Of positional isomers

The number of naphthalene derivatives is very large, since the number of positional isomers is large 2 for monosubstitution, 10 for disubstitution—same substituent, 14 for disubstitition—different substituents, 14 for trisubstitution—same substituent, 42 for trisubstitution—two different substituents, 84 for trisubstitution—three different substituents, and so on with multiplying complexity. 

The reaction of arylnitrile oxides with 1,1-diphenylallenes gave a mixture of 4-methylene-2-isoxazolines (Scheme 106) with major attack at the C(2)—C(3) double bond (74JCS(P2)l30l, 76CSC67, 76CSC71, 72JCS(P2)1914) and not a mixture of the 4- and 5-methylene compounds. 1-Phenoxyallene and benzonitrile oxide produced a mixture of positional isomers and a spiro compound (Scheme 107) (79JOC2796). 

The following ortho esters have been prepared to protect the diols of nucleosides. They are readily hydrolyzed with mild acjd to afford monoester derivatives, generally as a mixture of positional isomers. 

Azidofurazans and -furoxans undergo dipolar cycloaddition reactions with unsaturated compounds, in some cases regiospecifically. Thus, reaction of 3-amino-4-azidofurazan with l-morpholinyl-2-nitroethene (toluene, reflux, 70 hours) gives 4-nitro-l,2,3-triazole 204 in 87% yield (99MI1, 000KGS406). Cycloaddition of the same azide to alkynes was accomplished by formation of a mixture of position isomers 205 and 206. Regiospecific addition was observed only in singular cases... 

Hardy, M. R. and Townsend, R. R., Separation of positional isomers of oligosaccharides and glycopeptides by high-performance anion-exchange chromatography with pulsed amperometric detection, Proc. Natl. Acad. Sci. U.S.A., 85, 3289, 1988. 

Fujiwara, S. and Honda, S., Effect of addition of organic solvent on the separation of positional isomers in high-voltage capillary zone electrophoresis, Anal. Chem., 59, 487, 1987. 

Hamai S. and Sakurai H., Capilary electrophoretic separation of positional isomers of hydroxynaphthalenecarboxylic acids through the formation of inclusion complexes with P-cyclodextrin, Anal. Chim. Acta, 402, 53, 1999. 

OH elimination from ortho substituted aldoximes 179 (X = CH2, NH, O) may be at least partially the result of a hydrogen migration/cyclization/elimination process, whereby the heterocycles 182 are formed72 (46). A metastable peak shape analysis, the investigation of 2H-labelled derivatives and the study of positional isomers indicate that in addition to 182 the protonated isocyanide 183 is formed via a mechanism which is not fully understood. However, it is known that the generation of 183 occurs without any detectable interaction with the XH ortho substituent. 

On a capillary GC analysis, the separation of positional isomers of epoxy compounds is generally well accomplished by a high polar column, such as DB-23, rather than by a low polar column, such as DB-1. For the positional isomers, a different elution order depending on the kinds of column has not been reported. In the case of two mono epoxides derived from Z6,Z9-dienes, 6,7-epoxides elute slightly faster than 9,10-epoxides [72,170],but the separation is insufficient even on the high polar column. Three monoepoxides derived from Z3,Z6,Z9-trienes elute in the order of 6,7-, 3,4-, and 9,10-epoxides [9]. The former two isomers are sufficiently separated on the high polar column, while the elution of the latter two isomers overlaps [71]. For each positional isomer of diepoxides derived from the Z3,Z6,Z9-trienes, two diastereomeric... 

Ferreres F, Llorach R and Gil-Izquierdo A. 2004. Characterization of the interglycosidic linkage in di-, tri-, tetra- and pentaglycosylated flavonoids and differentiation of positional isomers by liquid chromatogra-phy/electrospray ionization tandem mass spectrometry. J Mass Spectrom 39(3) 312—321. 

This stearolic acid has been thoroughly characterized 3 6 by the freezing-point curve, ultraviolet and infrared spectra, ozonization, and hydrogenation. It has been shown to be free both of positional isomers and of olefinic acids such as oleic and elaidic acids. Its properties include m.p. 46-46.5°, iodine number (Wijs titration, 30 minutes) 89.5, d 5 1.4510, d 5 1.4484, neutral equivalent 279.2-279.6 (theory 280.4), hydrogen uptake 95-100% of theory for a triple bond. The last trace of color is difficult to remove by recrystallization from petroleum ether. It can be removed, however, by crystallization from a 20-30% solution in acetone at —5 to —8°, or from an 8-10% solution at —20°, or by distillation (b.p. 189-190°/2mm.). 

Furoxan derivatives can consequently exist as a pair of position isomers when the substituents at the ring are different. Conventionally it is numbered assigning... 

Wiench et al. investigated chemical shifts of a set of positional isomers of azaindolizines <1994MRG373>. In Table 3, 13C and 1SN NMR chemical shifts of two related ring systems, the unsubstituted [l,2,4]triazolo[l,5- ]-pyrimidine A and [l,2,4]triazolo[3,2- ]pyrimidine B, are compared. 

Korner s method org chem A method for determining the absolute position of substituents for positional isomers in benzene by the experimental production of positional isomers from a given disubstituted benzene. kor-norz, meth-3d ... 

Scheme 15 Synthesis of positional isomers of pyrazolopyridine carboxylic acid derivatives...

Scheme 20 Formation of position isomers in MCRs of aminotriazole...

Scheme 45 Formation of position isomers in Groebke-type reactions...

The use of sulfuryl chloride for free radical chlorination of aliphatic carboxylic acids gives mixtures of positional isomers.7 However, with the cyclobutane ring, the attack is much more selective. The present method provides a procedure for free radical halogenation of a cyclobutane ring. 

The crystalline monoadduct 8 has been reported to undergo a regiospecific thermal disproportionation into a solid 1 1 mixture of Cgo and the trans-l bisadduct isomer 9a (Scheme 6) [36]. However,bisadducts 9 obtained under the HSVM conditions were a mixture of positional isomers [35]. 

U. Sidelmann, S.H. Hansen, C. Gavaghan, A.W. Nicholls, H.A.J. Carless, J.C. Lindon, I.D. Wilson, J.K. Nicholson, Development of a simple liquid chromatographic method for the separation of mixtures of positional isomers and anom-ers of synthetic 2-, 3- and 4-fluorobenzoic acid glucuronides formed via acyl migration reactions, J. Chromatogr. B Biomed. Sci. Appl. 685 (1996) 113-122. 

The comparison of UV spectra of isomers is of particular interest (Table 9) it is apparent in each pair of positional isomers, that increasing the number of conjugated double bonds shifts the characteristic wave length towards higher values. Moreover, the shift is the more pronounced, the higher the percentual increase in the number of conjugated double bonds is. 

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