Isomer-selectivity

Mononitration of a mixture of J- and 4 chlorobenzotnfluondes followed by nucleophilic substitution by hydroxide, ammonia, or a primary or secondary amine in dimethylformamide, leads to 5 chloro 2 nitrobenzotrifluoride The 4-chloro-3-nitro isomer selectively reacts and can be removed as a water-soluble phenoxide [19] (equation 16)... 

The preparation of cyclopentadienes with up to four trimethylsilyl groups can be performed easily on a large scale starting with monomeric cyclopentadiene by repeated metalation with n-butyllithium and treating the resulting anion with chlorotrimethylsilane [84], Any complication caused by formation of regioisomers does not occur, since all trimethylsilyl-substituted cyclopentadienes are fluxional by virtue of proto- and silatropic shifts [85], Upon deprotonation with n-butyllithium the thermodynamically most favorable anion is formed selectively (Eqs. 20, 21). Thus, metalation of bis(trimethylsilyl)cyclopentadiene 74, which exists preferentially as the 5,5-isomer, selectively affords the 1,3-substituted anion 75. Similarly, tris(trimethylsilyl)cyclopentadiene 76, which is found to be mainly as the 2,5,5-isomer, affords the 1,2,4-substituted anion 77. 

A series of 2-(4-chlorophenoxy)-3-oxoalkanoate were reduced by baker s yeast, and Kluyveromyces marxianus. Yeast reduction of ethyl 2-(4-chlorophenoxy)-3-oxo-3-phenylpropanoate (R=Ph) afforded enantiomerically pure ethyl 2R, 3S)-2-(4-chlorophenoxy)-3-hydroxy-3-phenylpropanoate out of the four possible stereoisomers in >99% de [29h]. Although baker s yeast reduction of butanoate (R = CFl3) was not selective (92% de), the use of K. marxianus afforded (2R, 3S)-isomer selectively [29i]. The products are intermediates for potential peroxisome prolifera-tor-activated receptor isoform a-agonists (Figure 8.39a). 

During, A. et al.. Carotenoid uptake and secretion by Caco-2 cells 3-carotene isomer selectivity and carotenoid interactions, J. Lipid. Res., 43, 1086, 2002. 

The affinity of platinum(II) for N-donor ligands is well established. There are numerous examples in the literature of mono-, di-, and trinuclear platinum(II)-ammine and alkylamine complexes, most of which are structural analogues of the anticancer agent, mplatin (cis- PtCl2(NH3)2]), and the corresponding trans isomer. Selected novel complexes and synthetic methods are presented below. 

The P-C isomer selectivity seems to be tissue-specific a preferential uptake of the all-trans isomer was shown in hepatic stellate HSC-T6 cells and in cell-free system from rat liver microsomes, but not in endothelial EAHY cells or U937 monocyte-macrophages (During et al., 2002). When Caco-2 cells were incubated with only 9-cis P-C, all -trans P-C did not increase in cells or in the basolateral medium, indicating that there is no cis-trans isomerization occurring in intestinal cells. Thus, the isomerization of 9-cis P-C observed in vivo (You et al., 1996) could take place in the... 

Q5. Check out the proton spectrum first Extract as much information as possible before considering any of the other spectra. Given that the proton spectrum serves to eliminate most of the potential isomers, select the spectrum that yields the information required most directly and unambiguously. 

Method B In contrast, reprotonation of the tert-butyldimethylsilyl-protected nitronate anions gives awh-isomers selectively (41 9-19 1). 

Selectivity refers to the fraction of raw material alkene that is converted to product aldehyde, but since hydroformylation typically gives both a linear and branched isomer, selectivity also refers to the relative amounts of each. The linear branched (l b) ratio is highly catalyst dependant. One must simultaneously consider whether the proposed catalyst will give the desired l b selectivity and also whether the proposed catalyst is feasible for use with the catalyst/product separation technologies. For example, water extraction of a polar product, such as in the hydroformylation of allyl alcohol to give 4-hydroxybutanal, would not work well with a sodium salt of a sulfonated phosphine since both are water soluble. 

Olefin feed h3/co Linear isomer (%) Selectivity to aldehyde (%)... 

Alkylation of purine derivative 72 yields an N-7/N-9 regioisomer (73/ 74) mixture which can be purified using aluminium oxide/H+ to provide the N-9 isomer selectively as a parallel or chemoselective high-throughput purification <00TL3573>. 

Liu W, Gan JJ, Lee S, Werner I (2004) Isomer selectivity in aquatic toxicity and biodegradation of cypermethrin. J Agric Food Chem 52 6233-6238... 

Isomer-selective reactions do not occur in the various environmental processes in estuaries, and therefore fate analysis of NP and APEO can be expressed in terms of sum of all the alkyl isomers [25]. 

Number of compounds designed 5614 Number of compounds selected 59 Number of isomers designed 133 Number of isomer selected 111 T otal time used to design 1.97 ... 

Cathodic reduction of bicyclic gem-dibromocyclopropane in the presence of chlorotrimethylsilane provides the exo-silylated isomer selectively. With a sacrificial Mg anode the current efficiency can be increased by sonication as the anode acts additionally as a chemical reducing agent [358]. The 2e reduction of (5 )-(+)-l-bromo-l-carboxy-2,2-diphenylcyclopropane showed that the stereoselectivity at a Hg cathode was strongly determined by the supporting electrolyte cation. With NH4+, a preferential retention of configuration was observed, which increased with a more negative reduction potential. By contrast, a R4N+ cation gives rise to a major inversion, which increases with the bulkiness... 

I isom = selectivity for 2-octene. lib = linear to branched ratio of... 

To synthesize the sixth dithienothiophene isomer, selective bromina-tion of 3-bromo-2,3 -dithienyl (187) gave an almost quantitative yield of 2,3 -dibromo-3,2 -dithienyl (188). Dithienyl 188, with butyllitMum (1 equiv.) and sulfur, was converted into the unstable thiol 189, which without isolation was treated with cuprous oxide in DMF to yield 6S% of dithienothiophene (10) [Eq. (55)]. 

For each of these bonds, analyze the interactions of short range that determine its conformational behavior. Usually one finds that the torsion angles of the bonds in question and their adjoining bond angles can assume only relatively narrow domains and one identifies these domains with Rotational Isomeric States. The location of these states determines the geometry of those rotational isomers selected to represent the totality of conformations available to the macromolecule. 

J ADA Isomer Selection. Limited attention is often given in refineries to the isomer of ADA used (Lorton 1988). 2,6-ADA is a commonly used isomer, although it has been found inferior to 2,7-ADA in converting vanadium to its pentavalent form. If this conversion is not performed efficiently, elemental sulfur production rate will fall, and thiosulfate formation will increase. More attention to procuring only 2,7-ADA could augment the efficiency of the Stretford process. 

Table III shows that the selectivity is higher with rhodium than with cobalt in contrast to the case with methyl crotonate and methyl 3,3-di-methacrylate. Isomer selectivity is weak with Co2(CO)8, and the two isomeric aldehydes (9 and 10) are formed in nearly the same proportions. Aldehydes 7 and 8 are formed in very low yields but in the same proportions. With rhodium, 9 is the main product (38.9%) while 10 represents only 17.4% of the yield the threo and the erythro diastereo-isomers occur in 23.4 and 8.4% yields, respectively.

The data of Table VII show that the selectivity is poor with Co2 (CO) 8 and very high with rhodium. Aldehyde distribution shows an important orientation effect on the a carbon with respect to the ring. When rhodium is used, isomerization towards the methyl group is much more extensive than with propenylbenzene. When triphenylphosphine is used, isomer selectivity is essentially unchanged. In the presence of Co and Rh, reaction rates are lower than with propenylbenzenes this effect can be attributed to steric hindrance of the gem-dimethyl group. 

Z)-2-Phenyl-2-butene. (Z)-2-pheny 1-2-butene is not as stable as its (E) isomer. When Co >(CO)8 is used, results are the same with the (E) stereoisomer. However, when rhodium is used, isomer selectivity changes (Table VIII). The main isomeric aldehyde is the erythro di-astereoisomer which represents 33.9% of the whole mixture. Aldehyde 27 is formed in nearly the same ratio (32.9% ) while 6.8% and 4.4% of aldehyde 26 and the threo diastereoisomer are formed. 

With Rh, the phenomena are strikingly different since the aromatic ring does not influence the selectivity which is always very high, no matter what olefinic structure (except for 1,1-diphenylpropene). Isomer selectivity depends on several factors, mainly the structure and the stereochemistry of the alkenylbenzene. With conjugated alkenylbenzenes, addition of the CHO group occurs preferentially on the a carbon when the a and / carbons are monosubstituted. When the ft carbon is disubsti-tuted, because of steric requirements, hydroformylation is less selective and occurs on both the a and y carbon ... 

With nonconjugated alkenylbenzenes such as C6H5—CH2—CH=CH2 and C6H5—CH—CH=CH2, isomer selectivity is a function of substitutes... 

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