Isomerism substitutional

In the reaction of 4-substituted 2-aminoselenazoles with ethyl propiolate and dimethylacetylene dicarboxylate. the major products obtained from such a condensation are substituted 7H-selenazolo[3,2-a]pyrimidin-7-ones (5) and not the alternative isomeric substituted 5H-selenazoles[3,2-a]pyrimidin-5-ones (6). Distinction between the alternative structures was based on infrared, ultraviolet, and NMR data (Scheme... 

Two isomeric arynes give the three isomeric substitution products formed from m chloro toluene... 

As an example we calculate the number of different isomeric substitutes of cyclopropane of the form... 

In the presence of an oxidizing species (oxygen, iodine, tetracyanoethylene and others) DHP is dehydrogenated into phenanthrene. This oxidation can also be thermal or photochemical. In general, meta substituted stilbenes give rise to two isomeric substituted phenanthrenes ortho-substituted stilbenes can lose the substituent on cyclization. 

The sulfur tetrafluoride fluorination of most nonhalogenated quinones and hydroxyquinones is erratic in behavior and generally occurs with isomerization, substitution of a hydrogen atom by fluorine, and addition of fluorine to the carbon atom / to the carbonyl group. Thus, the fluorination of benzo-l,4-quinone results in aromatization to give 1,2,4-trifluorobenzene (8) as the sole product.41... 

Evidence for the configurations, i.e. the cis/trans relationship of a substituent with respect to the bridgehead hydrogen atoms, has also been presented. An a priori estimation of the relative stabilities of isomeric substituted indolizidines, assuming a trans junction between the rings, led to the conclusion that equatorial substituents in the six-membered ring and pseudo equatorial substituents in the five-membered ring are thermodynamically favoured. 

Figure 11.2.2 Miscibility of isomeric -substituted 2-amino-ethanols with water [4].

Study of isomer distribution in substitution of benzene rings already carrying one substituent presents some potential pitfalls. Inspection of product ratios for ortho, meta, and para substitution, as in investigation of electrophilic substitution (Section 7.4, p. 392), might be expected to give misleading results because of the side reactions that occur in radical substitution. The isomeric substituted cyclo-hexadienyl radicals first formed by radical attack partition between the simple substitution route and other pathways (Equation 9.102). In order for the... 

Mixed metal clusters (clusters containing two different metals) have considerable potential for mechanistic studies. Three separate studies on iron mthenium clusters show the possibilities. Reactions of FeRu2(CO)i2 and Fe2Ru(CO)i2 in comparison to Fe3(CO)i2 and Ru3(CO)i2 show a very interesting activation of the iron center towards CO dissociation by ruthenium centers in the mixed metal-cluster system. Such an activation of the iron center by ruthenium has also been demonstrated for (/r-H)FeRu2(/(r-COMe)(CO)io. The presence of different metal centers for H2FeRu3(CO)i2 allowed unusually detailed interpretation of the isomerization, substitution, and CO exchange reactions. ... 

Dichloro(l, 3-propanediyl)platinum and its bis(pyridine) derivative have been studied by a number of authors. Dichloro(l,3-propanediyl)platinum, and the corresponding substituted 1,3-propanediyl platinum compounds release the parent cyclopropane on treatment with potassium cyanide, potassium iodide, a tertiary phosphine, carbon monoxide, and other ligands.2,6 Reduction by means of hydrogen or lithium aluminum hydride yields chiefly isomeric substituted propanes. Dichlorobis(pyridine)(l,3-propanediyl)platinum in refluxing benzene yields a pyridinium ylid complex, - (CH3CH2CHNC5Hs)-PtpyCla. 

The TTyir singlet states of the cyclopropenes (101) are reactive and lead to re2irrangement products by way of a carbene (102) mechanism as outlined above. Typical examples of the reaction are shown in the Scheme 8, where it can be seen that the rearrangement affords the isomeric substituted furans (103) and (104) from (101, X = 0) and pyrroles (105) and (106) from (101, X =NMe). This latter reaction also yields the diene-substituted pyrrole (107), which is good evidence for the proposed carbene mechanisms. The thiophene derivative (101, X = S) yields a single product (108) on photoexcitation. 

Since similar propargylic spectra are obtained, starting from isomeric substituted acetylenes and allenes, we conclude that this surface species does act as a catalytic intermediate. This clarifies the mechanism isomerization apparently occurs via a... 

A study of the isomeric substitution products of benzene reveals some striking facts which furnish the strongest support for the accepted structural formula. 

Isomerism.— An examination of the formula for anthracene will show that the number of isomeric substitution products may be greater in number than in the case of naphthalene. The facts in regard to the mono- and di-substitution products are that there are three mono-substitution products and fifteen di-substitution products with like substituents. Numbering the positions in the anthracene formula we have ... 

Quadricyclane may be prepared by direct irradiation of bi-cyclo[2.2.l]hepta-2,5-diene and 2,3-diazatetracyclo[4.3.0.0. -0 ]non-2-ene or by photosensitized isomerization of bicyclo-[2.2.1]hepta-2,5-diene. Several substituted quadricyclanes have been prepared by direct irradiation and by photosensitization. The procedure described above can be used to isomerize substituted bicycloheptadienes to the corresponding quadricyclanes when traces of sensitizers can be conveniently removed or their presence does not interfere with further use of the quadricyclane. 

What does this suggest about the arrangement of atoms in methane It suggests that every hydrogen atom in methane is equivalent to every other hydrogen atom, so that replacement of any one of them gives rise to the same product. If the hydrogen atoms of methane were not equivalent, then replacement of one would yield a different compound than replacement of another, and isomeric substitution products would be obtained. 

Kekul, A. (1829-1896). Laid foundations of aromatic chemistry conceived of four-valent carbon and structure of benzene ring predicted isomeric substitutions (ortho-, meta-, para-). 

The success of cycloisomerization reactions of this type is critically dependent on factors that influence the conformational mobility of the side chain bearing the alkene moiety. Additionally, functional groups which are able to serve as ligands at palladium may also be of importance. As an example, neither the (E)- nor the (Z)-crotonate derivative ( -IS or (Z)-13 gives rise to the formation of bicyclic products on treatment with bis(dibenzylideneacetone)palladium/tri-isopropyl phosphite. Instead, the corresponding isomeric substituted butadienes, methyl (2E or 2Z,6 )-7,8-dimethylnona-2,6,8-trienoate (14) and methyl (2E or 2Z)-8-methyl-7-methyl-enenona-2,8-dienoate (15), are formed. 

As in the corresponding thermal solvolysis (see Scheme 28) two unrearranged enol ethers, E- and Z-38, are formed but, in marked contrast, also a rearranged enol ether 80 (and its hydrolysis product 81). The ratios of formation of unrearranged/ rearranged substitution product (38/80 + 81) of ElZ isomeric substitution product (E-3SIZ-3S), and of substitution/elimination (38 + 80 + 81/39) depend on the solvent used (Table 15). 

It has been known since the early days that behavior of the aromatic polyamides (aramids or PARA) critically depends on the type of isomeric substitutions — para resulted in crystalline, while meta in amorphous resins [Kwolek et al, 1962]. 

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