Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Cyclic reaction products

When the reactions of alkane molecules larger than the butanes or neopentane are studied, and in particular when the molecule is large enough to form a Cs or a Ce ring, the complexity of the reaction pathway is considerably increased and an important feature is the occurrence, in addition to isomerization product, of important amounts of cyclic reaction products, particularly methylcyclopentane, formed by dehydrocycliza-tion this suggests the existence of adsorbed cyclic species. The question is whether the reaction paths for dehydrocyclization and isomerization are related. There is convincing evidence that they are. Skeletal interconversions involving n-hexane, 2- and 3-methylpentane may be represented. [Pg.37]

From the preceding discussion, it can be seen that appropriate conditions must be maintained to maximize the 1 1 or 2 2 cyclization reactions. Cyclocondensations of two or four substrates (1 1 or 2 2 cyclizations) are favored in high dilution and with template cations. Often internal hydrogen bonding helps to favor the cyclic reaction product. A more complete discussion of cyclization versus polymerization in these polycondensation reactions in high-dilution conditions has been published (Fastrez, 1987). [Pg.85]

Asymmetric allylic amination of allylic carbonates, prepared from racemic MBH adducts, proceeds in the presence of the Pd catalyst chiral diamino-phosphine oxide (DIAPHOX) (292) and BSA to afford the corresponding chiral aza-MBH adduct derivatives 293 in excellent yield with up to 99% ee. The cyclic reaction products could be converted into various synthetically useful compounds, such as chiral cyclic p-amino acids (Scheme 3.119). ... [Pg.263]

Reyx, D. and Costes, B., Homopolymerisation of tetraglycidyl-4,4 diaminodiphenylmethane (TGDDM). Identification of cyclic reaction products. Polymer Commun., in press. [Pg.273]

Aaserud et al. reported an on-line coupling of SEC to Fourier transform mass spectrometry (FT-MS) using a modified commercial electron spray ionization (ESI) interface (Fig. 29) [169]. They analyzed a glycidyl methacrylate/butyl methacrylate copolymer with a broad molecular weight distribution, where fractionation and high resolving power were required for adequate characterization. The SEC/ESI/FT-MS also allowed for an unequivocal end-group determination and characterization of a secondary distribution due to the formation of cyclic reaction products. [Pg.47]

Two limiting cases may be distinguished In certain simple cases, particularly if cyclic reaction products are formed it is possible to assume that the new —C bonds are closed simultaneously. Such reactions could be properly described as w-complex multicenter processes (79). The linear polymerization of alkynes in which the new C—C bonds cannot be formed simultaneously may be considered the other extreme possibility, but it must also be expected that there are intermediate cases between these two types of reaction. In view of the generally nonspecific action of the catalysts any generalizations must be treated with caution. The reactions of alkynes and of norbornadiene with bis(acrylonitrile)-nickel and related complexes, however, appear to be simple enough to allow some mechanistic conclusions. [Pg.32]

Soon after the publication of Niederl and Vogel, it was Zinke in 1944 who isolated firom a reaction of a para-substituted phenol, viz. p-1,1,3,3-tetramethylbutyl phenol and formaldehyde a compound that had a molecular weight of 876 in agreement with a cyclotetrameric structure [11]. Not much later Comforth and his coworkers at the Shell - Laboratories in the UK found that the product reported by Zinke was not a single compound but a mixture of cyclic reaction products [12]. [Pg.5]

Figure 26.2 Liquid chromatograms, measured at the critical condition for linear polystyrene, of cyclization reaction products of dilute-solution ring closure of end-functionalized PS (solid lines) and their linear precursors (dotted lines) (Lee et al., 2000). The linear precursors elute at nearly identical times (5.4 min), independent of molecular weight. The major peak in the cyclic reaction product, marked Ring , elutes at times that increase with molecular weight. Note that all Ring products contain linear precursor impurities. (Reprinted with permission from H.C. Lee, H. Lee, W. Lee etal, Fractionation of cyclic polystyrene from linear precursor by HPLC at the chromatographic critical condition, Macw-molecules, 33, 8119-8121, 2000. 2000 American Chemical Society.)... Figure 26.2 Liquid chromatograms, measured at the critical condition for linear polystyrene, of cyclization reaction products of dilute-solution ring closure of end-functionalized PS (solid lines) and their linear precursors (dotted lines) (Lee et al., 2000). The linear precursors elute at nearly identical times (5.4 min), independent of molecular weight. The major peak in the cyclic reaction product, marked Ring , elutes at times that increase with molecular weight. Note that all Ring products contain linear precursor impurities. (Reprinted with permission from H.C. Lee, H. Lee, W. Lee etal, Fractionation of cyclic polystyrene from linear precursor by HPLC at the chromatographic critical condition, Macw-molecules, 33, 8119-8121, 2000. 2000 American Chemical Society.)...
Atoms and free radicals are highly reactive intermediates in the reaction mechanism and therefore play active roles. They are highly reactive because of their incomplete electron shells and are often able to react with stable molecules at ordinary temperatures. They produce new atoms and radicals that result in other reactions. As a consequence of their high reactivity, atoms and free radicals are present in reaction systems only at very low concentrations. They are often involved in reactions known as chain reactions. The reaction mechanisms involving the conversion of reactants to products can be a sequence of elementary steps. The intermediate steps disappear and only stable product molecules remain once these sequences are completed. These types of reactions are refeiTcd to as open sequence reactions because an active center is not reproduced in any other step of the sequence. There are no closed reaction cycles where a product of one elementary reaction is fed back to react with another species. Reversible reactions of the type A -i- B C -i- D are known as open sequence mechanisms. The chain reactions are classified as a closed sequence in which an active center is reproduced so that a cyclic reaction pattern is set up. In chain reaction mechanisms, one of the reaction intermediates is regenerated during one step of the reaction. This is then fed back to an earlier stage to react with other species so that a closed loop or... [Pg.16]

The reaction products formed by other nucleophilic reagents (e.g., amino compounds or carbanions derived from carbonyl or nitaro compounds) can be considered as ring chain prototropic systems. The newly formed C—or C—bond in the cyclic form of these compounds is more or less polar (evidence for this is the sensitivity to... [Pg.181]

Acidic hydrolysis of the amide group at pH 4.5 is a very slow reaction. Strong acidic conditions leads to a progressive insolubilization of the reaction product because of formation of cyclic imide structures ... [Pg.64]

Cycioaddition reaction (Sections 14.4, 30.6) A peri cyclic reaction in which two reactants add together in a single step to yield a cyclic product. The Diels-Alder reaction between a diene and a dienophile to give a cyclohexene is an example. [Pg.1239]

A special method, with only two examples, starts from 1,2,4-triazines.20 21 Diels-Alder reaction with the strained dienophile dimethyl tricyclo[4.2.2.02,5]deca-3,7,9-triene-7,8-dicarboxylate (14) is followed by an elimination of nitrogen via a retro-Diels-Alder process. The formed product, however, cannot be isolated, but reacts via another retro-Diels-Alder reaction and an electro-cyclic reaction to provide the azocine derivative 15. The sequence order of the reactions is not clear, but both pathways lead to the same product. [Pg.513]

In the case of the polymerization of n-butylsilane with Cp2ZrMe2, also a large percentage of cyclic Si5 and Si7 oligomers has been identified among the reaction products [163]. [Pg.32]

Cyclic sulphone Solvent Supporting electrolyte Alkylation agent after cleavage reaction Products Isolated yield... [Pg.1009]

The effect of the temperature on the polymerization of 53 in methylene chloride is presented in Table 3. The upper half of the data in the table shows the temperature effect on the products in the initial stage of the reaction, and the lower half is that for the middle to final stages of the reaction. Obviously there is a drastic change in the reaction products between -20 and -30 ° Below —30 °C, the cyclic dimer is the predominant or even sole product after the reaction of 48 hours, while above —20 °C, the low molecular weight polymer is exclusively formed. The cyclic oligomers once formed in the initial stage of the reaction are converted to the polymer in the later stage of the reaction above —20 °C. [Pg.65]

Time dependence of the reaction products can be seen more clearly in the time-yield curves of oligomerization in methylene chloride at —40° (Fig. 4). The yield of mixture of the cyclic tetramer and hexamer (mostly the latter), passed through a maximum value of about 40% and then decreased to nearly zero after 48 hours. On the other hand, the yield of the cyclic dimer increased rather sigmoidly with reaction time. [Pg.65]

Other evidence cited for SET mechanisms has been detection of radical or radical ion intermediates by ESR or CIDNP the finding that such reactions can take place at 1 -norbomyl bridgeheads and the formation of cyclic side products when the substrate has a double bond in the 5,6 position (such substrates are called radical probes). [Pg.403]


See other pages where Cyclic reaction products is mentioned: [Pg.43]    [Pg.51]    [Pg.61]    [Pg.14]    [Pg.819]    [Pg.2179]    [Pg.10]    [Pg.106]    [Pg.308]    [Pg.254]    [Pg.298]    [Pg.184]    [Pg.419]    [Pg.462]    [Pg.2179]    [Pg.89]    [Pg.43]    [Pg.51]    [Pg.61]    [Pg.14]    [Pg.819]    [Pg.2179]    [Pg.10]    [Pg.106]    [Pg.308]    [Pg.254]    [Pg.298]    [Pg.184]    [Pg.419]    [Pg.462]    [Pg.2179]    [Pg.89]    [Pg.311]    [Pg.14]    [Pg.465]    [Pg.468]    [Pg.23]    [Pg.264]    [Pg.187]    [Pg.88]    [Pg.473]    [Pg.294]    [Pg.340]    [Pg.9]    [Pg.159]    [Pg.155]    [Pg.62]    [Pg.35]   
See also in sourсe #XX -- [ Pg.106 ]




SEARCH



Cyclic reactions

Product studies cyclic ether reactions

© 2024 chempedia.info