Where results make sense

About us   |   Why use us?   |   Reviews   |   PR   |   Contact us

[No title]   (Site not responding. Last check: 2007-10-07) Oxonium ion ladders Although the presence of multiple oxonium ions found in the spectrum can be taken into account, the additional confidence that logical patterns within the oxonium ion peaks themselves provides is also reasonable to score, as they can be seen as lowering the likelihood that the individual peaks are random events. Function for oxonium ions evaluation In one embodiment the invention provides for oxonium ion presence to be assessed by summing scores representing oxonium ion presence, oxonium ion ladder presence, and peak density found in a spectrum, as well as a score evaluating of the set of all oxonium ion peaks found in the spectrum. For an oxonium ion representing a di-or tri-saccharide observed along with oxonium ions that represent its component monosaccharides, a constant factor of P is also added to the score. www.wipo.int /cgi-pct/guest/getbykey5?KEY=04/61407.041007&ELEMENT_SET=DECL   (12426 words)

Novel initiators for cationic polymerization - Patent 5084586   (Site not responding. Last check: 2007-10-07) Iodonium, oxonium, sulfonium, sulfoxonium, and various other onium salts are well known in the art, particularly as initiators of cationic and free radical polymerization. Additionally, oxonium salts may also be prepared by using perfluoroalkanesulfonated Lewis acid-ether adducts in the presence of epichlorohydrin via the intermediacy of an inner oxonium salt similar to procedures known in the art to incorporate the perfluorinated anions in the oxonium salts (see Meerwein, H.; Battenberg, E.; Gold, H.; Pfeil, E.; William, G. Prakt. The auxiliary conditions used in conjunction with certain cations is well known in the art, such as, for example, the use of heat in conjunction with oxonium cations and the use of actinic radiation and a photosensitizer in conjunction with iodonium cations. www.freepatentsonline.com /5084586.html   (5586 words)

Hydronium -- Facts, Info, and Encyclopedia article   (Site not responding. Last check: 2007-10-07) According to IUPAC ion nomenclature, it should be referred to as "oxonium." Hydroxonium may also be used unambiguously to identify this ion. A draft (additional info and facts about IUPAC) IUPAC proposal recommends the use of oxonium and oxidanium in organic and inorganic chemistry contexts, respectively. These hydrons do not exist in a free state: they are extremely reactive and are (additional info and facts about solvated) solvated by water. www.absoluteastronomy.com /encyclopedia/h/hy/hydronium.htm   (608 words)

ILL : ANNUAL REPORT 2001 Oxonium ions, forms of the hydrated proton, have been known for many years [1,2] but their formation, isolation and study has often been a rather serendipitous process. Thus, crown ethers are remarkably effective in the isolation of strong hydrogen bond acceptors such as the hydrated proton (oxonium ion) [2]. This suggests that the positive charge of the oxonium ion is stabilised by interactions to the crown ether. www.ill.fr /AR-01/p-40.htm   (1038 words)

Cyclic Oxonium Ions and Related Structures -- Gargiulo and Tarbell 62 (1): 52 -- Proceedings of the National Academy of ... oxonium salts have been prepared, isolated, and characterized as crystalline solids: the 1,2,5-trimethyltetrahydrofuranium (IIa), the 1,2,2,5-tetramethyl (IIb), the trans-1-methylperhydrobenzofuranium (IVa), the trans-1,2-dimethyl (IVb), and the trans-1,2,2-trimethyl (IVc) compounds. Further evidence for the cyclic structure is given by the identification of 2,2,5-trimethyltetrahydrofuran (VIII) from the action of pyridine and lithium chloride on the 1,2,2,5-tetramethyltetrahydrofuranium salt IIb. Solvolysis of this salt by ethanol gave 2-ethoxy-2-methyl-5-methoxyhexane (VII) by attack at the tertiary carbon of the oxonium ion. www.pnas.org /cgi/content/abstract/62/1/52   (271 words)

Decomposition of cumene hydroperoxide using a stable carbonium, tropylium or oxonium salt as the catalyst - Patent ... Cumene hydroperoxide is decomposed to phenol and acetone using an isolable carbonium, tropylium or oxonium salt as the catalyst. This invention relates to the catalytic cleavage of cumene hydroperoxide to equal molar portions of phenol and acetone in the presence of a relatively stable, isolable carbonium, tropylium or oxonium salt, such as the tetrafluoborate, as the catalyst. A particular advantage in the use of the carbonium, tropylium or oxonium salt decomposition catalysts of this invention is that a selectivity greater than 95 percent, approaching 100 percent under optimum conditions, can be obtained. www.freepatentsonline.com /4209465.html   (3062 words)

Process for making macromolecular monomers of polylactones with terminal acryloyl unsaturation and block copolymers ... The process of claim 1 wherein said oxonium salt is a trialkyl oxonium salt selected from the group consisting of triethyloxonium hexafluorophosphate, triethyloxonium hexafluoroantimonate, triethyloxonium hexafluoroarsenate, triethyloxonium hexachloroantimonate, and triethyloxonium tetrafluoroborate, wherein alkyl is lower C.sub.1 -C.sub.6 alkyl. Despite use of such a strong oxonium salt catalyst, there is essentially no formation of a di(meth)acrylic species formed by interesterification, no formation of cyclic oligomers, and the ethylenic double bond of the alcohol does not undergo carbocationic polymerization under the acidic conditions required for the cationic ring-opening polymerization of the lactone used. It is most preferred to use a cyclic or acyclic oxonium salt which may be secondary or tertiary, for example, an oxonium salt selected from the group consisting of triethyloxonium hexafluorophosphate, triethyloxonium hexafluoroantimonate, triethyloxonium hexafluoroarsenate, triethyloxonium hexachloroantimonate, and triethyloxonium tetrafluoroborate. www.freepatentsonline.com /4983689.html   (7271 words)

c:\\ work\\ winter91\\ final.   (Site not responding. Last check: 2007-10-07) The old scheme, illustrated above, involves methylation of an oxonium ylide: a methyloxonium species (1) is deprotonated to make methyleneoxonium ylide (2), which is then rapidly methylated by a second methyloxonium equivalent, forming the CC bond and yielding ethyloxonium (3). It is from these intermediates, rather than from the oxonium ylide in the previous scheme, that further methylation by the second methyloxonium equivalent forms the initial CC bond (7). The data for the CO catalyzed mechanism proposed by Jackson and Bertsch is shown in the upper half of the graph; the lower half reports the data for the previous mechanism. www.lct.jussieu.fr /manuals/Programmes/Gaussian98/userprof.htm   (648 words)

Block copolyethers via oxonium coupling of poly(tetramethylene ether) glycols - Patent 5284980   (Site not responding. Last check: 2007-10-07) This coupling reaction proceeds through the formation of tertiary oxonium ions which are generated in a poly(tetramethylene ether) glycol depolymerization step in the presence of appropriate catalyst. The lower threshold for the formation of block copolyethers via oxonium coupling poly(tetramethylene ether) glycols with other diols, triols and polyols is a reaction temperature of about 85.degree. The tertiary oxonium species react rapidly with diols or polyols to increase the overall molecular weight yielding the modified segmented end or block structures. www.freepatentsonline.com /5284980.html   (2297 words)

Lysozyme Binding & Catalysis   (Site not responding. Last check: 2007-10-07) The cleavage of the glycosidic bond between the substrate D and E rings occurs through protonation of the bridge oxygen atom by Glu 35. The resulting D-ring oxonium ion is stabilized by the proximity of the Asp 52 carboxylate group and the enzyme-induced distortion of the D ring. The oxonium ion transition state of the D ring in the lysozyme reaction is stabilized by resonance. www.bio.cmu.edu /courses/03231/LecF04/Lec28/LysoMech.html   (179 words)

Part IA. Introduction   (Site not responding. Last check: 2007-10-07) In this research, we are investigating oxonium ylides or complexes formed by interactions of singlet carbenes with water, selected alcohols, and dimethylether at the RHF and MP2 levels of theory using 3-21G, 6-31G*, and 6-311G** basis sets. Previous theoretical work on oxonium ylides and complexes has focused primarily on the interaction between water and methylene [1-3]. In addition to studying the structure and energetics of oxonium ylides or complexes formed between singlet carbenes and alcohols or ethers, we are investigating the reactivity of the complexes by determining transition states and intermediates along the reaction path for the addition of the carbene complex to ethene. www.ch.ic.ac.uk /ectoc/papers/72/pt1intro.html   (502 words)

Evidence for Reversible Ylide Formation: Equilibrium between Free Alkylidenecarbenes and Ethereal ...   (Site not responding. Last check: 2007-10-07) Reactions were observed to be temperature dependent, as reflected in variations in the product profiles: decreasing the reaction temperature tended to decrease the yields of free alkylidenecarbene-derived products, i.e., cyclopentenes, alkynes, and vinylammonium salts, and to increase those of the vinyloxonium ylide-derived products, vinyl ethers. This temperature dependence is explained in terms of reversible oxonium ylide formation. No evidence was observed to suggest the existence of an equilibrium between the free alkylidenecarbene and the sulfonium ylide in the reaction in tetrahydrothiophene. pubs.acs.org /subscribe/journals/jacsat/118/i42/abs/ja961797q.html   (198 words)

Asymmetric Induction via an Intramolecular Haloetherification Reaction of Chiral Ene Acetals Nucleophilic addition to a carbocation or an oxonium ion, formed by a C-O bond fission of an acetal, has been recognized as a useful synthetic tool in organic chemistry, and many variants have been developed so far. The cis-ene acetal 19a, readily synthesized as a single isomer in 93% yield from 16 and 17a, was subjected to an intramolecular haloetherification to give the mixed acetal 20a via an oxonium ion intermediate (refer to intermediate E in Scheme 9). They suggested that the formation of the 6-membered oxonium ion was slower than that of the 5-membered one (see ref. 4d). www.ch.ic.ac.uk /ectoc/echet98/pub/011   (4364 words)

I. Introduction   (Site not responding. Last check: 2007-10-07) It is generally the case that oxonium ylides are less stable than their nitrogen-, sulfur-, or phosphorous-containing ylides [1-3]. Experimental evidence for the existence of the simplest oxonium ylide, H2O-CH2, formed between singlet methylene and water, includes observation of an intermediate in the gas phase reaction between water and methylene, with a lifetime of approximately one microsecond [4]. Experimental evidence also exists which indicates the formation of oxonium ylides in reactions of singlet carbenes with alcohols and ethers in solution [8-11]. www1.elsevier.com /homepage/saa/eccc3/paper41/intro.html   (527 words)

Fragmentation of compounds Aldehydes and Ketones: The predominate cleavage in aldehydes and ketones is loss of one of the side-chains to generate the substituted oxonium ion. For carboxylic acids and unsubstituted amides, characteristic peaks at m/e = 45 and 44 are also often observed. For primary alcohols, this generates a peak at m/e = 31; secondary alcohols generate peaks with m/e = 45, 59, 73, etc., according to substitution. www.ivv.fraunhofer.de /ms/ms-ion_fragmentation_2.html   (472 words)

Substitution-Transfer-Abstraction-Displacement Oxonium ion, [OH is the conjugate Brønsted acid The oxonium ion, [OH is the Brønsted acidic species in all aqueous Brønsted acid solutions. Note that oxonium chloride OH Cl is the oxygen analogue of ammonium chloride, NH Cl. Both are type 11 Lewis acid/base complexes, here. www.meta-synthesis.com /webbook/21_stad/stad.html   (2731 words)

Reaction - Acidic reaction [www.lgflhome.net] The molecule of acetic acid is able to transfer one of its protons to the water molecule. In this way the equilibrium will be shifted in favour of oxonium ions. The more acetic acid can be found in the water, the more oxonium ion is produced, and hence the more the solution will be acid. www.lgflhome.net /celebrate/community/celebrate/resources/Hungary/leangol/Reaction/Savas   (91 words)

CHM 453-00   (Site not responding. Last check: 2007-10-07) The breakdown of glycogen to glucose-1-phosphateinvolves the intermediacy of an oxonium ion of glucose. The synthesis of glycogen from glucose-1-phosphate also involves the intermediacy of an oxonium ion of glucose. Choose to draw the mechanism ofEITHER, the reaction catalyzed by glycogen phosphorylaseOR the mechanism of the reaction catalyzed by UTP-glycogen synthase. www.muhlenberg.edu /depts/chemistry/chem453/Keyex2.html   (1729 words)

A Density Functional Study of Trigold Oxonium Complexes and of Their Dimerization   (Site not responding. Last check: 2007-10-07) The dimerization of trigold oxonium cations has been studied theoretically by means of the all-electron scalar relativistic linear combination of Gaussian-type orbitals density functional (LCGTO-DF) approach. Additionally, the influence of the steric repulsion of larger phosphine substituents on the structure of the dimer has been examined using a force field method. Reflecting the competition between the Au-Au attraction and the interligand steric repulsion, in agreement with the experimental trends, the dimerization in a locally tetrahedral coordination is favored for the nonligated trigold oxonium cations, whereas a locally rectangular coordination is obtained for the phosphine-ligated complexes. pubs.acs.org /cgi-bin/abstract.cgi/inocaj/1996/35/i18/abs/ic960418r.html   (178 words)

[No title]   (Site not responding. Last check: 2007-10-07) The oxonium ion, being a chemically reactive intermediate, could either react once formed with a phenol to give the phenyl ether, or by It may be that under these conditions the oxonium ion is stabilised and therefore less likely form the by-product. Hence at any one time there are larger quantities of nucleophile available to react with the intermediate oxonium species. www.wipo.int /cgi-pct/guest/getbykey5?KEY=01/04123.010118&ELEMENT_SET=DECL   (3113 words)

Onium Ions -- Books   (Site not responding. Last check: 2007-10-07) They consider well-established classes such as azonium, oxonium, sulfonium, selenonium, telluronium, and phosphonium but also include more recent types such as siliconium, halonium, carbonium, carboxonium, carbosulfonium, and carbazonium. Discussions of well-established classes of onium ions, such as azonium, oxonium, sulfonium, selenonium, telluronium, and phosphonium ions. Chapters discuss general Aspects and Scope, Azonium Ions, Oxonium Ions, Sulfonium Ions, Carbonium Ions, Siliconium Ions, Phosponium and Arsonium Ions, Halonium Ions and Onium Dications. cadgate.com /book/un/471148776   (678 words)

Medline Publication: Alkynyliodonium salts in organic synthesis. Dihydrofuran formation via a formal stevens shift of a ... Dihydrofuran formation via a formal stevens shift of a carbon substituent within a disubstituted-carbon oxonium ylide. A putative 1,2-group shift within an unsaturated oxonium ylide (Stevens rearrangement) accounts for the oxygen-to-carbon transfer of the ether substituent. Deuterium labeling studies clarify the mechanistic course of this shift by providing evidence consistent with intramolecular substituent transfer and by identifying the primary source of the proton that intercepts the ylide in the major yield-limiting process. www.fred.psu.edu /ds/retrieve/fred/medlinepub/11112587   (133 words)

World War 1 and 2 - Fischer esterification   (Site not responding. Last check: 2007-10-07) Proton transfer from the oxonium ion to a second molecule of alcohol gives a TCAC Proton transfer from one of the hydroxyl groups of the TCAC gives a new oxonium ion. Loss of water from this oxonium ion gives the ester and water www.worldwardiary.com /history/Fischer_esterification   (121 words)

[No title] The formed oxonium ion dissociates from the alkyl constituent in a rate-determining step that forms the carbocation for the reaction and a water molecule. After dissociation of the oxonium ion from the alkyl group, the carbocation, a Bronsted acid, reacts readily with water, a Bronsted base, through donation of an H+ proton. The result of this interaction is the transfer of electrons from Oxygen’s lone pair to the H+ ion, and the resulting transfer of electrons to the positively charged carbon of the carbocation. www.people.virginia.edu /~tw8h/241/Exp7revised.doc   (4803 words)

page3 resonance-stabilized oxonium ion at C1, called the oxocarbonium ion. residue with the polysaccharide, leaving an enzyme-stabilized oxonium ion. oxonium ion so that H2O will attact from the inside that allows retention of configuration. members.aol.com /wests100/page3.html   (553 words)

USC Chemweb: Professor George A. Olah When they are used as solvents in ion-generating reactions, the lifetimes of carbocations and onium ions (halonium, oxonium, etc.) are sufficiently long to allow them to be examined by a variety of chemical and spectroscopic techniques ( New types of oxonium, halonium and other onium ions were prepared and studied. The role of electrophilic (protic) solvation of the non-bonded electron pairs in oxonium ions (superelectrophilic activation) is widely explored, allowing new applications in alkylation, acylation and related reactions. chem.usc.edu /faculty/Olah.html   (854 words)

Information Archive at NNYTech   (Site not responding. Last check: 2007-10-07) In carbon monoxide, or at least its ground state, both the C and the O are tetravalent, with 3 covalent bonds and one ionic bond. The carbon, bearing the negative charge, is effectively a carbanion; the oxygen, bearing the positive charge, is effectively an oxonium ion: (-)C[triple covalent bond]O(+). To achieve this, and similarly in tertiary oxonium salts, the oxygen has to lose an electron; or, in tertiary oxonium salts, at least combine with a positively-charged carbonium ion (e.g. logan.nnytech.net /sgroup/thechemistrycluster/3890/1   (303 words)

The mechanism of alkene elimination from the oxonium ions (CH3CH2)2C=OH+, ... The mechanism of alkene elimination from these oxonium ions is discussed in the light of earlier studies on the behaviour of their lower homologues, (CH and CH, which eliminate ethylene.Propene loss from (CH must entail skeletal rearrangement leading to CH The first two possibilities involve 1,2-H shifts in conjunction with ring-closures to either protonated oxiranes or oxetanes, followed by ring- opening in the opposite sense, thus breaking the original C-O bond and allowing the hydroxy function to migrate along the carbon chain. Alternatively, a combination of 1,2-H and 1,2-alkyl shifts permits the carbon skeleton to be isomerised via the isomeric oxonium ion, CH www.impub.co.uk /abs/EMS01_0033.html   (272 words)

answer key, 3311 mid-term 2, Fall 2001, M. Asirvatham (A) The simultaneous loss of a b-hydrogen and water from the oxonium ion. (B) Protonation of the alcohol to form an oxonium ion. (C) Loss of water from the oxonium ion to form a carbocation. orgchem.colorado.edu /examarchives/11MAF01/imagesmaex2/MA11F01mt2ans.html   (475 words)

Try your search on: Qwika (all wikis)

About us   |   Why use us?   |   Reviews   |   Press   |   Contact us   Copyright © 2005-2007 www.factbites.com Usage implies agreement with terms.