Isomerie

In Ubergangsmetallkomplexen sind verschiedene Arten von Isomerie anzutreffen. 

Geometrische Isomerie Quadratisch planare Komplexe, MA2B2 unterliegen der cisItransAsomtnt. Zum Beispiel Pt(NH3)2Cl2 

Optische Isomerie Ein Komplex ist chiral, wenn er keine Drehspiegelachse S enthalt. Zu einem chiralen Komplex gibt es immer ein Spiegelbild, Enantiomer genannt, z.B. 

Eine Mischung optisch aktiver, kationischer Komplexe uberfiihrt man durch Reaktion mit optisch aktiven Anionen in Diastereomere, die sich aufgrund ihrer verschiedenen physikalischen Eigenschaf-ten (Schmelzpunkt, Loslichkeit, etc.) voneinander trennen lassen. 

Ein weiteres Beispiel ist NiCl2py2, das im festen Zustand aus einer polymeren Kette mit ok-taedrisch koordiniertem Nickel besteht. 

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Without assuming something specific about the reaction rate, it is not possible to go further and actually determine the micropore fluxes. We shall therefore consider the particular case of a first order reversible isomeri-... 

W hich leads to an isomeri/ation enthalpy of —1.7 kcal mol. ("Heat of fonnation should he taken to mean enthalpy of formation in this conte.st.) Entropy effects being... 

Xylene Isomeri tion. The objective of C-8-aromatics processing is the conversion of the usual four-component feedstream (ethylbenzene and the three xylenes) into an isomerically pure xylene. Although the bulk of current demand is for xylene isomer for polyester fiber manufacture, significant markets for the other isomers exist. The primary problem is separation of the 8—40% ethylbenzene that is present in the usual feedstocks, a task that is compHcated by the closeness of the boiling points of ethylbenzene and -xylene. In addition, the equiUbrium concentrations of the xylenes present in the isomer separation train raffinate have to be reestabUshed to maximize the yield of the desired isomer. 

However, an elegant O nmr study using specifically labelled [CoINHslsl ONO)] " and (Co(NH3)5(ON 0)] established that spontaneous intramolecular O-to-O exchange in the nitrite ligand occurs at a rate comparable to that of the spontaneous O-to-N isomeri /ation/ ° ... 

Acetylene interaets with hydrazine in absolute ethanol to give a mixture of isomerie hydrazones in a 3 2 ratio (by NMR speetra) (68LA117) (Seheme 89). 

In eontrast, the isomerie 5-alkynylpyrazole-4-diazonium ehlorides eyelized only after heating tol00-105°C for 2 h, giving good yields of the l,3-dimethyl-7-ehloro-l//-pyrazolo[4,3-c]pyridazines 87 [98HEC519 99JCS(P1)3721] (Seheme 137). 

Likewise, the ynaminoketones with phenylhydrazine give a similar mixture of isomerie l-phenyl-3-dialkylammo-5-methylpyrazoles (369) and l-phenyl-5-dialkylamino-3-methylpyrazoles (370) in the same 3 4 ratio (87ZOR1635). 

Three elasses of triazoloquinolines may exist based on the fusion of the triazole ring on faee a, ij or j. This eould lead to eight isomerie eompounds as shown in Fig. 9. 

The earboxylie aeid derivative of an isomerie fused thienopyrimidine exhibits mediator release inhibiting activity. The apparently complex thiophene 126 can be obtained in a single step by... 

Several approaches based on nitro-aldol for the synthesis of amino sugars have been reported Alumina-catalyzed reaction of methyl 3- nitropropanoate with O-benzyl-o-lactaldehyde gives the o-ribo-nitro-aldol fanti, and isomeri in 63% yield, which is converted into L-dannosamine fsee Secdon 3 3 Jager and coworkers have reported a short synthesis of L-acosamine based on the stereoselective nitro-aldol reaction of 2-O-benzyl-L-lactaldehyde with 3-nitropropanal dimethyl acetal as shovm in Scheme 3 10 The stereoselecdve nitro-aldol reacdon is carried ont by the silyl nitronate approach as discussed in Secdon 3 3... 

Isomerie,/. isomerism, -fall. m. case of isomerism. -mdglichkeit, /. possibility of isomerism. 

Kem-isomer, n. nuclear isomer, ring isomer, -isomerie, /. nucleus (or nuclear) isomerism, -kbrper, m., -korperchen, n. nucleolus, -la-dung,/. nuclear charge main charge, -la-dungszahl, /. nuclear-charge number, atomic number, -leder, n. butt or bend leather. 

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. 

Orts-funktion, /. position ftmction. -isomerie, /. place isomerism, position isomerism, Ortsteln, m, Min.) bog iron ore hardpan, ortsverinderlich, a. movable, portable, Orts-verinderung,/. change of position, -wech-sel, m. change of position or location, -zahl, /. position number, index number. 

Raum-isomerie, /. spatial isomerism, stereoisomerism. -kurve, /. solid curve, -lehre, /. geometry. 

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. 

The rapid formation of the (Z)-diazoate is followed by the slower (Z/J )-isomeri-zation of the diazoate (see Scheme 5-14, reaction 5). Some representative examples are given in Table 5-2. Both reactions are first-order with regard to the diazonium ion, and the first reaction is also first-order in [OH-], i.e., second-order overall. So as to make the rate constants k and k5 directly comparable, we calculated half-lives for reactions with [ArNj ]0 = 0.01 m carried out at pH = 9.00 and 25 °C. The isomerization rate of the unsubstituted benzenediazonium ion cannot be measured at room temperature due to the predominance of decomposition (homolytic dediazoniations) even at low temperature. Nevertheless, it can be concluded that the half-lives for (Z/ )-isomerizations are at least five powers of ten greater than those for the formation of the (Z)-diazohydroxide (reaction 1) for unsubstituted and most substituted benzenediazonium ions (see bottom row of Table 5-2). Only for diazonium ions with strong -M type substituents (e.g., N02, CN) in the 2- or 4-position is the ratio r1/2 (5)/t1/2 (1) in the range 6 x 104 to 250 x 104 (Table 5-2). 

The problems of moving the double bond and getting the rj ghL stereochemistry at the third chiral centre in ( 41 ) turned out to bo trivial isomeri sat i on wi tii HC1 achieved both. The final reduct.ion was done in two stages with special reagents,... 

Blua, M. J., Hanscom, Z. and Collier, B. D. 1988. Glucocapparin variabdity among four populations of Isomeris arborea Nutt. J. Chem. Ecol. 14 623-633. 

The different coordination behaviour of F- and 0-ligands in the [P03F] ion becomes evident in the interesting structural isomery of (NH4)2P03F H2O (26) and (NH4)2S03 H2O (28) also, the stmctural parameters of which are very much alike -the part of the F-atom in the fluorophosphate being played by the lone electron pair in the sulfite ion. 

Sehechter, M. MDMA as a discriminative stimulus Isomerie eomparisons. Pharmacol Biochem Behav 27 41-44, 1987. 

Als Bestatigung fur die Struktur ist die saurekatalytische Isomeri-sierung der cis-Verbindung CCCXXVIII zur racemischen trans-Ver-bindung zu werten, die offenbar nach folgendem Schema verlauft ... 

Abb. 19. Das Verhalten der cr-Orbitale [Pg.221]

Abb. 20. Den EH-Berechnungen zugrunde gelegte Modell-Strukturen fiir die bond/ stretch-Isomerie 4, mit einem Freiheitsgrad (a) 5, mit drei Freiheitsgraden (a,... 

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