Ring heterocyclic

Benzo-fusion to a heterocyclic ring involved in tautomerism has the effect of steering the equilibrium in directions which tend to retain the full aromaticity of the benzene ring. 

The heterocyclic rings in quinoline (116) and isoquinoline are selectively reduced by Pd on carbon-catalyzed reaction of ammonium formatc[107]. Some benzene rings are also reduced. For example, nitrobenzene is reduced to cyclohexylamine (117) with formic acid. It is important to use a sevenfold excess of formic acid[108]. 

All compounds of this heterocyclic ring system so far found in nature are derivatives of pterin (2) and lumazine (3) carrying different substituents in the 6- and/or 7-positions. The most common representatives of these series are listed in Tables 8 and 9. 

Y = 6-membered N-contg. heterocyclic ring having at least one active halo and n = 0 or I. 

Y = 6-membered N-conig. heterocyclic ring which may be Hie dyestuffs arc of formulae (V) or (VI)  

Transformations from Other Heterocyclic Ring Systems 

The shapes of heterocyclic rings are very much like those of their all carbon analogs Thus six membered heterocycles such as piperidine exist m a chair conforma tion analogous to cyclohexane 

Table 2 H Chemical Shifts of Protons on the Heterocyclic Rings of Simple Benzazines cf. naphthalene, column 1)

Ediyleneimine (a2indine, a2acyclopropane) is the smallest cyclic itnine consisting of a three-membered A/-heterocyclic ring (n = 2)  

There is a large variety of chloro or fluoro substituted heterocyclic rings which undergo X displacement by cell-0. Vinyl sulfones are usually generated under alkaline conditions from P-sulfatoethjisulfones, 

The nature of the substituent on the exocyclic nitrogen also influences the ambident activity of anion 48 in DMF (Scheme 35) when R is an heterocyclic ring, nitrogen alkylation predominates (189) when R is a methylamino group, a mixture of the two isomers is reported (190) when 

It is interesting to compare the dimensions of the monocyclic systems with those recorded for their dibenzo counterparts where the aromatic nature of the heterocyclic ring is expected to be much diminished. Comparison of the data in Table 4 with that in Table 2 shows that 

Fluorine and phosphorus occasionally appear attached to, or as part of, heterocyclic rings. However, very little systematic attention has been paid to them, in the area of the azines, 

Not all cyclic compounds are hydrocarbons Many substances include an atom other than carbon called a heteroatom (Section 1 7) as part of a ring A ring that contains at least one heteroatom is called a heterocycle, and a substance based on a heterocyclic ring is 

The reactions of haloquinoxalines in which the halogen atom is bonded to the benzenoid ring have not been well studied, but by analogy with examples in the phenazine series it would seem probable that they are unlikely to be displaced with the same ease as those bonded directly to the heterocyclic ring. It is evident from the foregoing discussion that A-oxidation has a pronounced effect on their reactivity, and, by this means, considerable latitude in the specific functionalization of dihalo or polyhalo derivatives may be exercised. 

Hydrazino groups are also converted into H-compounds with mercury(II) oxide (74CR(C)-(278)427) in other reactions they have given hydrazones, or have been converted into pyrazoles and fused heterocyclic rings (77JAP(K)7785194), e.g. (72) -> (73). 

Table 21 Monosubstituted Heterocycles Ring Stretching Bands in the 1600-1300 cm Region

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