Chain isomerism

Complications arising from other types of chain isomerism, such as those mentioned in Sec. 1.6. 

Some 4,5-disubstituted pyridazines exhibit ring-chain isomerism involving heterospiro compounds. For example, 5-(o-aminophenylcarbamoyl)pyridazine-4-carboxylic acid exists in a zwitterionic form in the solid state, but in a solution of DMSO it is almost exclusively 3, 4 -dihydro-3 -oxospiro[pyridazine-5(2//),2 (l //)-quinoxaline]-4-carboxylic acid (134). The equilibrium is strongly influenced by the nature of the solvent, the substituents on the pyridazine ring and the nucleophilicity of the group attached to the phenyl ring (Scheme 48) <80JCS(P2)1339). 

The ring-chain isomerism was studied in a series of 4-hydroxy-3,4-dihydro-1,2,4-triazines 87, which are models for cr -adducts at the 3 position of the... 

Ketten-glied. n. link (or member) of a chain, -isomerie, /. chain isomerism, -kokken, m.pl. streptococci, -linie,/. catenary (curve), -moldktil, n. chain molecule, linear molecule, -polymer, n. chain polymer, linear polymer, -rad, n. sprocket wheel, -reaktion, /. chain reaction, -trieb, m. chain drive. 

Selten-gummi, n. side wall (of a rubber tire), -isomerie, /. chain isomerism, -kante, /. lateral edge, -kette, /. side chain, -ketten-isomerie, /. side-chain isomerism, -kraft, /. component force, component, -lage,/. lateral position, -l ge, /. length of a side, lateral length, -riss, m. side elevation. -lohr, n., -rohre,/. side tube, branch tube, branch pipe, seitens, adv. on behalf (of), on the part (of), seltenstandlg, a. lateral. 

There are two important rhodium-catalyzed transformations that are broadly used in domino processes as the primary step. The first route is the formation of keto carbenoids by treatment of diazo keto compounds with Rh11 salts. This is then followed by the generation of a 1,3-dipole by an intramolecular cyclization of the keto carbenoid onto an oxygen atom of a neighboring keto group and an inter- or intramolecular 1,3-dipolar cycloaddition. A noteworthy point here is that the insertion can also take place onto carbonyl groups of aldehydes, esters, and amides. Moreover, cycloadditions of Rh-carbenes and ring chain isomerizations will also be discussed in this section. 

The alkanes make up a homologous series of hydrocarbons with the general formula C H2 +2 in is the number of carbon atoms). Alkanes exhibit a type of structural isomerism called chain isomerism, where the arrangement of the carbon atoms in the molecules is different. 

Cycloaddition of pyridine Ar-oxides (see Section 11.13.2) led to careful examination of thermodynamic aspects, though no experimental measurement was provided. Thermodynamic profile for the ring-chain isomerization of [l,2,3]triazolo[l,5- ]pyridines via a ring-opening pathway (Equation 2) was calculated. Based on this computational study, a multistep mechanism was proposed <20050BC3905>. 

M11 R. E. Valters, Ring-Chain Isomerism in Organic Chemistry (in... 

The imidoyl azide-tetrazole ring-chain isomerism of tetrazoles develops into a wide-ranging example of the Dimroth rearrangement in the thermal behavior of substituted 5-aminotetrazoles <84JHC627>. An example with 5-hydrazinotetrazoles is shown in Scheme 10 <88BSB543>. The reaction... 

Horton,however, correctly observed that the product obtained by Friedmann could have the structure of thieno[3,2-6]thiophene (2) type rather than that of 1, since 2,5-dimethylthieno[3,2-6] iophene (18) can be formed by ring closure through sulfur bridging without carbon chain isomerization [Eq. (3)]. 

Side-Chain Isomerization. Arylalkanes undergo acid-catalyzed isomerization in the side chain in a way similar to the skeletal rearrangement of alkanes.70-72 There are, however, notable differences. Propylbenzene, for instance, yields only a small amount (a few percentages) of isopropylbenzene 73 Similarly, sec-butyl- and iso-butylbenzene are interconverted at 100°C with wet A1C13, but only a negligible amount of tert-butylbenzene is formed.74 In the transformation of labeled propylbenzene the recovered starting material was shown to have equal amounts of labeling in the a and p positions of the side chain, but none in the y position 73... 

The Tautomerism of Heterocycles J. Elguero etal., Adv. Heterocycl. Chetn., Suppl. 1,1976. Ring-Chain Isomeric Transformations of Hydroxy-, Amino-, and Mercapto-Derivatives of Carbonyl Compounds and Their Heteroanalogues R. Valters, Russ. Chem. Rev. Engl. Transl.), 1974, 43, 665-678. 

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