Isomery bonding

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,... 

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,... 

Geometric isomers or cis-trans isomerism can exist in compounds th6i contain a double bond or a ring structure. In order for this type of isomerism— to exist the groups coming off the same end of the double bond must be different. For example bromoethenc does not have cis-trans isomeri nT ... 

Bond isomery describes the isomers with different coordination mode of ligands on different donor centers [3,4]. 

The nitrite anion takes part in numerous complexes for which the bonding isomery is assumed, leading to the eight types of isomers 90-97 [3,13,112,116,117,123-126] ... 

Bond isomery [described by Scheme (2.1)] is frequently observed in complexes with the structures 107 and 108 [48,117,162-164] ... 

However, all the ICC obtained by using chemical (mainly, immediate interaction of ligands and metal salts) or electrochemical methods have the structures 903 or 904. Enormous amounts of literature related to these syntheses are mainly found in monographs [55,56] and reviews [11,229,230]. The bonding isomery, which caused the possibility of formation of structures 904 or 905, was also discussed [11,231]. 

An X-ray structure analysis of red rodlets isolated from an 1,2-dimethoxyethane/npentane solution at -5 shows the compound to crystallize as a Z-isomerie neutral complex (Fig. 10). P-C and C-N bond lengths of 176.9 and 132.3 pm respectively are in good agreement with the formation of an electronically stabilized mesomeric heteroallyl anion. Lithium primarily bound to nitrogen and two oxygen atoms of the 1,2-dimethoxyethane ligand increases its coordination number from 3 to 4 or probably 5 by interactions with the i/7JO-carbon of the phenyl substituent and phosphorus. 

Reductive dehalogenation with tin hydrides can be carried out without interference of a number of functional groups. However, a C-C double bond in a 1,5 relationship to the intermediate cyelopropyl radical can function as a trap and result in formation of bicyclo[3.1.0]hexane derivatives. Thus, treatment of l,l-dibromo-2-(but-3-enyl)cyclopropane with tributyltin hydride afforded a 15 85 mixture of l-bromo-2-(but-3-enyl)cyclopropane (13) and 1-bromo-2-methyl-bicyclo[3.1.0]hexane (12). Under similar conditions l-bromo-2,8,8-trimethyltricyclo-[3.2.1.0 ]octan-3-one (15) was obtained in 6% yield from an isomeric mixture of 7,7-dibromo-4-isopropenyl-l-methylbicyclo[4.1.0]hept-2-one the main product, isolated in 86% yield, was an isomerie mixture of 7-bromo-4-isopropenyl-l-methylbicyclo[4.1.0]hept-2-one (14). ... 

S. J. Miller (Chevron) published results from early work that highlighted the selectivity of the platinum form of SAPO-11 catalyst compared to a number of others. These others were amorphous silica-alumina, from which one would expect little or no selectivity, ZSM-5, HY, and Na-Beta zeolites. All the catalysts carried 1 wt. % platinum and the feed employed was n-octane. He found that at 30% conversion, only SAPO-11, the amorphous silica-alumina, and the HY catalysts exhibited better than 94% selectivity for feed isomerization to isooctanes. ZSM-5 and Na-Beta catalysts behaved poorly in this regard. Selectivity for dimethylhexanes was low. SAPO-11 also produced equal quantities of 2- and 3-methyl heptanes, whereas the other catalysts favored 3-methyl heptane, with a ratio close to that favored by thermodynamics. SAPO-11 also produced one of the lowest levels of doubly-branched hexanes (Table 10.1646) and the predominant ones formed were those separated by more than one carbon—only minor amounts of the less thermally stable (bond breaking here can produce tertiary carbonium ions) geminal-dimethyl (2,2 and 3,3-) ones were formed. Noble metal presence was a key to success since replacement of the hydrogenation metal platinum by pallodium did not alter the isomeri-zation selectivity much, but replacement by nickel led to very poor isomerization. 

Dissociative processes were also implicated in HCl cleavage reactions of ci5-[PtMeR(PEt3)2] (R = methyl, phenyl, or mesityl) and their subsequent isomeri-zations. The cleavage mechanism is believed to involve a fast preequilibrium between substrate and chloride, combined with a parallel protonation of both platinum species, where the proton attacks the Pt—Me bond (Scheme 3). The spontaneous isomerization of the solvated intermediates ci5-[PtR(S)(PEt3)2] was followed either by P NMR or UV/visible spectroscopy. Dissociative loss of the solvent molecule, S, was implicated because of the relative insensitivity of the reaction rate to the steric bulk of R, and because of the positive values of AS. ... 

Dicyclopentadiene, which has no possibility of double bond isomeri-2ation, reacts smoothly to dialdehydes or, at higher temperature, to diols [254]. An isomer mixture is obtained in a ratio of 1 3. 

Draw bond-line formulas and give lUPAC substitutive names for all of the isomerie alcohols with the formulas (a) C4H10O and (b) C5H12O. 

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