Ring Carbon

Initial attempts to extend this type of reaction to less activated systems were unpromising, until the requirement for two equivalents of LDA was realized (92T939) it was proposed that a dianion, e.g., 174, was involved. Although details of the reaction pathway remain unclear, this type of reac- 

An analogous pathway could be involved in the formation of 4-formyl-2-azacycl[3.2.2]azine (180) in 14% yield by treatment of 5-methylimidazo[l,5-fl]pyridine (179) with butyllithium and DMF, but the route suggested (75JOC1210), via the dialdehyde, (181) is also possible. 

Reaction with Thionyl Chloride and Sulfuryl Chloride 

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These genera] trends direct the organization of Chapters VI and VII syntheses from the already formed thiazole ring, physicochemical studies, ambident reactivity ring carbon reactivity, main derivatives, and aminothiazole applications. 

The reasonable stable products are characterized by an ir-absorption near 1615 cm". The 4-protons resonate near 6.2 ppm in the H NMR spectrum (23). NMR spectra exhibit a carbonyl atom signal near 173 ppm, whereas C-4 resonates near 8 108 these positions are characteristic of other mesoionic ring carbon atoms (24). In the mass spectra, decomposition with loss of CO, rupture of the 1,5 and 2.3 bonds with elimination of R NC2R 0 and cleavage of the 1,2 and 3,4 bonds with elimination of C2R 0S is observed (11)... 

The interaction between a substituent and the ring carbon to which it is bonded could be related to some electronic characteristics of the unsubstituted ring and especially to the net charge of its various sites. In that respect the rr-net charges diagram discussed in Section 1.5 indicates that the electron-withdrawing power of the ring-carbon atoms will decrease in the order, 2>4>5. 

In the Z stereoisomer the two lower priority substituents—the methyl group and the hydrogen—are on the same side of the double bond In the E stereoisomer these substituents are on opposite sides of the double bond The ring carbons are the higher ranking substituents at each end of the double bond y... 

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... 

How do the charges on the ring carbons of toluene and (tri fluoromethyl)benzene relate to the regioselectivity of nitration" ... 

A methyl group is an electron releasing substituent and activates all of the ring carbons of toluene toward electrophilic attack The ortho and para positions are activated more than the meta positions The relative rates of attack at the various positions m toluene compared with a single position m benzene are as follows (for nitration at 25°C)... 

Of the sp hybridized carbons C 1 is the most shielded because it is bonded to only one other carbon The least shielded carbon is the ring carbon to which the side chain is attached It is the only sp hybridized carbon connected to three others... 

The ring carbons of an epoxide are somewhat more shielded than the carbons of a C—O—C unit of larger rings or dialkyl ethers... 

The aromaticity of the nng is retained when chlorine bonds to the benzyhc carbon aro maticity is lost when chlorine bonds to one of the ring carbons... 

Substituents on both sides of the double bond are considered separately. Additional vinyl carbons are treated as if they were alkyl carbons. The method is applicable to alicyclic alkenes in small rings carbons are counted twice, i.e., from both sides of the double bond where applicable. The constant in the equation is the chemical shift for ethylene. The effect of other substituent groups is tabulated below. 

Ring-atomic centers can undergo attack by electrophiles, easily at the ring nitrogen and less easily at ring carbons. Nucleophilic attack is also possible at ring carbons or hydrogens. 

N. J. Fechter and P. S. Petmnich, Development of Seal Ring Carbon-Graphite Materials., NASA Contract Reports CR-72799, Jan. 1971 CR-72986, Aug. 1971 CR-120955, Aug. 1972 and CR-121092, Union Carbide Corp., Parma, Ohio, Jan. 1973. 

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