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Cyclic comparison

Application of combinatorial algorithms to random stepwise polymerization provides a buis for the understanding of the effect of ring formation on network structures and sol con sitions. A substantial portion of the sol is cyclic. Comparison with experimental data, such as ring fraction measurements ( ) or sol fraction analysis by GPC or HPLC, could be useful to verify the findings obtained in these computer simulation. The progreun can be e lsily adapted to other polycondensation reactions, and to cover the entire range of the polymerization process. [Pg.30]

Jones et al. [144,214] used direct dynamics with semiempirical electronic wave functions to study electron transfer in cyclic polyene radical cations. Semiempirical methods have the advantage that they are cheap, and so a number of trajectories can be run for up to 50 atoms. Accuracy is of course sacrificed in comparison to CASSCF techniques, but for many organic molecules semiempirical methods are known to perform adequately. [Pg.309]

Ton-exchange resins are used repeatedly in a cyclic manner over many years, and deterioration of both physical and chemical properties can be anticipated. Comparison of the properties of used resin with those of new resin is helpfiil to learning more about the nature and cause of deterioration (12). Corrective action frequendy extends the life of the resin. Comparison of properties must always be made with the resin in the same ionic form. [Pg.376]

Compressors have numerous forms, the exact configuration being based on the application. For comparison, the different types of compressors can be subdivided into two broad groups based on compression mode. There are two basic modes intermittent and continuous. The intermittent mode of compression is cyclic in nature, in that a specific quantity of gas IS ingested by the compressor, acted upon, and discharged, before the cycle is repeated. The continuous compression mode is one in which the gas is moved into the compressor, is acted upon, moved through the compressor, and discharged without interruption of the tlnv. at any point in the process. [Pg.2]

Fig. 1.6. Charge distributions in strained cyclic hydrocarbons in comparison with cyclohexane. Data are from K. B. Wiherg, R. F. W. Bader, and C. D. H. Lau, J. Am. Chem. Soc. 109 1001 (1987). Fig. 1.6. Charge distributions in strained cyclic hydrocarbons in comparison with cyclohexane. Data are from K. B. Wiherg, R. F. W. Bader, and C. D. H. Lau, J. Am. Chem. Soc. 109 1001 (1987).
Table I.IS gives total bonding energies in kilocalories per mole for some simple molecules. The B3iyP results are comparable in accuracy to G1 and G2 results. Another comparison was done with a series of cyclic hydrocarbons as the test case. The calculations were done using an isodesmic reaction scheme. The results are given in Table 1.19. Density functional calculations have also been successfully extended to functionalized molecules. ... Table I.IS gives total bonding energies in kilocalories per mole for some simple molecules. The B3iyP results are comparable in accuracy to G1 and G2 results. Another comparison was done with a series of cyclic hydrocarbons as the test case. The calculations were done using an isodesmic reaction scheme. The results are given in Table 1.19. Density functional calculations have also been successfully extended to functionalized molecules. ...
Bradshaw and his coworkers have listed several motivations for their explorations in this area. One objective of [the] research program is to prepare and study a series of multi-dentate compounds which resemble naturally occurring macrocyclic compounds . Further, Bradshaw and his coworkers have said that it is our hope that we can prepare macrocycles to mimic the selectivities of the naturally occurring cyclic antibiotics and thereby make available models for the investigation of biological cation transportation and selectivity processes . These workers have presented a number of comparisons with valinomy-cin . The other expressly stated goal of their research is to prepare molecules which will allow us to systematically examine the parameters which affect complex stability and to understand that stability in terms of AH and TAS values for complex formation . [Pg.220]

Chiomatograirilic methods often devdop in a cyclic manner The discovery of a new separation technique naturally stimulates interest concerning the method this attention wanes when another technique appears on the horizon and soon interest is directed at the new technique. There is then a confrontation between the methods and a critical comparison of the advantages and disadvantages of the two m hods. This sometimes leads to a renaissance of the older method, which has been the subject of further development in the meantime. In this context discover-les made in connection with the modem technique are often used to advantage in / the older one... [Pg.469]

Nuclear magnetic resonance has revolutionized structure determination of iminium salts. A compilation of various resonances for acyclic and cyclic iminium salts are given in Tables 3 and 4 for comparison purposes and for determination of trends. It should be noted that the simplest symmetrically... [Pg.177]

Chemical Shifts S of the Cyclic Protons in the h NMR Spectra of 1,2,4-Triazines AND Their W-Oxides in CDCI3 (A) or DMSO- Is (B) in Comparison (A ) with Those of the Parent 1, 2,4-Triazines... [Pg.263]

Fig. 3-3. Comparison of the values of enantiomeric resolution of different DNP-D,L-amino acids at different deconvolution stages of a cyclic hexapeptide sublibrary. Resolution values in a cyclo(Arg-Lys-X-X-X-P-Ala) sublibrary, in the first line, are compared to those obtained in sublibraries with a progressively increasing number of defined positions. All the sublibraries were 30 mM in the running buffer while the completely defined cyclo(Arg-Lys-Tyr-P-Tyr-P-Ala) peptide is used at 10 mM concentration. Conditions cyclopeptide sublibrary in 20 mM sodium phosphate buffer, pH 7.0 capillary, 50 pm i.d., 65 cm total length, 57 cm to the window V = -20 kV, I = 40 electrokinetic injection, -10 kV, 3 s detection at 340 nm. (Reprinted with permission from ref. [75]. Copyright 1998, American Chemical Society.)... Fig. 3-3. Comparison of the values of enantiomeric resolution of different DNP-D,L-amino acids at different deconvolution stages of a cyclic hexapeptide sublibrary. Resolution values in a cyclo(Arg-Lys-X-X-X-P-Ala) sublibrary, in the first line, are compared to those obtained in sublibraries with a progressively increasing number of defined positions. All the sublibraries were 30 mM in the running buffer while the completely defined cyclo(Arg-Lys-Tyr-P-Tyr-P-Ala) peptide is used at 10 mM concentration. Conditions cyclopeptide sublibrary in 20 mM sodium phosphate buffer, pH 7.0 capillary, 50 pm i.d., 65 cm total length, 57 cm to the window V = -20 kV, I = 40 electrokinetic injection, -10 kV, 3 s detection at 340 nm. (Reprinted with permission from ref. [75]. Copyright 1998, American Chemical Society.)...
To extend the scope of asymmetric transannular C-H insertions, more highly functionalized medium-sized cyclic epoxides have been investigated. A triad of cydooctene oxides 34, 36, and 38, possessing protected diol units, gave the expected alcohols 35, 37, and 39 (Scheme 5.10) [17, 18] an asymmetric synthesis of (-)-xialenon A has been achieved starting from alcohol 39 [19]. In comparison,... [Pg.150]

A comparison of the cationic polymerization of 2,3-dihydrofurans with that of furan and 2-alkylfurans shows that the complications of the latters two, arising from the dienic character of the monomers, obviously vanish when the monomer is a simple cyclic vinyl ether with just one reactive site, viz. the carbon-carbon double bond. However, it also points out that ring opening in the polymerization of furans by acidic catalysts in the absence of water is unlikely, because otherwise it would also occur to some degree in the polymerization of dihydrofurans. [Pg.66]

Many anodic oxidations involve an ECE pathway. For example, the neurotransmitter epinephrine can be oxidized to its quinone, which proceeds via cyclization to leukoadrenochrome. The latter can rapidly undergo electron transfer to form adrenochrome (5). The electrochemical oxidation of aniline is another classical example of an ECE pathway (6). The cation radical thus formed rapidly undergoes a dimerization reaction to yield an easily oxidized p-aminodiphenylamine product. Another example (of industrial relevance) is the reductive coupling of activated olefins to yield a radical anion, which reacts with the parent olefin to give a reducible dimer (7). If the chemical step is very fast (in comparison to the electron-transfer process), the system will behave as an EE mechanism (of two successive charge-transfer steps). Table 2-1 summarizes common electrochemical mechanisms involving coupled chemical reactions. Powerful cyclic voltammetric computational simulators, exploring the behavior of virtually any user-specific mechanism, have... [Pg.35]

Table 9 shows the PP MO results for this interesting series of highly strained three-membered cyclic molecules. Here a detailed comparison is possible with the best results of an all-electron study, including d functions10 (also reported in Table 9). An analysis of this table reveals how all trends in population analysis, both in charges and overlap populations, are the same in the AE + d and in the simple PP calculations, with very few and very minor exceptions. PP predicts a charge donation to the aliphatic groups, while AE predicts a withdrawal, mainly due to the availability of d orbitals on sulphur, which can allocate extra electronic charge. As outlined in the general notes on population analysis (Section III.D) comparisons should be carried out on a relative basis and,... Table 9 shows the PP MO results for this interesting series of highly strained three-membered cyclic molecules. Here a detailed comparison is possible with the best results of an all-electron study, including d functions10 (also reported in Table 9). An analysis of this table reveals how all trends in population analysis, both in charges and overlap populations, are the same in the AE + d and in the simple PP calculations, with very few and very minor exceptions. PP predicts a charge donation to the aliphatic groups, while AE predicts a withdrawal, mainly due to the availability of d orbitals on sulphur, which can allocate extra electronic charge. As outlined in the general notes on population analysis (Section III.D) comparisons should be carried out on a relative basis and,...
The less strain energy inherent in the four-membered ring sulfoxides and sulfones, their less distorted geometries and the lack of potential aromatic -type conjugation effects make the comparison of their physical and chemical properties with other cyclic and... [Pg.429]

A useful comparison of the 13C shifts for acyclic and cyclic five- and six-membered sulfur compounds has been made86,220, but data on cyclic sulfur compounds of other ring sizes are rather limited. Typically, oxidation of sulfide to a sulfone results in 20-25 ppm... [Pg.440]

Kinetic studies using 1,9-decadiene and 1,5-hexadiene in comparison widi catalyst 14 and catalyst 12 demonstrate an order-of-magnitude difference in their rates of polymerization, widi 14 being the faster of the two.12 Furdier, this study shows diat different products are produced when die two catalysts are reacted widi 1,5-hexadiene. Catalyst 14 generates principally lineal" polymer with the small amount of cyclics normally observed in step condensation chemistry, while 12 produces only small amounts of linear oligomers widi die major product being cyclics such as 1,5-cyclooctadiene.12 Catalyst 12, a late transition metal benzylidene (carbene), has vastly different steric and electronic factors compared to catalyst 14, an early transition metal alkylidene. Since die results were observed after extended reaction time periods and no catalyst quenching or kinetic product isolation was performed, this anomaly is attributed to mechanistic differences between diese two catalysts under identical reaction conditions. [Pg.438]


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See also in sourсe #XX -- [ Pg.55 ]




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Extraction of Electron Transfer Kinetics from Cyclic Voltammetric Signals. Comparison with Other Techniques

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