Resonance aromatic amines

Nuclear Magnetic Resonance. The nmr spectmm of aromatic amines shows resonance attributable to the N—H protons and the protons of any A/-alkyl substituents that are present. The N—H protons usually absorb in the 5 3.6—4.7 range. The position of the resonance peak varies with the concentration of the amine and the nature of the solvent employed. In aromatic amines, the resonance associated with N—CH protons occurs near 5 3.0, somewhat further downfield than those in the aliphatic amines. 

The tautomerism of 2- and 3-aminothiophenes was mentioned by Hartough in his review of thiophenes/ but the first definite evidence became available in 1961 when Hoffman and Gronowitz showed conclusively by nuclear magnetic resonance spectroscopy that these compounds both exist in the amino form. In agreement with this finding, 3-aminothiophene generally behaves as an aromatic amine. ... 

Resonance effects are also important in aromatic amines. m-Nitroaniline is a weaker base than aniline, a fact that can be accounted for by the —7 effect of the nitro group. But p-nitroaniline is weaker still, though the —I effect should be less because of the greater distance. We can explain this result by taking into account the canonical form A. Because A contributes to the resonance hybrid, " the electron density of the unshared pair is lower in p-nitroaniline than in m-nitroaniline, where a canonical form such as Ais impossible. The basicity is lower in the para compound for two reasons, both... 

When primary aromatic amines are treated with nitrous acid, diazonium salts are formed. The reaction also occurs with aliphatic primary amines, but aliphatic diazonium ions are extremely unstable, even in solution (see p. 448). Aromatic diazonium ions are more stable, because of the resonance interaction between the nitrogens and the ring ... 

From appraisal of their respective resonance stabilisation, arylnitrenium ions and alkoxynitrenium ions should form with similar facility. On account of the fact that A-acetoxy-A-acetyl arylamines 7 are penultimate carcinogens in the metabolism of aromatic amines, A-acyloxy-A-alkoxyamides 3 were designed to test their potential as DNA-damaging agents. 

Nuclear magnetic resonance spectroscopy for /V-acyloxy-/V-alkoxyamides 13C NMR spectroscopy, 56-58 15N NMR spectroscopy, 58-59 dynamic 1H NMR spectroscopy, 59 Nucleophilic substitution (SN2) reactions, /V-acyloxy-/V-alkoxyamidcs, 70-90 alcoholysis reactions, 89-90 with aromatic amines, HERON reactions, 70-74... 

Prlmaiy aliphatic amines form highly imstable allqrldlazonlum salts (refer to Section 13.6). Primaiy aromatic amines form arenedlazonlum salts which are stable for a short time in solution at low temperatures (273-278 K). The stability of arenedlazonlum Ion Is explained on the basis of resonance. 

Compcired to the aliphatic amines, the aromatic amines have lower values. This lower value indicates that the product of the protonation of aromatic amines is less stable. The decrease in stability is due to a loss in resonance stabilization of the protonated form. 

The lone pair of electrons on the nitrogen atom makes the amines Lewis bases. As Lewis bases, they may behave as nucleophiles. Because aromatic amines are resonance stabilized, they re weaker nucleophiles than alkyl amines. 

Aromatic amines display strong C—N stretching absorption in the 1342-1266 cm1 region. The absorption appears at higher frequencies (shorter wavelengths) than the corresponding absorption of aliphatic amines because the force constant of the C—N bond is increased by resonance with the ring. 

Resonance effects are also important in aromatic amines. m-Nitroaniline is a weaker base than aniline, a fact that can be accounted for by the —I effect of the nitro group, But... 

An important class of cationic dyes, particularly for yellow to bluish-red hues, is derived from Fischer s base by condensation with 4-formyl-substituted anilines, or from Fischer s aldehyde (which may be prepared from Fischer s base via Vilsmeier formylation (B-71MI11205)) and an aromatic amine (Scheme 3). There are many examples of resonating charge dyes of this type which include a variety of aromatic amines and aldehydes. Of heterocyclic interest are the dyes formed by condensation of Fischer s aldehyde with... 

With the exception of 2,5-diaminopyrrole, which exists predominantly in the 2,5-bisiminopyrrolidine form, the C-aminopyrroles possess the structure of normal aromatic amines and this is generally reflected in their chemical properties. The C-aminopyrroles are, however, less basic than one might expect for an aromatic amine and it is evident that 2-aminopyrroles do not form the pyrrolylammonium ions, but are protonated at the 5-position, giving rise to the resonance-stabilized cations, e.g. (475) (68TL4605, 76S51). 

Huttermann J, Ward JF, Myers LS Jr (1971) Electron spin resonance studies of free radicals in irradiated single crystals of 5-methylcytosine. Int J Radiat PhysChem 3 117-129 Huttermann J, Ohlmann J, Schaefer A, Gatzweiler W (1991) The polymorphism of a cytosine anion studied by electron paramagnetic resonance spectroscopy. Int J Radiat Biol 59 1297-1311 Hwang CT, Stumpf CL, Yu Y-Q, Kentamaa HI (1999) Intrinsic acidity and redox properties of the adenine radical cation. Int J Mass Spectrom 182/183 253-259 Ide H, Otsuki N, Nishimoto S, Kagiya T (1985) Photoreduction of thymine glycol sensitized by aromatic amines in aqueous solution. J Chem Soc Perkin Trans 2 1387-1392 Idris Ali KM, Scholes G (1980) Analysis of radiolysis products of aqueous uracil + N20 solutions. J Chem Soc Faraday Trans 176 449-456... 

Amines are weak bases. Alkylamines and ammonia are of comparable basicity, but aromatic amines are much weaker as a result of delocalization of the unshared electron pair on nitrogen to the ortho and para carbons of the aromatic ring. Amides are much weaker bases than amines because of delocalization of the unshared electron pair on nitrogen to the adjacent carbonyl oxygen. Amides are stronger Bronsted acids than amines because of the partial positive charge on the amide nitrogen and resonance in the amidate anion. 

Draw the important contributors to the resonance hybrid for an aromatic amine. 

For independent confirmation of peroxide accumulation in polymers it was necessary to detect the peroxides analytically after the radicals had disappeared. For this purpose we used the folloving technique. The semistable radicals formed in redox reactions of peroxides and aromatic amines have been studied formerly by paramagnetic resonance [34). 

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