Aromatic nitrogen compounds

Environmental exposure Atmospheric pollutants, eg, polynuclear aromatic compounds, nitrogen and sulfur oxides Carbonyl compounds by photolysis of hydroperoxides Unsaturation by photolysis of ketones Water Ozone... 

Cyclic compounds that have one or more atoms other than carbon within the ring are called heterocyclic compounds. Those that have 4 + 2 ti electrons are heterocyclic aromatic compounds. Nitrogen and oxygen are the most commonly encountered heteroatoms in naturally occurring heterocyclic compounds. Sidfur-containing aromatic compounds also exist. The structures of a few commonly encountered heterocyclic aromatic compounds are shown below. 

Indole is classified as a 7c-excessive aromatic compound. It is isoelectronic with naphthalene, with the heterocyclic nitrogen atom donating twm of the ten 7t-electrons. 

As is broadly true for aromatic compounds, the a- or benzylic position of alkyl substituents exhibits special reactivity. This includes susceptibility to radical reactions, because of the. stabilization provided the radical intermediates. In indole derivatives, the reactivity of a-substituents towards nucleophilic substitution is greatly enhanced by participation of the indole nitrogen. This effect is strongest at C3, but is also present at C2 and to some extent in the carbocyclic ring. The effect is enhanced by N-deprotonation. 

A large group of heterocyclic aromatic compounds are related to pyrrole by replacement of one of the ring carbons p to nitrogen by a second heteroatom Com pounds of this type are called azoles... 

Two nitrogen containing heterocyclic aromatic compounds—pyrimidine and purine— are the parents of the bases that constitute a key structural unit of nucleic acids... 

In presence of one carbon-nitrogen triple bond —C—C=N In compounds with tendency to dipole formation, e.g., C=C—C=0 In aromatic compounds... 

Ozone ALkenes, aromatic compounds, bromine, diethyl ether, ethylene, HBr, HI, nitric oxide, nitrogen dioxide, rubber, stibine... 

CoF is used for the replacement of hydrogen with fluorine in halocarbons (5) for fluorination of xylylalkanes, used in vapor-phase soldering fluxes (6) formation of dibutyl decalins (7) fluorination of alkynes (8) synthesis of unsaturated or partially fluorinated compounds (9—11) and conversion of aromatic compounds to perfluorocycHc compounds (see Fluorine compounds, organic). CoF rarely causes polymerization of hydrocarbons. CoF is also used for the conversion of metal oxides to higher valency metal fluorides, eg, in the assay of uranium ore (12). It is also used in the manufacture of nitrogen fluoride, NF, from ammonia (13). 

Indole is planar with 10 TT-electrons in a completely conjugated system. The ring is classified as a TT-excessive he tero aromatic compound because of the electron-donating character of the pyrrole-type nitrogen atom. The TT-system is relatively electron-rich, particularly at C-3, as represented by resonance stmcture (lb). 

Coke-oven tar is an extremely complex mixture, the main components of which are aromatic hydrocarbons ranging from the monocyclics benzene and alkylbenzenes to polycycHc compounds containing as many as twenty or more rings. HeterocycHc compounds containing oxygen, nitrogen, and sulfur, but usually only one heteroatom per ring system are present. Small amounts of paraffinic, olefinic, and partly saturated aromatic compounds also occur. 

These are subdivided into (a) compounds isomeric with aromatic compounds in which the ring contains two double bonds but also an hybridized carbon (7 systems Scheme 6) or a quaternary nitrogen atom (9 systems Scheme 7). 

Scheme 7 Isomers of aromatic compounds with a quaternary nitrogen atom ...

Methods of Introduction of Ruonne into Aromatic and Nitrogen-Contaimng Heterocyclic Compounds (Czech ) Hradil, P, Radi, S Chem Listy S4, 952-969 113 ... 

In many cases, however, the ortho isomer is the predominant product, and it is the meta para ratio which is close to the statistical value, in reactions both on benzenoid compounds and on pyri-dine. " There has been no satisfactory explanation of this feature of the reaction. One theory, which lacks verification, is that the radical first forms a complex with the aromatic compound at the position of greatest electron density that this is invariably cither the substituent or the position ortho to the substituent, depending on whether the substituent is electron-attracting or -releasing and that when the preliminary complex collapses to the tr-complex, the new bond is most likely to be formed at the ortho position.For heterocyclic compounds such as pyridine it is possible that the phenyl radical complexes with the nitrogen atom and that a simple electronic reorganization forms the tj-complex at the 2-position. 

The reaction of A-acyliminium ions with nucleophilic carbon atoms (also called cationic x-amidoalkylation) is a highly useful method for the synthesis of both nitrogen heterocycles and open-chain nitrogen compounds. A variety of carbon nucleophiles can be used, such as aromatic compounds, alkcncs, alkyncs, carbcnoids, and carbanions derived from active methylene compounds and organometallics. 

In Figure 22.2, the abundance of the molecular ion at m/z 138 suggests an aromatic compound. Examining the losses from the molecular ion (M-46 and M-30) shows that it is a nitro compound. Because the molecular ion is of even mass, an even number of nitrogen atoms must be present. Looking up m/z 92 in Part III for possible structures, the following is suspected ... 

Griess (1860) coined the prefix diazo for the nitrosation product of an aromatic amine, because he assumed that two nitrogen atoms replaced two hydrogen atoms of the parent aromatic compound. On the other hand, azobenzene received its name on the basis of the C H N ratio 6 5 1, indicating the replacement of one hydrogen by one nitrogen atom. 

The large activating effect of a methyl group upon the reactivity of aromatic quaternary nitrogen compounds noted above has been confirmed by Utley and Vaughan55, who have measured the second-order rate coefficients and the... 

Reaction No. 5 (Table 11) is part of a synthetically useful method for the alkylation of aromatic compounds. At first the aromatic carboxylic acid is reductively alkylated by way of a Birch reduction in the presence of alkyl halides, this is then followed by an eliminative decarboxylation. In reaction No. 9 decarboxylation occurs probably by oxidation at the nitrogen to the radical cation that undergoes decarboxylation (see... 

Ozone-Mediated Nitration of Aromatic Compounds with Lower Oxides of Nitrogen," Mori, T. Srnm Synlett, 1995, 383... 

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