyl-2-nitropropane with sodium or electrochemically yields di-r-butyl nitroxide as the final product " Such nitroxide radicals are important for the snidy of a organic ferromagnet... 

The Dissociation Constant of Nitric Acid. The largest value of K in Table 9 is that for the (HS04) ion. In Fig. 36 there is a gap of more than 0.2 electron-volt below the level of the (H30)1 ion. As is well known, several acids exist which in aqueous solution fall iu the intermediate region between the very weak acids and the recognized strong acids the proton levels of these acids will fall in this gap. The values of K for these acids obtained by different methods seldom show close agreement. Results obtained by various methods were compared in 1946 by Redlich,1 who discussed the difficulties encountered. 

This is 0.22 electron-volt greater than the value of J for nitric acid in water. The relative positions of the proton levels in methanol, using this value, is shown in Fig. 65. 

Although most of the molecules and polyatomic ions referred to in general chemistry follow the octet rule, there are some familiar species that do not. Among these are molecules containing an odd number of valence electrons. Nitric oxide, NO, and nitrogen dioxide, N02, fall in this category ... 

Water-free nitric acid is amphoteric, ie, it acts both as an acid and a base, or better as an electron donor or electron acceptor. This view, already suggested in the early Hantzsch papers, was supported by Walden (Ref 14) and later by Dalmon (Ref 30). Then Usanovich (Ref 25) demonstrated that nitric acid acts as a base with sulfuric acid and as an acid with water. 

Ceric Oxide (Cerium Dioxide, Cerium Oxide, Ceria). CeOj, mw 172.13, white powd, mp ca 2600°, d 7.132g/cc at 23°. Sol in coned sulfuric and nitric acids, insol in dil acids and w. Prepn is by dissolving CeCOj in 16N HNOa contg 3% H202 and then evapg off the nitrate soln followed by thermal decompn. The yield is 97.6% of 99.8% pure Ce02, The oxide is used in optics, electronics, as a diluent in nuclear fuels (as... 

This statement does not mean, however, that the mechanism of diazotization was completely elucidated with that breakthrough. More recently it was possible to test the hypothesis that, in the reaction between the nitrosyl ion and an aromatic amine, a radical cation and the nitric oxide radical (NO ) are first formed by a one-electron transfer from the amine to NO+. Stability considerations imply that such a primary step is feasible, because NO is a stable radical and an aromatic amine will form a radical cation relatively easily, especially if electron-donating substituents are present. As discussed briefly in Section 2.6, Morkovnik et al. (1988) found that the radical cations of 4-dimethylamino- and 4-7V-morpholinoaniline form the corresponding diazonium ions with the nitric oxide radical (Scheme 2-39). 

The nitration of some heterocyclic compounds by nitric acid in sulphuric acid has been studied by Katritzky et al.s0 d and the results are exactly as expected in that electron-supplying substituents in the ring favour reaction on the conjugate acid whereas electron-withdrawing substituents produce reaction on the free base. Rate coefficients and the kinetic parameters for nitration of pyridine derivatives (and some benzene analogues)50 are given in Table 4a. 

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