Generation of Isomers

Given the efficient spiral algorithm for generation of isomer lists, many problems in structure and properties of higher fullerenes have been attacked. It is particularly important to have complete lists because it has turned out that possession of a closed... 

Manual generation of isomers, tested by three chemists (one Ph.D. and two graduate students) did not ve the correct result because of duplicates and omissions. 

Generation of Isomers of Organic Molecules Using Genetic Algorithms. 

Principle 6.2 (Par. 6.5.2) is readily applicable to the generation of isomers of single coronoids cf. Cyvin SJ (1992c), and Cyvin SJ, Cyvin and BrunvoU (1993e) on the analogous rules for benzenoids. 

In some cases the formation of a dioxolane or dioxan -can result in the generation of a new stereogenic center, either with complete selectivity or as a mixture of the two possible isomers. Since the new center is removed on deprotection, it should not seriously complicate the use of those protective groups that generate a new stereogenic center. 

Steric factors would ordinarily be expected to induce a preference for the larger group to move outward and thus generate the -isomer. It was observed, however, that in the case of l,2,3,4-tetrafluoro-tran5-3,4-bis(trifluoromethyl)cyclobutene, ring opening occurred with an inward rotation of the trifluoromethyl groups. ... 

Treatment of A -benzyltnfluoroacetimidoyl chloride with triethylamine in toluene at room temperature leads to in situ generation of trifluoroacetonitrile ben-zylide [4J] (equation 43), which reacts with methyl acrylate to form cycloadducts [43] (equation 44) Although the kinetic ratio of products favors the cis adduct (3 1), thermodynamic equilibration leads to an excess of the trans isomer (7 1). 

The close similarity in the isomer ratios obtained from different sources of the phenyl radical suggests that the mechanism of aryla-tion is independent of the nature of the reagent which generates the radical. This principle has been used in reverse in that the constancy of isomer ratios has been cited as evidence that the decomposition of lead tetrabenzoate gives free phenyl radicals. 

An earlier paper [PolG35] contained the essence of Polya s Theorem in its three-variable form, together with an informal proof of it. This paper also entered into the field of isomer enumeration by presenting a generating function for the substituted benzenes. 

H. Applications of artificial intelligence for chemical inference. XII. Exhaustive generation of cyclic and acyclic isomers. J. Am. Chem. Soc. 96 (1974) 7702-7714. 

The free radical catalyzed generation of valence isomers has been described to account for the products observed during the thermal re-... 

Alkoxyallylstannanes can be generated in situ by stannylation of allyl ethers or by 1,3-isomerization of isomers, and trapped by boron trifluoride-diethyl ether complex induced addition to aldehydes to give syn-diol derivatives 13,120. 3-Alkylthioallylstannanes can similarly be generated and trapped84. 

The first carbocationic photolysis to be investigated in detail was that of the tropylium ion (1) (van Tamelen et al., 1968, 1971), in which generation of the [3,2,0] valence bond isomer (the Dewar tropylium ion ), (2) was the dominant reaction. When irradiated for 10 minutes in 5% aqueous sulfuric acid, two major products were formed in a total... 

The phosphotriesterase from Pseudomonas diminuta was shown to catalyze the enantioselective hydrolysis of several racemic phosphates (21), the Sp isomer reacting faster than the Rp compound [65,66]. Further improvements using directed evolution were achieved by first carrying out a restricted alanine-scan [67] (i.e. at predetermined amino acid positions alanine was introduced). Whenever an effect on activity/ enantioselectivity was observed, the position was defined as a hot spot. Subsequently, randomization at several hot spots was performed, which led to the identification of several highly (S)- or (R)-selective mutants [66]. A similar procedure was applied to the generation of mutant phosphotriesterases as catalysts in the kinetic resolution of racemic phosphonates [68]. 

Finally, participation by a remote double bond in the solvolytic generation of a vinyl cation has also been observed recently (190). Solvolysis of cis and trans triflate, 234a and 234b, in trifluoroethanol buffered with lutidine gave, besides acyclic products, 20% cyclic products 235abc in the case of the cis triflate 234a and 35% cyclic products in the case of the trans isomer 234b (190). 

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