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  • Articles: DFG German National Licenses  (17)
  • 1995-1999  (11)
  • 1960-1964  (6)
  • 1890-1899
  • Reaction mechanisms
  • 1
    Electronic Resource
    Electronic Resource
    Preparation of 2,3,5-Tri-O-benzyl-4-thio-L-arabino-furanosides and the Corresponding 4′-Thionucleoside Analogues (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 691-696 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; 4-Thiofuranosides ; Nucleosides ; Reaction mechanisms ; NOE measurements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -1-O-Acetyl-2,3,5-tri-O-benzyl-4-thio-L-arabino-furanose (9) has been prepared from D-xylose via the 1,4-dithio-L-arabino-furanoside 8. The crucial step of the reaction, i.e. the intramolecular cyclization of the open-chain dithioacetal 5, has been achieved in a yield of 90% by applying tetrabutylammonium iodide as promoter. Reaction of 9 with bis(trimethylsilyl)uracil or -thymine led to the benzyl derivatives 12 and 13 from which the deprotected 4′-thionucleoside analogues 14 and 15 have been prepared by debenzylation with boron tribromide.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Modern valence-bond description of chemical reaction mechanisms: the 1,3-dipolar addition of fulminic acid to ethyne (1998)
    Springer
    Theoretical chemistry accounts 100 (1998), S. 222-229 
    Details
    ISSN: 1432-2234
    Keywords: Key words: Spin-coupled approach ; 1 ; 3-Dipolar cycloadditions ; Reaction mechanisms ; Valence-bond theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. The electronic mechanism for the gas-phase 1,3-dipolar cycloaddition of fulminic acid (HCNO) to ethyne is studied through a combination of modern valence-bond theory in its spin-coupled (SC) form and intrinsic reaction coordinate calculations utilizing a complete-active-space self-consistent field wavefunction. It is shown that the concerted reaction follows a “heterolytic” route, during which three orbital pairs corresponding to three distinct bonds in the reactants (an in-plane π bond in ethyne, and a C-N and an N-O in-plane bond in HCNO) shift simultaneously to create the two new bonds closing the isoxazole ring and a nitrogen lone pair. The analysis of the SC wavefunction strongly suggests that the reacting system remains nonaromatic throughout the most important part of the cycloaddition process. This investigation provides the first demonstration of an alternative SC description of a bond rearrangement, achieved through the movement of singlet orbital pairs through space, during which at least one of the orbitals within a pair becomes completely detached from the atomic centre with which it is associated initially and ends up localized about another centre.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002140050383
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  • 3
    Electronic Resource
    Electronic Resource
    Reply to further comments on enzymes of the xanthine oxidase family (1998)
    Springer
    JBIC 3 (1998), S. 559-560 
    Details
    ISSN: 1432-1327
    Keywords: Key wordsXanthine oxidase ; Molybdenum enzymes ; Reaction mechanisms ; Electron paramagnetic resonance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050268
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  • 4
    Electronic Resource
    Electronic Resource
    Bismuth(III) Trifluoromethanesulfonate: A Chameleon Catalyst for the Friedel-Crafts Acylation (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2743-2746 
    Details
    ISSN: 1434-193X
    Keywords: Arenes ; Benzene ; Toluene ; Chlorobenzene ; Benzoylation ; Acylations ; Reaction mechanisms ; Bismuth trifluoromethanesulfonate ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A mechanism for acylations catalyzed by bismuth(III) triflate (1) is proposed in the case of the benzoylation of benzene, toluene, and chlorobenzene. With Bz2O as a reagent, 1 acts as a Lewis acid and allows the benzoylation of toluene. It is almost completely recovered after the reaction. With BzCl, 1 promotes an exchange reaction which generates BzOTf, which is the active species of the benzoylation. In this latter case, the reaction leads to the formation of TfOH which finally reacts with BiCl3 to partially regenerate 1. The power of the Bz2O/1 system is less than that of BzCl/1, which allows not only the benzoylation of toluene but also that of benzene and deactivated chlorobenzene. The activity of 1 is much higher than that of other metallic triflates previously reported, and is comparable with that of TfOH, however it also has the advantage that the triflate moieties are more easily recoverable.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    An Unorthodox Pathway to the 1,2-Dithiin SystemDedicated to Professor Wolfgang Beck, München, on the occasion of his 65th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1677-1684 
    Details
    ISSN: 0947-3440
    Keywords: 1,2-Dithiin ; Cycloadditions ; Sulfur extrusion ; Thiophenes ; Reaction mechanisms ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tetracyanoethylene combines with two molecules of thiobenzophenone in refluxing benzene to give the tetrasubstituted 1,2-dithiin 8 (21-29%) besides the corresponding thiophene derivative 9 (40-52%). The X-ray analysis of the ruby-red 8 reveals a half-chair conformation with a torsion angle of 58.9° at the disulfide bond. The thermal desulfurization 8 → 9 (benzonitrile, 100°C) proceeds with t1/2 = 26.7 h, whereas the sulfur loss induced by triethyl phosphite is a billion times faster. The mechanisms of the formation of 8 and its sulfur extrusion are discussed in the light or recent literature.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970808
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  • 6
    Electronic Resource
    Electronic Resource
    Flash Pyrolysis of 1,1,1-Trimethyltetrasilane - Evidence for the Formation of Dibridged Si2H2 (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 1043-1046 
    Details
    ISSN: 0009-2940
    Keywords: Matrix isolation ; Ab initio calculations ; Oligosilanes ; Silicon atoms ; Reaction mechanisms ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pulsed flash pyrolysis of 1,1,l-trimethyltetrasilane (5) led to trimethylsilane, silane and a further species which is believed to be dibridged Si2H2 (13). Another route to 13 was found in the cocondensation of hydrogen and silicon atoms in an argon matrix at 12 K. The identification of matrix-isolated 13 is based on observed IR bands at 1475.6, 1092.8 and 890.3 cm-1. These positions are in good agreement with the ab initio calculated wavenumbers for the strongest absorptions of 13. The band shifts for the mono- and dideuterated isotopomers support this assignment.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971300804
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  • 7
    Electronic Resource
    Electronic Resource
    Uncatalyzed Transfer Hydrogenation and Transfer Hydrogenolysis: Two Novel Types of Hydrogen-Transfer ReactionsDedicated to Professor Paul D. Bartlett on the occasion of his 90th birthday (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 36 (1997), S. 1406-1430 
    Details
    ISSN: 0570-0833
    Keywords: arenes ; coal liquefaction ; hydrogenations ; radical reactions ; reaction mechanisms ; Arenes ; Coal liquefaction ; Hydrogenation ; Radical reactions ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Uncatalyzed transfer hydrogenations are H2-transfer reactions in which donors that contain weakly bound hydrogen atoms undergo an H-atom transfer (retrodisproportionation) onto an acceptor containing unsaturated bonds such as C=C, C=O, C=N, N=N, N=O. Transfer hydrogenolyses are reactions in which σ bonds are cleaved upon additon of H2. These hydrogenations are terminated by H, transfer; they do not follow a radical-chain mechanism. The initial steps of both types of reactions, H-atom transfer, complement the bimolecular formation of 1,4-diradicals from alkenes or heteroalkenes within the scope of bimolecular radical formation (Molecule-Induced Radical Formation, MIRF). The title reactions play an important role in coal liquefaction, aromatization reactions with nitroarenes or quinones, and possibly biochemical dehydrogenations. This review focuses on mechanistic studies, structure-reactivity relationships, and current applications of these reactions.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199714061
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  • 8
    Electronic Resource
    Electronic Resource
    Unifying the Current Data on the Mechanism of Cleavage-Transesterification of RNA (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 36 (1997), S. 432-450 
    Details
    ISSN: 0570-0833
    Keywords: hydrolysis ; kinetics ; reaction mechanisms ; RNA ; Hydrolysis ; Kinetics ; Reaction mechanisms ; RNA ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The various mechanisms by which RNA is hydrolyzed are currently under intense investigation. The first step in the hydrolysis pathway is a cleavage-transesterification in which a 2′-OH group attacks a 3′,5′-phosphodiester linkage with departure of the 5′ group. The second step involves the opening of a 2′,3′-cyclic phosphodiester. Complications in these steps arise from multiple possible pathways involving specific acid and base as well as general acid and base catalysis. In addition, controversy exists concerning the protonation states of the phosphodiesters and any intermediate phosphoranes under various experimental conditions. A summary of mechanistic studies involving general and specific acid/base catalysis of RNA hydrolysis and the hydrolysis of RNA analogs is presented herein, along with the interpretations given by the original authors. Included are theoretical calculations, kinetic studies, pKa determinations, isotope effects, Hammett and Brønsted correlations, and model studies. Recent analyses of the mechanism of RNase A are also briefly reviewed. Two limiting mechanisms for the cleavage-transesterification step that unify the data in the literature and differ only in the role of the phosphorane and its protonation state are given at the outset. An analysis of the literature studies supporting these mechanisms is then provided.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199704321
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  • 9
    Electronic Resource
    Electronic Resource
    Understanding Reactivity Patterns of Radical CationsAbreviations used for one-electron oxidants: NR3·+: triarylaminium salt; CAN: Ce(NH4)2(NO3)6; Th·+: thianthrenium perchlorate; DCB: 1,4-dicyanobenzene; 1-CN: 1-cyanonaphthalene; TCB: 1,2,4,5-tetracyanobenzene; DCN: 1,4-dicyanonaphthalene; DCA: 9,10-dicyanoanthracene; TPP+: 2,4,6-triphenylpyrylium salt; CA: chloranil.Dedicated to Professor Waldemar Adam on the occasion of his 60th birthday (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 36 (1997), S. 2550-2589 
    Details
    ISSN: 0570-0833
    Keywords: electron transfer ; kinetics ; radical ions ; reaction mechanisms ; thermodynamics ; Electron transfer ; Kinetics ; Radicals ; Reaction mechanisms ; Thermodynamics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Over the last 15 years electron transfer activation has emerged as a valuable concept for accomplishing novel reactions and has found widespread application in the selective transformation of increasingly complex molecules. This review presents in a conceptualized manner the vast number of radical cation reactions obtained after chemical, electrochemical, and photoinduced one-electron oxidation. To familiarize the reader with the concepts of electron transfer a simple and straightforward classification of radical cation reactions has been devised to allow the presentation of a manifold of reactions in a readily understandable manner. Whenever possible, thermochemical and kinetic data are provided.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199725501
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  • 10
    Electronic Resource
    Electronic Resource
    Protonation of Unsaturated Hydrocarbon Ligands: Regioselectivity, Stereoselectivity, and Product Specificity (1996)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 35 (1996), S. 946-967 
    Details
    ISSN: 0570-0833
    Keywords: complexes with carbon ligands ; hydrocarbons ; protonation ; reaction mechanisms ; Carbon ligands ; Hydrocarbons ; Proton transfer ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Understanding the mechanisms of protonation of hydrocarbon ligands is fundamental to a wide range of chemistry including organic synthesis, organometallic chemistry, and even bioinorganic chemistry. Protonation at carbon or metal sites is often slow, with the result that in species containing both types of sites, initial protonation can be at either the metal or the carbon. This has fundamental consequences on the reactivity of hydrocarbon ligands, which are highlighted in this article. In particular, many reactions are apparently the result of a regioselective protonation on the basis of structural analysis of the isolated products. In fact, these products are often formed by an indirect route involving kinetically controlled protonation at the “wrong” site followed by rearrangement to form the thermodynamically controlled, apparently regioselective, product. Other aspects of the protonation mechanisms of complexes containing hydrocarbon ligands are discussed, with an emphasis on the manner in which competitive protonation at metal or ligand can be exploited to select which hydrocarbon is produced and to control the stereochemistry of the hydrocarbon.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199609461
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  • 11
    Electronic Resource
    Electronic Resource
    Ligand-Induced Directionality Shift in the Fe+-Mediated Dehydrogenation of 1,8-Diphenyloctane (1995)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 128 (1995), S. 649-650 
    Details
    ISSN: 0009-2940
    Keywords: C-H bond activation ; Ligand effects ; Iron chemistry ; Reaction mechanisms ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The presence of a cyclopentadienyl ligand brings about a complete shift of regioselectivity in the Fe+-mediated dehydrogenation of 1,8-diphenyloctane (1). While “bare” Fe+, due to the formation of an intramolecular sandwich-like complex, activates the internal C-4/C-5 positions of the alkyl chain, this chelate effect is no longer operative in the gas-phase chemistry of Fe(C5H5)+ with 1. Labeling experiments demonstrate that the C-1/C-2 and (to a minor extent) the C-2/C-3 methylene groups are activated, and a possible origin of this remarkable ligand effect is discussed.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19951280620
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  • 12
    Electronic Resource
    Electronic Resource
    The Course of the Willgerodt-Kindler Reaction of Alkyl Aryl KetonesA review article (a continuation of [1]) is being prepared in which the new compounds discussed in the present paper are treated in greater detail. A paper recently published [2] prompted us to make our concept of the course of the Willgerodt-Kindler reaction known.Respectfully dedicated to Prof. Dr. Karl Ziegler on the occasion of his 65th birthday (1964)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 19-28 
    Details
    ISSN: 0570-0833
    Keywords: Willgerodt-Kindler reaction ; Ketones ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ketones react with sulfur and NH3 or amines at room temperature to produce Δ3-thiazolines, 5-alkylidene-Δ3-thiazolines, Δ3-imidazoline-5-thiones, hexathiacycloheptane derivatives, α,α′-dioxodisulfides, bis-(1-aralk-1-yl) disulfides, or thiocarboxamides, depending on the coreactant and on the reaction conditions. It was recognized that the formation of all of these numerous types of compounds can be explained basically by primary thiolations and geminal dithiolations, which in conjunction with their reverse reaction (desulfurization) and the assumption of a thioreductone equilibrium permit a new interpretation of the course of the Willgerodt-Kindler reaction of alkyl aryl ketones.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196400191
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  • 13
    Electronic Resource
    Electronic Resource
    The Mechanism of the Action of Organometallic CatalystsDedicated to Prof. Dr. Karl Winnacker on the occasion of his 60th birthday. (1964)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 93-101 
    Details
    ISSN: 0570-0833
    Keywords: Organometallic catalysts ; Catalysis ; Reaction mechanisms ; Lithium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kinetic investigations of the polyreaction of isoprene with organolithium compounds as initiators in n-heptane as solvent indicate the following sequence of reactions: 1. formation of an adduct between a monomeric form of the organolithium compound and the isoprene and 2. reaction of this adduct with an associated form of the organolithium compound with insertion of the isoprene. The adduct formation is considered to be due to chemisorption, and proof of such chemisorption of a monomer (ethylene) is also demonstrated for a homogeneous Ziegler-type catalyst. All the reactions can be formulated in the form of cyclic structures with electron-deficient character. Postulation of such ring structures explains the surprising values obtained for the frequency factors and equilibrium constants.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196400931
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  • 14
    Electronic Resource
    Electronic Resource
    Phenol Oxidation ReactionsDedicated to Professor Dr. Hans Brockmann on the occasion of his 60th birthday (1963)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 723-735 
    Details
    ISSN: 0570-0833
    Keywords: Phenol oxidation ; C-C coupling ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of well-known phenol oxidation reactions for the preparation of compounds arising from C—C and C—O coupling has recently received increased attention. A selection from the large number of products obtainable by oxidation of mono- and polyhydric phenols and a discussion of the reaction mechanisms indicate the scope of this method. The formation of hydroxyphenylquinones and orceine dyes from resorcinol derivatives is explained. The synthesis of natural products by way of phenol oxidations is briefly discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196307231
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  • 15
    Electronic Resource
    Electronic Resource
    Kinetics and Mechanism of 1,3-Dipolr CycloadditionsExtended version of a lecture given at the Annual Meeting of the Dechema in Frankfurt/Main on June 14th, 1962, and of the Max Tishler Lecture at Harvard University on December 10th, 1962. (1963)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 633-645 
    Details
    ISSN: 0570-0833
    Keywords: Kinetics ; Dipolar cycloaddition ; Cycloaddition ; Heterocycles ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Criteria for the mechanism of 1,3-dipolar cycloadditions which lead to 5-membered rings are provided by the stereoselectivity observed with cis-trans isomeric dipolarophiles, by the effect of solvent and substituents on the rate constants, by the activation parameters, and by orientation phenomena. A concerted addition, which can also be described in terms of molecular orbitals and in which the two new σ-bonds are formed simultaneously, although not necessarily at equal rates, offers the best explanation of the experimental facts.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196306331
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  • 16
    Electronic Resource
    Electronic Resource
    The Mechanism of Bimolecular β-Elimination ReactionsBased on lectures presented in February-July, 1961, at University College, London, University College, Dublin, the University of Bologna and the University of Munich. (1962)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 1 (1962), S. 225-235 
    Details
    ISSN: 0570-0833
    Keywords: Elimination ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In bimolecular β-elimination (E 2 mechanism), several bonds are ruptured or formed in one concerted reaction step. However, the various aspects of bond-making or -breaking need not be completely synchronous. In the E 2 transition state for elimination HX, rupture of the C—X bond may be more advanced than that of the C—H linkage, or vice versa. Factors influencing the relative extents of rupture of these two bonds at the transition state are discussed, and the consequences of non-synchroneity in one sense or the other are developed from theory and illustrated from experiment. This treatment provides an understanding of the Hofmann-vs.-Saytzeff orientation problem.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196202251
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  • 17
    Electronic Resource
    Electronic Resource
    Electrophilic Substitutions at Saturated Carbon Atoms (1962)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 1 (1962), S. 382-393 
    Details
    ISSN: 0570-0833
    Keywords: Electrophilic reactions ; Reaction mechanisms ; Substitution ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The results obtained in recent years from investigations into the mechanisms of electrophilic substitution reaction at sp3-hybridized carbon atoms are reviewed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196203821
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