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  • Electronic Resource  (70)
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  • Reaction mechanisms
  • 1
    Electronic Resource
    Electronic Resource
    Effect of Solvation on Ozonolysis Reaction Intermediates and Transition States (2000)
    Springer
    Journal of molecular modeling 6 (2000), S. 608-617 
    Details
    ISSN: 0948-5023
    Keywords: Ozonolysis ; Ozone ; Reaction mechanisms ; Solvent effects ; Theoretical calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Electrostatic solvent effects on the ozonolysis of ethylene have been investigated using correlated ab initio and density functional approaches. We use a simple polarizable continuum model for the solvent. It allows us to evaluate the medium effect on both the electronic and nuclear structure of the chemical species involved in the reaction. The computations confirm that basically the reaction proceeds through the Criegee mechanism. However, formation of the van der Waals complexes ethyl-ene/ozone and carbonyl oxide/formaldehyde also appears to play a role. All the calculated species are stabilized with respect to the reactants except the transition state corresponding to the primary ozonide formation. In general, electrostatic solvent effects are relatively small for activation barriers of single reaction steps and more substantial for the corresponding reaction energies. Moreover, the medium significantly modifies the structure of some species for which polarization effects are crucial.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s0089400060608
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  • 2
    Electronic Resource
    Electronic Resource
    Mechanisms of Cyclopalladation Reactions in Acetic Acid: Not So Simple One-Pot Processes (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 217-224 
    Details
    ISSN: 1434-1948
    Keywords: Reaction mechanisms ; Cyclopalladation ; Acetic acid ; Pd-C bond stability ; Polynuclear species ; Palladium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The processes operating during the synthetic cyclopalladation reactions of imines in acetic acid have been studied from a kinetico-mechanistic point of view. These reactions include a fast initial coordination to the palladium through the N-donor atom of the imine, followed by the proper C-H bond activation to produce the acetato bridged dimeric species. At this point, the lability of the bridging acetato groups, the hydrolysis of the C-Pd bonds, and/or the hydrolysis of C=N exo bonds contribute to the generation of dark red polynuclear compounds. The processes occurring after the C-H activation have been followed kinetically, both from palladium acetate plus imine, and the synthetically pure isolated acetato dimers as starting materials. The kinetic and activation parameters have been found identical within experimental error whatever the starting material was (k323 = 1.5 × 10-4 s-1; ΔH# = 51 kJ mol-1; ΔS# = -163 JK-1 mol-1 ΔV# = +19 cm3 mol-1 for the 4-ClC6H4-CH=N-CH2-C6H5 imine derivative 1a). Acidolysis of C-Pd bonds has been found to occur in these polynuclear species. When alternative monomeric Cbenzylic-Pd bond-containing complexes are possible follow ups of the reactions produce them as final dead-end complexes (k323 = 2.2 × 10-5 s-1; ΔH# = 61 kJ mol-1; ΔS# = JK-1 mol-1 ΔV# ≈ 0 cm3 cm-1 for the [2,4,6-(CH3)3]C6H2-CH=N-CH2-[2-(CH3]C6[H4] imine derivative 3d). The same study has been carried out with primary amines in order to check the validity of the data if C=N bond hydrolysis is taking place in the imine derivatives with exo C=N bonds. For complexes with similar type of metallacycles, the results agree reasonably well with the proposed mechanism [k323 = 1.2·10-4 s-1, ΔH# = 46 kJ·mol-1, ΔS# = -180 J·K-1mol-1, ΔV# = -16 cm3·mol-1 for the polynuclear formation of the C6H5-CH2-NH2 derivative 4e; k323 = 3.0·10-4 s-1, ΔH# = 55 kJ·mol-1, ΔS
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New Insights into the Mechanism of Hydroperoxide Activation by Investigation of Dynamic Processes in the Coordination Sphere of Seven-Coordinated Molybdenum Peroxo Complexes (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 1107-1114 
    Details
    ISSN: 1434-1948
    Keywords: Catalysis ; Densitiy functional theory ; Epoxidation ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Seven-coordinated molybdenum oxobisperoxo complexes with chelate nitrogen donors like pyrazolylpyridines are catalysts for the epoxidation of olefins. An NMR spectroscopic and quantumchemical study on the fluxionality of the chelate ligand proves that during this process partial ligand dissociation takes place. This gave rise to a detailed theoretical study on the activation of CH3OOH at the model complex (NH3)2MoO(O2)2 including dissociation of one of the ammonia ligands and proton transfer from the hydroperoxide to one of the peroxo ligands.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99429_s.pdf or from the author.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    A Theoretical Study of the Properties and Reactivities of Ketene, Thioketene, and Selenoketene (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1411-1421 
    Details
    ISSN: 1434-193X
    Keywords: Ab initio calculations ; Reaction mechanisms ; Ketenes ; Cumulenes ; Cycloaddition reactions ; Nucleophilic additions ; Electrophilic addition ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The properties and reactivities of ketene, thioketene, and selenoketene were studied using the G2(MP2) level of theory. Calculated structures, vibrational frequencies, dipole moments, NMR chemical shifts, and charge distributions strongly suggest that thioketene and selenoketene are best represented by the neutral cumulenic form. Four prototype reactions were examined: ketene-ynol rearrangement, electrophilic and nucleophilic addition, and [2+2] cycloaddition. Thioketene and selenoketene were found to be more reactive than ketene in all reactions. In terms of chemistry, thioketene resembles selenoketene more than ketene. The variation of reactivity can readily be explained in terms of strain energy, electronegativity, and molecular orbital arguments.
    Additional Material: 5 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Hydrolytic Reactions of the cis-Methyl Ester of 3′-Deoxy-3′-thiothymidine 3′,5′-Cyclic(phosphorothiolate) (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1987-1991 
    Details
    ISSN: 1434-193X
    Keywords: Nucleotides ; Thiophosphates ; Hydrolyses ; Reaction mechanisms ; Kinetics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrolysis of the cis-methyl ester of 3′-deoxy-3′-thiothymidine 3′-S,5′-O-cyclic(phosphorothiolate) (1a) has been followed by HPLC and MS. At pH 〈 2 hydrolysis of the thiophosphate triester moiety is acid-catalyzed (first order), while between pH = 2 and 5 the reaction is pH-independent and at pH 〉 5 first order in hydroxide ion. The uncatalyzed and acid-catalyzed reactions yield two thiophosphate diesters, the 3′-S,5′-O-cyclic phosphorothiolate 2 and 3′-S-phosphorothiolate methyl ester 3, in a 9:1 and 1:3 molar ratio, respectively. The hydroxide ion catalyzed reaction gives the endocyclic P-O and P-S bond-cleavage products (3 and 4, respectively) in a 1:2 molar ratio. The pH-independent reaction is suggested to take place by attack of a water molecule on the carbon atom and concomitant C-O bond rupture, whereas the alkaline and acidic reactions involve attack of the nucleophile on the phosphorus atom and formation of a pseudorotating thiophosphorane intermediate. Under acidic conditions, cleavage of the N-glycosidic linkage competes with the phosphoester hydrolysis, corresponding to 20% of the hydrolysis products at pH 〈 1.
    Additional Material: 2 Tab.
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  • 6
    Electronic Resource
    Electronic Resource
    Products, Rates, and Mechanism of the Gas-Phase Condensation of Phenoxy Radicals between 500-840 K (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 921-928 
    Details
    ISSN: 1434-193X
    Keywords: Gas-phase chemistry ; Phenoxy radicals ; Dioxins ; Phenoxyphenols ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Phenols are demonstrated precursors of “dioxins” - polychlorinated dibenzo-p-dioxins (DDs) and dibenzofurans (DFs) - in thermal processes, especially incineration. Heterogeneous catalysis, depending on conditions, can play an important role, but mere gas-phase combination of phenolic entities to ultimately DD and/or DF is always possible. The present paper addresses the fundamental role of phenol itself. Phenol has long been known to give DF upon pyrolysis and in similar thermal reactions. In the liquid phase under oxidative conditions it yields five condensation products (A-E); this clearly occurs through the dimerization of two phenoxy (PhO) radicals, followed by enolisation/rearomatisation. Our study shows that in the gas phase, at the lower T end, such dimers are also formed, but still with very little DF. That DF, indeed, is almost the only condensation product at elevated temperatures is substantiated by thermochemical-kinetic analysis (favouring the pathway of ortho-C/ortho-C combination of two PhO radicals), as well as by results obtained with two plausible intermediates, viz. 2,2′-dihydroxybiphenyl (A) and 2-phenoxyphenol (C). Mechanisms for the requisite enolisation and dehydration steps leading to DF are discussed.
    Additional Material: 3 Ill.
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  • 7
    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.
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  • 8
    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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  • 9
    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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  • 10
    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.
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  • 11
    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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  • 12
    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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  • 13
    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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  • 14
    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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  • 15
    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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  • 16
    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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  • 17
    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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  • 18
    Electronic Resource
    Electronic Resource
    Fe(I)-Mediated Regio- and Stereoselective C—C/C—H Bond Activation of Internal Methylene Groups of α,ω-Diphenylalkanes (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 261-265 
    Details
    ISSN: 0009-2940
    Keywords: Bond activation ; C—H ; C—C ; Iron chemistry ; Reaction mechanisms ; Chelate effects ; Tandem mass spectrometry ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For three α,ω-diphenylalkanes the mechanistic details of the Fe+-mediated activation of C—H and C—C bonds in the gas phase have been elucidated by isotopic labelling experiments. The unimolecular reactions, i.e. dehydrogenation of the alkane chain, formation of ethylene from internal methylene groups, and generation of toluene, proceed largely with high selectivity. Particularly interesting are the results for the dehydrogenation of the Fe+ complex 3-Fe+ of 1,8-diphenyloctane which involves to 93% the internal methylene groups C-4/C-5. In addition, the study of the stereoisotopomers 3c-d provides evidence for the operation of isotopically sensitive branching (“metabolic switching”) in the reaction, and the analysis of the data suggests that the selectivity of the reaction is, most likely, due to a sandwich-type structure.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941270136
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  • 19
    Electronic Resource
    Electronic Resource
    Scales of Nucleophilicity and Electrophilicity: A System for Ordering Polar Organic and Organometallic Reactions (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 33 (1994), S. 938-957 
    Details
    ISSN: 0570-0833
    Keywords: Reaction mechanisms ; Nucleophilicity ; Electrophilicity ; Carbocations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Contrary to widely held opinion, for many reactions in organic and organometallic chemistry it is possible to define nucleophilicity and electrophilicity parameters that are independent of the reaction partners. This phenomenon, discovered by Ritchie during the early 1970s for reactions of highly stabilized carbenium and diazonium ions with n-nucleophiles, also occurs with reactions of carbenium ions with aliphatic and aromatic π-electron systems and in hydride transfer reactions. With the aid of the scales of nucleophilicity and electrophilicity set out here, which extend over eighteen orders of magnitude, forecasts can be made about the feasibility and rate of a given CC bond formation, ionic reduction, or diazo coupling. Linkage with the reactivity scales of Ritchie and Sweigart/Kane-Maguire enables a unified treatment of a large number of polar reactions.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199409381
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    Organizing Principle of Complex Reactions and Theory of Coarctate Transition States (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 33 (1994), S. 255-276 
    Details
    ISSN: 0570-0833
    Keywords: Rearrangement ; Coarctate transition states ; Reaction mechanisms ; Concerted reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The majority of concerted reactions proceeds by a simultaneous breaking and making of only one bond at each atom involved in the reaction. If this process follows an alternating cyclic sequence, the reactions are called pericyclic. However, there is a hitherto never consistently characterized class of reactions that proceeds by breaking and making two bonds at one or more atoms at a time. The striking relationships that are purely descriptive and formal in the first instance are explained by a common physical principle. Theoretical insight not only permits predictions of mechanisms and stereochemistry; the qualitative theory is also used as an organizing principle for the known reactions and as a tool for predicting unprecedented reactions of this type.
    Additional Material: 23 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199402551
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  • 21
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    Time-Resolved Photoacoustic Calorimetry: From Carbenes to Proteins (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 33 (1994), S. 294-302 
    Details
    ISSN: 0570-0833
    Keywords: Calorimetry ; Photoacoustic calorimetry ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Why have molecules only been seen but not heard? For over a century chemists have probed reactions with various spectroscopic methods to learn about structures, dynamics, and reactivities of their molecules. What they have not done is to listen to their molecules react. Although the photoacoustic phenomenon has been known since 1880, it is only in the last twenty years that technology has developed to the point where sound waves produced by reacting molecules can be time resolved and the information contained within the waves deciphered. The information content within the photoacoustic wave is indeed rich, for one can learn about the dynamics and the magnitude of enthalpy changes associated with the reaction as well as the changes in molecular volume. This review article chronicles the development of time-resolved photoacoustic calorimetry and its application to a variety of reactions encountered in organic and organometallic chemistry and biochemistry.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199402941
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  • 22
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    Kinetics and mechanism of the degradation of la-acetylmitomycin C in aqueous solution (1993)
    Springer
    Pharmacy world & science 15 (1993), S. 123-127 
    Details
    ISSN: 1573-739X
    Keywords: Catalysis ; Drug stability ; Mitomycins ; Reaction kinetics ; Reaction mechanisms ; Stereoisomers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The acid-catalyzed degradation of mitomycin C is supposed to be governed, to a certain extent, by the protonation status of the aziridine nitrogen in the molecule as well as the protonation degree of the opened aziridine function in a key intermediate species, formed during mitomycin degradation. In order to obtain information about the contribution of the protonation degrees of these functions in controlling the degradation processes, we investigated the degradation of 1a-acetylmitomycin C in acidic aqueous solutions. In the presence of 0.001 mol/l phosphate buffers five 1-hydroxy and mono-acetyl mitosenes are formed, whereas in 1.0 mol/l acetate buffers a total of eight products could be identified, two of them being diacetyl mitosenes. Over the whole pH range studied the formation of 1,2-Z-mitosenes prevails, indicating that, contrary tomitomycin C, a pH-independent factor controls the ultimate 1,2-stereochemistry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02113940
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  • 23
    Electronic Resource
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    Optimization in organic synthesis. An approach to obtaining kinetic information by sequential response surface modelling. Outline of the principles (1993)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 7 (1993), S. 341-367 
    Details
    ISSN: 0886-9383
    Keywords: Reaction kinetics ; Initial rate ; Kinetic order ; Response surface modelling ; Canonical analysis ; Organic synthesis ; Optimization ; Reaction mechanisms ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is presented by which it is possible to estimate the initial rate of chemical reactions when the experimental conditions are varied according to a response surface design. The method is intended as a complementary method for analysing data obtained from experiments in synthetic chemistry when the objective is to optimize the yield of the reaction.Data obtained by simulations have been used to develop the method. From the simulated reactions it is shown that sequential analysis of the chemical yield of the reaction makes it possible to estimate models which describe how the parameters of the response surface of the yield vary over time. The derivatives of these time functions of the response surface parameters can be used to define a rate function which describes how the variations in the experimental conditions influence the rate of the reaction.It is shown how such rate functions can be used to afford reasonable estimates of the initial rates of the reaction. The initial reaction rates thus estimated can be used to determine the kinetic order of the reactants and also to provide estimates of the activation energy of the reaction.A thorough discussion of how canonical analysis of the rate function may assist in the elucidation of reaction mechanisms is given.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180070503
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    Electron Transfer Reactions in Chemistry: Theory and Experiment (Nobel Lecture)Copyright © The Nobel Foundation 1993. - We thank the Nobel Foundation, Stockholm, for permission to print this lecture. (1993)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 32 (1993), S. 1111-1121 
    Details
    ISSN: 0570-0833
    Keywords: Electron transfer ; Reaction mechanisms ; Nobel lecture ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Since the late 1940s, the field of electron transfer processes has grown enormously, both in chemistry and biology. The development of the field, experimentally and theoretically, as well as its relation to the study of other kinds of chemical reactions, presents to us an intriguing history, one in which many threads have been brought together. In this lecture, some history, recent trends, and my own involvement in this research are described.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199311113
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  • 25
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    Computer-Assisted Solution of Chemical Problems - The Historical Development and the Present State of the Art of a New Discipline of ChemistryDedicated to Professor Karl-Heinz Büchel (1993)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 32 (1993), S. 201-227 
    Details
    ISSN: 0570-0833
    Keywords: Computer chemistry ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The topic of this article is the development and the present state of the art of computer chemistry, the computer-assisted solution of chemical problems. Initially the problems in computer chemistry were confined to structure elucidation on the basis of spectroscopic data, then programs for synthesis design based on libraries of reaction data for relatively narrow classes of target compounds were developed, and now computer programs for the solution of a great variety of chemical problems are available or are under development. Previously it was an achievement when any solution of a chemical problem could be generated by computer assistance. Today, the main task is the efficient, transparent, and non-arbitrary selection of meaningful results from the immense set of potential solutions - that also may contain innovative proposals. Chemistry has two aspects, constitutional chemistry and stereochemistry, which are interrelated, but still require different approaches. As a result, about twenty years ago, an algebraic model of the logical structure of chemistry was presented that consisted of two parts: the constitution-oriented algebra of be- and r-matrices, and the theory of the stereochemistry of the chemical identity group. New chemical definitions, concepts, and perspectives are characteristic of this logic-oriented model, as well as the direct mathematical representation of chemical processes. This model enables the implementation of formal reaction generators that can produce conceivable solutions to chemical problems - including unprecedented solutions - without detailed empirical chemical information. New formal selection procedures for computer-generated chemical information are also possible through the above model. It is expedient to combine these with interactive methods of selection. In this review, the Munich project is presented and discussed in detail. It encompasses the further development and implementation of the mathematical model of the logical structure of chemistry as well as the experimental verification of the computer-generated results. The article concludes with a review of new reactions, reagents, and reaction mechanisms that have been found with the PC-programs IGOR and RAIN.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199302011
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  • 26
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    Pulse radiolysis of aromatic amino acids — State of the art (1992)
    Springer
    Amino acids 2 (1992), S. 195-214 
    Details
    ISSN: 1438-2199
    Keywords: Amino acids ; Pulse radiolysis ; Aromatic amino acids ; Reaction mechanisms ; Free radicals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The pulse radiolysis method as well as the primary processes of water radiolysis and the spectroscopic characteristics of H, OH, HO2/O2 − and e aq - are briefly presented. Subsequently, kinetic and spectroscopic data of the transients resulting from the resolved multi site attack on aromatic amino acids are discussed. The reactivity of H and e aq - with the same substrates, as well as the effect of oxygen on the major radiolytic processes are reviewed. Finally, the formation of tryptophan radical cation is mentioned shortly. The presented radiation mechanisms are the fundamentals for radiolytic processes occurring in proteins, enzymes and hormones in the living cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00805942
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  • 27
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    Enantioselective Addition of Organometallic Reagents to Carbonyl Compounds: Chirality Transfer, Multiplication, and AmplificationParts of this review were presented by R. N. during his Merck-Schuchardt lecture series in the Federal Republic of Germany in May 1989. Ar represents aryl substituents in this article. (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 30 (1991), S. 49-69 
    Details
    ISSN: 0570-0833
    Keywords: Chirality transfer ; Carbonyl compounds ; Addition ; Enantioselectivity ; Synthetic methods ; Alcohols ; Reaction mechanisms ; Catalysis ; Alkylation ; Organometallic compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nucleophilic addition of organometallic reagents to carbonyl substrates constitutes one of the most fundamental operations in organic synthesis. Modification of the organometallic compounds by chiral, nonracemic auxiliaries offers a general opportunity to create optically active alcohols, and the catalytic version in particular provides maximum synthetic efficiency. The use of organozinc chemistry, unlike conventional organolithium or -magnesium chemistry, has realized an ideal catalytic enantioselective alkylation of aldehydes leading to a diverse array of secondary alcohols of high optical purity. A combination of dialkylzinc compounds and certain sterically constrained β-dialkylamino alcohols, such as (-)-3-exo-dimethylaminoiso- borneol [(-)-DAIB], as chiral inducers affords the best result (up to 99% ee). The alkyl transfer reaction occurs via a dinuclear Zn complex containing a chiral amino alkoxide, an aldehyde ligand, and three alkyl groups. The chiral multiplication method exhibits enormous chiral amplification: a high level of enantioselection (up to 98%) is attainable by use of DAIB in 14% ee. This unusual nonlinear effect is a result of a marked difference in chemical properties of the diastereomeric (homochiral and heterochiral) dinuclear complexes formed from the dialkylzinc and the DAIB auxiliary. This phenomenon may be the beginning of a new generation of enantioselective organic reactions.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199100491
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    The Elucidation of Peroxyl Radical Reactions in Aqueous Solution with the Help of Radiation-Chemical MethodsDedicated to Professor Kurt Schaffner on the occasion of his 60th birthday (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 30 (1991), S. 1229-1253 
    Details
    ISSN: 0570-0833
    Keywords: Reaction mechanisms ; Free radicals ; Peroxyl radicals ; Radical reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Whenever free radicals are formed, independent of whether this occurs thermally, is induced by UV or ionizing irradiation, or takes place in redox reactions, they are converted rapidly into the corresponding peroxyl radicals in the presence of oxygen. Peroxyl radical reactions in aqueous environments are observed not only in aquatic systems (e.g., rivers, lakes and oceans) but also in the living cell and to a considerable degree even in the atmosphere (in water droplets). The peroxyl radical chemistry occurring in this medium is often very different from that observed in the gas phase or in organic solvents. In spite of the great importance of these reactions in medicine (for example in anti-cancer irradiation therapy and ischaemia) there have been comparatively few studies of peroxyl reactions in aqueous media. Radiation-chemical techniques such as pulse radiolysis offer the best means for carrying out such studies, so that it is not surprising that the majority of the information available in this area has been obtained with the help of radiation-chemical methods. The radiation chemistry of water can be con trolled in such a manner that the main products are ·OH radicals (90 % yield), which react with substrate molecules to give substrate radicals and in the presence of oxygen to give substrate peroxyl radicals. The experimental conditions can also be varied in such a way that HO2·/O2·⊖ radicals can be formed in 100 % yield and caused to react with substrates. We therefore have a simple access to these intermediates, which are extremely important in biological systems. A detailed product analysis, supported by kinetic studies carried out with the help of pulse radiolysis, has been used to clarify the chemistry of a series of peroxyl radicals, so that sufficient material is now available to justify a review of the variety of the peroxyl radical reactions studied by means of radiation-chemical methods. A more general survey of the physical properties of the peroxyl radicals and their unimolecular and bimolecular reactions will be followed by a discussion of selected examples of various classes of substance. Because of the great biological importance of radical-induced DNA damage this area will also be treated briefly.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199112291
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    Spectroscopy of Fluid Phases - The Study of Chemical Reactions and Equilibria up to High Pressures (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 30 (1991), S. 641-653 
    Details
    ISSN: 0570-0833
    Keywords: Reaction mechanisms ; Spectroscopy ; Equilibria ; High-pressure chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The properties of fluid phases can be altered considerably by the external conditions. Phase equilibria and chemical equilibria can be greatly affected, and it is possible to carry out chemical reactions by exploiting the special properties of compressed fluid phases. The use of high pressure in chemical reactions is of considerable diagnostic and preparative value. Applied research is directed towards elucidating the details of existing technical high pressure processes and to the development of novel fluid phase reactions where the application of high pressure is able to induce selectivity. In order to pursue these lines of research, and to study structure and dynamics throughout the entire range from gaseous to liquidlike states, it is important to have spectroscopic methods for characterizing systems at high pressures and temperatures. This article is concerned with quantitative absorption spectroscopy in the infrared to the ultraviolet spectral region at pressures up to about 7 kbar and temperatures up to 900 K.
    Additional Material: 25 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199106411
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    The Isoinversion Principle - a General Model of Chemical SelectivityDedicated to Vladimir Prelog and to the memory of Horst Pracejus (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 30 (1991), S. 477-515 
    Details
    ISSN: 0570-0833
    Keywords: Selectivity ; Isoinversion principle ; Reaction mechanisms ; Stereoselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A large number of successful methods for chirality transfer, using either stoichiometric or catalytic chiral auxiliaries, are in use today. However, there is a lack of practical and dynamic selectivity models, i.e. models which take into account the entire reaction sequence, and which allow simple and reliable assessment, optimization and prediction of selectivity in asymmetric syntheses. The models that are available are either too strongly biased to the steric requirement of the particular molecules reacting, but do not go beyond classical considerations of static facial differentiation, or they take a demanding, theoretical approach, which because of its inherent limitations and the great theoretical effort required has not yet found its way into the practical world of the synthetic chemist. The “Isoinversion Principle”, developed on the basis of Eyring's theory, closes this gap. With its aid, the synthetic chemist can determine the characteristic isoinversion temperature Ti for the reaction type of interest from a few temperature-dependent measurements of selectivity parameters. Ti then affords information on interesting questions such as optimization etc. The advantage of this method is that it is useful not only for stereoselectivity, but for any kind of process where selectivity in general (regio-,chemo-, etc) is generated at two or more stages of a reaction sequence, regardless of whether these reactions involve the ground state or a diabatic photoprocess. The present review will demonstrate that this generation of selectivity at two or more stages of a reaction sequence occurs more commonly than is generally thought.
    Additional Material: 52 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199104771
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    On the Conformation and Structure of Organometal Complexes in the Solid State: Two Studies Relevant to Chemical SynthesisDedicated to Professor Jack Dunitz (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 29 (1990), S. 256-272 
    Details
    ISSN: 0570-0833
    Keywords: Solid-state reactions ; Complexes ; Organometallic compounds ; Conformation analysis ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformational preferences of two classes of organometal complexes have been surveyed by inspecting the Cambridge Structural Database (CSD). Lewis acid carbonyl complexes demonstrate a variety of coordination geometries, depending on the electronic and steric requirements of the carbonyl ligands and the nature of the Lewis acid. Similarly, the solid-state conformation of various π-bonding ligands in metal acyl, metal nitrosyl, metal acetylene, and metal imido complexes is revealed. These insights have stimulated the development of a conformational model that is based on considerations of π-bond hybridization and frontier molecular orbital theory. The analyses are relevant to the mechanism and transition structures of many synthetically important transformations. A deeper understanding of the conformational properties of organometal complexes, based on accurate structural information, will likely expedite the design and improvement of metal-mediated processes.
    Additional Material: 49 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199002561
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    CC Bond Formation by Addition of Carbenium Ions to Alkenes: Kinetics and MechanismDedicated to Professor Rolf Huisgen on the occasion of his 70th birthday (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 29 (1990), S. 1371-1384 
    Details
    ISSN: 0570-0833
    Keywords: Kinetics ; Addition ; Alkenes ; Reaction mechanisms ; Carbocations ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The addition of carbenium ions to CC double bonds, a key step in many syntheses in organic and macromolecular chemistry, is analyzed using the Lewis acid promoted reactions of alkyl chlorides with alkenes as an example. Stereochemical and kinetic experiments suggest that the transition state is slightly bridged and product-like. Rearrangements of the carbenium ions that result from the electrophilic attack can be minimized by adding salts with nucleophilic counter ions. The thermodynamics of the addition reactions are analyzed, and the conditions necessary in order to observe the back reaction (i.e. the Grob fragmentation) are discussed. Multiparameter equations that predict rate constants are derived from kinetic studies on the reactivities of carbenium ions and alkenes. Reactivity-selectivity relationships over a reactivity range that covers eight orders of magnitude show that the structure of the transition state is only changed by variation of substituents in the immediate vicinity of the reaction center.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199013713
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    Elementary Steps in Heterogeneous CatalysisFrom a paper presented at the awarding of the A-Mittasch Medal during a colloquium celebrating the 125th. anniversary of the founding of BASF on September 24, 1990 in Ludwigshafen (FRG). (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 29 (1990), S. 1219-1227 
    Details
    ISSN: 0570-0833
    Keywords: Heterogeneous catalysis ; Reaction mechanisms ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Despite the great importance of heterogeneous catalysis, research in this field has long been characterized by its empiricism. Now, however, thanks to the rapid development of methods in surface physics, the elementary steps can be identified at the atomic level and the underlying principles understood. Defined single crystal surfaces are employed as models, based on the analysis of the surfaces of ‘real’ catalysts. Direct images, with atomic resolution, can be obtained using scanning tunneling microscopy, while electron spectroscopic methods yield detailed information on the bonding state of adsorbed species and the influence of catalyst additives (promotors) upon them. The successful application of this approach is illustrated with reference to the elucidation of the mechanism of ammonia synthesis. The catalyst surface is usually transformed under reaction conditions, and, as the processes involved are far-removed from equilibrium, such transformations can lead to intrinsic spatial and temporal self-organization phenomena. In this case, the reaction rate may not remain constant under otherwise invariant conditions but will change periodically or exhibit chaotic behavior, with the formation of spatial patterns on the catalyst surface.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199012191
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    The Stereoselectivity of Intermolecular Free Radical Reactions [New Synthetic Methods (78)]Dedicated to Professor Christoph Rüchardt on the occasion of his 60th birthday (1989)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 969-980 
    Details
    ISSN: 0570-0833
    Keywords: Stereoselectivity ; Reaction mechanisms ; Synthetic methods ; Free radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The regio- and chemoselectivities of free radical reactions are often high and largely predictable; systematic studies have now shown that the stereoselectivity of free radical reactions can also be directed. Examples involving five- and six-membered cyclic radicals will be used to show how steric and stereoelectronic effects influence the diastereoselectivity of reactions of cyclic radicals with olefins. The temperature, the solvent, and the nature of the radical scavenger used also play a role, so that, if the correct reaction conditions are used, the stereoselectivity of reactions for cyclic reactants can be very high. Lower stereoselectivities are often observed for reactions between acyclic radicals and acyclic alkenes. However, preliminary experiments have indicated that under certain conditions such systems can also react in a stereoselective manner.
    Additional Material: 9 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198909693
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    Reaction Mechanisms in Heterogeneous Catalysis; C—H Activation as a Case Study (1989)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 135-145 
    Details
    ISSN: 0570-0833
    Keywords: Reaction mechanisms ; Heterogeneous catalysis ; C-H activation ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heterogeneous catalysis is changing from an empirical art to an exact science. The various methods for the analysis of solids and surfaces, constantly refined by materials science and surface science, seem to be almost unlimited. The increasing availability of atomic resolution microscopy as well as synchrotron radiation allows the characterization of catalyst particles, surface structures, surface processes and surface intermediates. We have learned to determine the surface structure sensitivity of catalytic reactions. Thermodynamic and kinetic data of catalytic reactions are now determined routinely. Isotopic exchange and labeling experiments provide information about reactant-catalyst interactions. How much have we learned through these techniques about the nature or mechanism of heterogeneously catalyzed reactions? The following article attempts to summarize the progress and the problems encountered in mechanistic studies of C—H bond formation and activation in a hydrogen atmosphere as an example for the present state of the understanding of reaction mechanisms in heterogeneous catalysis.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198901353
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    Reaction gas chromatography: Study of the photodecomposition of halogenated hydrocarbons (1988)
    Springer
    Chromatographia 25 (1988), S. 621-626 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Pre-column photolysis ; Halogenated hydrocarbons ; Identification of photolysis products ; Reaction mechanisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Photodecomposition of chloro- and bromoderivatives of saturated, unsaturated and aromatic hydrocarbons has been studied under flow conditions using reaction gas chromatography. The photodegradation products were separated on a column coated with squalane and identified by comparing the measured retention data with those of standards and published retention indices, The results can be used to clarify the decomposition of such compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02327659
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    Electron Transfer and Charge Transfer: Twin Themes in Unifying the Mechanisms of Organic and Organometallic Reactions (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 1227-1266 
    Details
    ISSN: 0570-0833
    Keywords: Electron transfer ; Charge transfer ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The broad varieties of organic and organometallic reactions merge into a common unifying mechanism by considering all nucleophiles and electrophiles as electron donors (D) and electron acceptors (A), respectively. Comparison of outer-sphere and inner-sphere electron transfers with the aid of Marcus theory provides the thermochemical basis for the generalized free energy relationship for electron transfer (FERET) in Equation (37) and its corollaries in Equations (43) and (44) that have wide predictive applicability to electrophilic aromatic substitutions, olefin additions, organometallic cleavages, etc. The FERET is based on the conversion of the weak nucleophile-electrophile interactions extant in the ubiquitous electron donor - acceptor (EDA) precursor complex [D, A] to the radical ion pair [D⊕, A⊖], for which the free energy change can be evaluated from the charge-transfer absorption spectra according to Mulliken theory. FERET analysis thus indicates that the charge-transfer ion pairs [D⊕, A⊖] are energetically equivalent to the transition states for nucleophile/electrophile transformations. The behavior of such ion pairs can be directly observed immediately following the irradiation of the charge-transfer bands of various EDA complexes with a 25-ps laser pulse. Such studies confirm the radical ion pair [Arene⊕, NO2] as a viable intermediate in electrophilic aromatic nitration, as presented in the electron-transfer mechanism between arenes and the nitryl cation (NO2⊕) electrophile.
    Additional Material: 38 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198812273
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    The topology of energy hypersurfaces IV. Generator sets for the fundamental group of reaction mechanisms and the complete set of reaction paths (1985)
    Springer
    Theoretical chemistry accounts 67 (1985), S. 91-113 
    Details
    ISSN: 1432-2234
    Keywords: Reaction mechanisms ; synthesis planning ; molecular design ; potential surfaces ; reaction path
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A countable set of distinguished fundamental reaction mechanisms on a potential surface serves as the set of generators for the fundamental group of reaction mechanisms. The effects of a change in the upper limit for energy on such groups are described with the aid of a lower semilattice, introduced into the family of all fundamental groups of reaction mechanisms, supported by the given potential energy surface. The algebraic structure of all reaction paths is described with the aid of groupoids and various subgroupoids and semigroups derived from them.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00547897
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    Chelation or Non-Chelation Control in Addition Reactions of Chiral α- and β- Alkoxy Carbonyl Compounds [New Synthetic Methods (44)] (1984)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 23 (1984), S. 556-569 
    Details
    ISSN: 0570-0833
    Keywords: Addition ; Alkoxy carbonyl compounds ; Synthetic methods ; Chelates ; Stereoselectivity ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The addition of C-nucleophiles such as Grignard reagents or enolates to chiral α- or β-alkoxy aldehydes or ketones creates a new center of chirality and is therefore diastereogenic. In order to control stereoselectivity, two strategies have been developed: (1) Use of Lewisacidic reagents which form intermediate chelates, these being attacked stereoselectively from the less hindered side (chelation control); (2) use of reagents incapable of chelation, stereoselective attack being governed by electronic and/or steric factors (non-chelation control). Generally, the two methods lead to the opposite sense of diastereoselectivity. It is possible to predict the outcome by careful choice of organometallic reagents containing elements such as Li, Mg, B, Si, Sn, Cu, Zn, or Ti.For corrigendum see DOI:10.1002/anie.198407461
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/anie.198405561
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    Which Factors Determine the Reactivity and Regioselectivity of Free Radical Substitution and Addition Reactions? (1982)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 21 (1982), S. 401-410 
    Details
    ISSN: 0570-0833
    Keywords: Regioselectivity ; Radical reactions ; Addition ; Radical reactions ; Reaction mechanisms ; Substitution ; Free radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relative importance of bond strength, steric effects, and polarity in determining the rate and orientation of free radical subsitution and free radical addition reaction is considered. The factors which control substitution reaction (radical transfer reaction) are gathered together as five “rules”, and a similar five “rules” are proposed for addition rections. These “rules” are shown to be special cases of two “laws” which govern all free radical reactions.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/anie.198204011
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    ETC: A Mechanistic Concept for Inorganic and Organic ChemistryETC: “Electron Transfer Catalysis”; DAISET: “Double Activation Induced by Single Electron Transfer”; SET: “Single Electron Transfer”.Dedicated to Professor Jacques Metzger on the occasion of his 60th birthday (1982)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 21 (1982), S. 1-23 
    Details
    ISSN: 0570-0833
    Keywords: Electron transfer catalysis ; Electrocatalysis ; Reaction mechanisms ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The concept of electron transfer catalysis (ETC), or more specifically “Double Activation Induced by Single Electron Transfer” (DAISET) gives an opportunity to connect experimental facts never previously correlated. The first activation results from the transfer of an electron to (or from) a molecular species; the second activation results from the build-up of a reaction chain able to reproduce the species formed in the first step. The starting point of this review is the SRN1 mechanism where principle and experimental diagnostic criteria are critically discussed. The thermal and photochemical exchange and substitution reactions of PtIV complexes are then reviewed together with the exchange reaction [AuCl4]-/Cl-, reactions with Grignard reagents and other organometallic reagents, as well as the redox behavior of electronically excited organic compounds. Photochemical applications, including solar energy conversion are discussed. New aspects are also presented for the mechanistic problem “SN2 reaction or SET process?” Moreover, the concept has significance for SH2 reactions at metal centers, molecule-induced homolyses, reactions of complexes, as well as electrochemical processes.-Unless otherwise specified, only double activation (DAISET) processes will be discussed in this article.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/anie.198200013
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    Oxygen Transfer from Inorganic and Organic Peroxides to Organic Substrates: A Common Mechanism? (1982)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 21 (1982), S. 734-750 
    Details
    ISSN: 0570-0833
    Keywords: Oxygen transfer ; Peroxides ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this progress report an attempt is made to rationalize, from a mechanistic point of view, the different ways in which oxygen is transferred from inorganic and organic peroxides to nucleophilic substrates, particularly olefins. Oxygen transfer from transition-metal peroxides, which is relevant to catalytic oxidations using O2, H2O2 or ROOH, occurs via a cyclic or “pseudocyclic” peroxymetalation in which a dioxametallacycle is formed. Owing to the wide discrepancy between peroxymetalation and the conventional oxidation mechanism, i.e. nucleophilic attack of the substrate at the electrophilic “active oxygen”, we propose an alternative mechanism involving dioxiranes as the reactive species. The generation of dioxiranes appears to be a common denominator in the reactions of most organic peroxides e.g. peroxy acids, the reaction of electrophilic ketones with H2O2, or ozonizations. Oxygen transfer from dioxirane reagents probably involves the formation of a charge-transfer π-complex between the substrate and the carbon atom of the dioxirane, and the subsequent formation of a cyclic peroxidic intermediate.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/anie.198207341
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    Critical level topology of energy hypersurfaces (1981)
    Springer
    Theoretical chemistry accounts 60 (1981), S. 97-110 
    Details
    ISSN: 1432-2234
    Keywords: Reaction topology ; Potential surfaces ; Reaction mechanisms ; Critical points
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Topologies are introduced into the nuclear configuration space R of molecular systems, based upon equipotential contour hypersurfaces on the otential energy hypersurface E. Critical level topologies T fc and T fc′, based upon the number and distribution of various critical points of E, are of particular importance, since they represent convenient yet rigorous mathematical models for relations between elementary reaction mechanisms, and for relations between open sets of nuclear geometries which are classically accessible at a given total energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00550329
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    Reaction Paths on Multidimensional Energy HypersurfacesBased on an inaugural lecture at ETH Zürich, June 14, 1979. (1980)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 19 (1980), S. 1-13 
    Details
    ISSN: 0570-0833
    Keywords: Reaction mechanisms ; Multidimensional energy hypersurfaces ; Energy hypersurfaces ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Theoretical investigation of a chemical reaction requires detailed knowledge of the potential energy of the molecular system. As a first step in such a study, minimum-energy reaction paths have to be mapped on a generally multidimensional molecular potential surface. Even at this stage problems are encountered that have only recently been solved satisfactorily. The difficulties involved and various ways to handle them are discussed in connection with a two-parametric model potential. Three chemical reactions examined illustrate the usefulness of such theoretical investigations as well as their current limitations.
    Additional Material: 23 Ill.
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    URL: http://dx.doi.org/10.1002/anie.198000013
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    Electrocyclic Ring Opening Reactions of Ethylene OxidesExtended version of the Roger Adams Award Address, National Organic Symposium of the American Chemical Society, Fort Collins (Col.), June 24, 1975, and a plenary lecture delivered at the GDCh General Meeting at Cologne, Sept. 9, 1975. (1977)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 16 (1977), S. 572-585 
    Details
    ISSN: 0570-0833
    Keywords: Electrocyclic reactions ; Ring opening ; Reaction mechanisms ; Carbonyl ylides ; Ylides ; Ethylene oxides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituents capable of stabilizing negative charge endow ethylene oxides with the ability to undergo electrocyclic ring opening at the CC bond; heating or irradiation generates small equilibrium concentrations of carbonyl ylides which can engage in 1,3-dipolar cycloadditions. Apart from the normal conrotatory mode of ring opening, predicted by the Woodward-Hoffmann rules, the disrotatory process, forbidden by orbital symmetry, also appears to occur in the case of α-cyano-cis-stilbene oxide. Kinetic studies on α-cyano-trans -and -cis-stilbene oxide permit construction of the energy profile for electrocyclic ring opening to give the stereoisomeric carbonyl ylides and for their recyclization and rotation.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/anie.197705721
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    Mechanistic Aspects of Olefin Metathesis (1976)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 15 (1976), S. 401-409 
    Details
    ISSN: 0570-0833
    Keywords: Metathesis ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper views regarding the nature of the transition state in olefin metathesis are discussed. Earlier concepts that assumed a pairwise scrambling mechanism have been recently challenged. Metathesis studies involving acyclic as well as cyclic olefins have been reported which strongly suggest a chain process that may involve a carbene-to-metallocycle interconversion as the pathway responsible for transalkylidenation. Catalytic systems that display a low apparent metathesis activity on terminal olefins display a unique specificity in cross reactions with internal olefins. Critical experiments indicate that terminal olefins rapidly undergo regenerative metathesis preferentially. Results suggest that in the transient metallocycle, the most stringent steric requirements occur at the β-carbon, although the origin of this steric demand is not obvious.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/anie.197604011
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    The Fischer-Tropsch Synthesis: Molecular Weight Distribution of Primary Products and Reaction Mechanism (1976)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 15 (1976), S. 136-141 
    Details
    ISSN: 0570-0833
    Keywords: Fischer-Tropsch synthesis ; Molecular weight distribution ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An evaluation of literature data concerning the production of hydrocarbons and alcohols by the Fischer-Tropsch procedure indicates that the molecular weight distribution of the primary products can be described by the Schulz-Flory equation (“normal” or “most probable” distribution). It follows that the highest attainable selectivity for a given molecular weight range can be calculated. A reaction mechanism is suggested.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/anie.197601361
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    Mechanism of Ozonolysis (1975)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 14 (1975), S. 745-752 
    Details
    ISSN: 0570-0833
    Keywords: Ozonolysis ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The formation of ozonides (1,2,4-trioxolanes) from alkenes and ozone can be described as a succession of three [2+3] cycloadditions or cycloreversions involving primary ozonides (1,2,3-trioxolanes) and aldehyde or ketone oxides as decisive intermediates, all of which have finite lifetimes. There is no warranted experimental basis for assuming an alternative mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.197507451
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    Stereochemistry of Reaction Paths as Determined from Crystal Structure Data - A Relationship between Structure and Energy (1975)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 14 (1975), S. 460-473 
    Details
    ISSN: 0570-0833
    Keywords: Stereochemistry ; Crystal structure ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The three-dimensional structure of frequently occurring molecular fragments has been studied systematically. Molecular subunits which were examined include hydrogen bridges (O - HċO), triiodide anions (I-3), other linear triatomic fragments (Cl - SbċCl, S - SċS, Mo - OċMo), tetrahedral ions (SO2-4, PO3-4, AlCl-4) and related species (MSO3, etc.), molecules containing both keto- and amino-groups (mostly alkaloids), substituted [10]annulenes and cycloheptatrienes, organic five-membered rings, and five-coordinated metal and nonmetal atoms. The bond distances and angles describing the structure of a giving fragment cover a range that is many times larger than the range of the experimental standard deviations. The changes of the various structural parameters of a fragment are correlated with each other. The observed mutual dependence (structural correlation) may be described by means of Pauling's equation relating bond length r to bond number n:r = r0 - clogn. The bond numbers n are expressed in terms of bond angles. The sum of bond numbers at a given atom is roughly constant and does not depend on the environment. “Standard bond lengths” of a fragment are determined by a least-squares procedure based on all available data. They are supplemented by curves that describe the observed distortions.The shape of these correlation curves is reminiscent of the structural changes occurring along the pathways of chemical reactions, e.g. nucleophilic substitution at tetrahedrally coordinated atoms (SN1 and SN2), nucleophilic addition to carbonyl groups, electrocyclic ring closure of polyenes, pseudo-rotation of five-membered rings or Berry pseudo-rotation. For many of these reactions approximate energy hypersurfaces have been obtained from quantum mechanical calculations, model force fields and from spectroscopic information (IR, NMR). Comparison between reaction pathways determined from structural correlations with those obtained from models of the energy surfaces shows fair agreement.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/anie.197504601
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    The Variety of Thermal Pericyclic Reactions (1974)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 13 (1974), S. 47-76 
    Details
    ISSN: 0570-0833
    Keywords: Pericyclic reactions ; Reaction mechanisms ; Woodward-Hoffmann rules ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The six-electron thermal pericyclic reactions are examined systematically as to the number and kind which are possible by varying both the σ shell and the combinations of different atoms in all orientations, on both a six-atom and a five-atom framework. A simple unifying nomenclature is offered for these reactions, which number in the thousands. Further, in order to comprehend this very large number of possible reactions, they are also organized systematically in terms of their value for basic synthesis operations: construction, elimination, refunctionalization, etc. The methodology is aimed at providing a basis of selection for the invention of useful new reactions. A discussion of reaction energetics leads also to an analysis of molecular features which can facilitate reaction.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/anie.197400471
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    The Theory of Pericyclic Reactions (1974)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 13 (1974), S. 751-780 
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    ISSN: 0570-0833
    Keywords: Pericyclic reactions ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pericyclic reactions include thermal and photochemical cycloadditions and cycloreversions, electrocyclic reactions and sigmatropic shifts. Configuration interaction analysis can be used for making predictions about preferred reaction pathways, about reaction rates, about the nature of possible intermediate steps, and above all about the stereochemistry of such reactions.
    Additional Material: 26 Ill.
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    URL: http://dx.doi.org/10.1002/anie.197407511
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    Kinetics and Mechanism of Radical Polymerization (1974)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 13 (1974), S. 781-789 
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    ISSN: 0570-0833
    Keywords: Kinetics ; Radical polymerization ; Polymerization ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Low molecular reactions are frequently accompanied by side reactions producing a whole spectrum of by-products whose removal in purification operations generally causes little difficulty because the major and side products usually differ sufficiently in their properties. Hence detailed kinetic studies in low molecular chemistry can claim industrial interest only insofar as they aim to reduce the rate of formation of side products. The situation is completely different in polymer chemistry, where the terms major and side product no longer apply. Instead, one obtains mixtures of similar and/or isomeric molecules which differ so little with regard to molecular weight and structure that resolution into pure substances or isolation of pure substances becomes practically impossible. However, since all partial reactions exert a direct influence on the product spread, i.e. the composition and properties of a product mixture are modified by any change in operating conditions, detailed kinetic analyses embracing all relevant partial reactions are an essential prerequisite for the production of defined polymeric products on any scale. This progress report illustrates the importance of kinetics for radical polymerization with the aid of selected examples.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/anie.197407811
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    Displacement Reactions of Phosphorus(V) Compounds and Their Pentacoordinate IntermediatesChemistry and Logical Structures, Part 5. - Part 4: see Ref. [2]. (1973)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 12 (1973), S. 91-119 
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    ISSN: 0570-0833
    Keywords: Displacement reactions ; Phosphorus ; Phosphorus ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of phosphorus(v) compounds involving the mutual interconversion of tetra- and pentacoordinate species are discussed in a critical review emphasizing stereochemical implications of the reaction mechanism. This discussion includes the formation and decomposition of the stable oxyphosphoranes, the Michaelis-Arbusov, Perkov, and Wittig reactions, interconversions of phosphines and their oxides, and the nucleophilic displacements on phosphonium compounds. Reactions of phosphate esters and related compounds receive particular attention. All chemical arguments are derived by considering the effect of factors determining the relative stabilities of phosphorane derivatives, their rates of formation, decomposition and rearrangement by bond deformation or rupture and recombination processes, considerations which are uniformly applied on the basis of concepts developed in a preceding communication[2]. It is shown that a comprehensive mechanistic interpretation of the foregoing reactions requires substantial addition to available conceptual foundations such that, in many cases, present concepts and mechanisms must be revised.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/anie.197300911
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    Mechanistic Analysis of Solution Reactions by Non-Isothermal Calorimetry (1973)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 12 (1973), S. 381-389 
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    ISSN: 0570-0833
    Keywords: Solution reactions ; Calorimetry ; Differential thermal analysis ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For the rapid kinetic and energetic analysis of reactions in solution (τ20°C 〉 10-4s) by differential thermal analysis (DTA), the following thermogram parameters are defined as characterizing the start of the reaction: 1. initial temperature, 2. activation energy of the initiation reaction. In conjunction with the shape index (asymmetry of the DTA curve) and the half width of the DTA curve referred to standard physical conditions (cell constant, heating rate, and temperature difference), these quantities allow a simple distinction between one-step reactions of first and second order and composite reactions. It is possible to recognize whether a process involves parallel, successive, or equilibrium reactions, or combinations of these. The reaction mechanism can be clarified in many cases by measurements at various concentrations and heating rates and by discussion of the enthalpy values. The shortened method described in this report for the evaluation of the thermograms was derived with the aid of an analog computer and checked experimentally.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/anie.197303811
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    Mechanisms of Reactions in the Solid State (1972)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 11 (1972), S. 173-179 
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    ISSN: 0570-0833
    Keywords: Solid-state reactions ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of two solid phases X and Y to give a solid compound XYv is taken as an example for the discussion of transport mechanisms and reaction steps. The following methods of investigation are discussed: determination of the rate law, marker experiments, and calculation of the reaction rate. It is pointed out that the investigation of powder reactions leads to problematic conclusions.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/anie.197201731
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    The Mechanism of Contact Elimination, A Contribution to Understanding the Function of Polar Catalysts (1971)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 10 (1971), S. 172-181 
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    ISSN: 0570-0833
    Keywords: Contact elimination ; Elimination ; Reaction mechanisms ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The current ideas of organic chemists based on the work of Ingold and his school are applied to heterogeneous catalytic eliminations (mostly from haloalkanes and aliphatic alcohols). It is deduced from the activity of the catalysts, the reactivity of the substrates (reactants), and the primary product distribution that these eliminations proceed by a heterolytic mechanism similar to that involved in the liquid phase. The activity of the catalysts (salts and oxides) increases with increasing charge and decreasing radius of the cations and with increasing basicity of the anions. The reactivity of the substrates behaves in much the same manner as in the liquid phase. In contrast with the liquid-phase reaction, the cis-olefins are frequently favored as primary products. The stereospecificity of the reaction is determined from the relative strengths of the interactions between the catalyst cation and the leaving group X-, and between the catalyst anion and the leaving proton. Only trans elimination has so far been found in the concerted mechanism.
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    URL: http://dx.doi.org/10.1002/anie.197101721
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    Kinetic Evidence for Reactive IntermediatesBased on a GDCh training course from October 6-9, 1969 in Munich. (1970)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 9 (1970), S. 751-762 
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    ISSN: 0570-0833
    Keywords: Intermediates ; Kinetics ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Spectroscopic methods have recently been developed that allow the direct detection of reactive intermediates under favorable circumstances. The most general and reliable method, however, is still the indirect one, which makes use of the priciple of kinetic competition; this method is based on the freedom of the intermediate to choose between several reaction possibilities. The following discussion is addressed less to the specialist in reaction mechanisms than to the outsider who wishes to obtain some idea of the value and limitations of the kinetic method.
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    The Conservation of Orbital SymmetryThis memoir will also be published as a separate brochure, copies of which can be ordered from Verlag Chemie GmbH, D-694 Weinheim, Postfach 129/149 (Germany), Academic Press Inc., 111 Fifth Avenue, New York, N.Y. 10003 (USA), or Academic Press Inc. Ltd., Berkeley Square House, Berkeley Square, London W. 1 (England), at a price of ca. DM 16.- or $ 4.40. A German version is also available from Verlag Chemie GmbH. (1969)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 8 (1969), S. 781-853 
    Details
    ISSN: 0570-0833
    Keywords: Conservation of orbital symmetry ; Orbital symmetry ; Bond theory ; Pericyclic reactions ; Electrocyclic reactions ; Reaction mechanisms ; Woodward-Hoffmann rules ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 44 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196907811
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    Mechanistic Organic Photochemistry (1969)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 8 (1969), S. 1-11 
    Details
    ISSN: 0570-0833
    Keywords: Photochemistry ; Rearrangement ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organic photochemical reactions can be understood as transformations of the electronically excited states of the reactant molecules. By considering Lewis structure or molecular orbital representations of these excited states it is possible to outline the several possible reactions available in the case of a given reactant. A number of different types of photochemical transformations are now reasonably well understood. In these cases one finds the same common controlling feature, namely the tendency for an excited state species to follow mechanistic pathways of minimum energy and the requirement for continuous electron redistribution in following these pathways. These preferred transformations can often be selected by inspection of relative bond orders for different types of bonding, by comparison of the potential energy surfaces available to the excited state molecules, and by use of correlation diagrams. The reactions derive from both singlet and triplet states, and one of the more reliable methods now available for identifying excited states reacting is termed the “fingerprint method”. Examples of the author's mechanistic approach are given both for ketone and for hydrocarbon photochemistry.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196900011
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    The Mechanism of the Wolff-Kishner Reduction, Elimination, and Isomerization ReactionsThis work is supported, in part, by the National Science Foundation, Grant GP-5739. (1968)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 7 (1968), S. 120-128 
    Details
    ISSN: 0570-0833
    Keywords: Reduction ; Elimination ; Isomerization ; Wolff-Kishner reaction ; Reaction mechanisms ; Hydrazones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanism of the Wolff-Kishner reaction is discussed in the light of accumulated information about the kinetics, thermodynamics, and solvent effects of the process. Wolff-Kishner reduction under normal conditions is thought to involve the trans hydrazone anion, which, in the rate-determining step, exhibits a more or less concerted proton capture at the carbanion terminal and undergoes a solvent-induced proton loss at the nitrogen terminal. The stereochemistry of the Wolff-Kishner reduction is believed to be affected by the presence of “ortho” substituents and by a change to a nonpolar, aprotic reaction medium. The mechanism elaborated for the Wolff-Kishner reduction is extended to the Wolff-Kishner elimination and isomerization reactions. Conformational analysis of the intermediates permits correlation of the competitive reduction and elimination processes with the structures of acyclic systems.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196801201
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    Diels-Alder reactions IIPart I see [2].: The Reaction Mechanism (1967)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 6 (1967), S. 16-33 
    Details
    ISSN: 0570-0833
    Keywords: Diels-Alder reaction ; Reaction mechanisms ; Cycloaddition ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The possible mechanisms of the preparatively so productive Diels-Alder reactions are discussed critically on the basis of experimental data. Although most of the facts can be explained readily by a synchronous mechanism, a number of problems remains.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196700161
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    Aromatic Fluorine as a Chemical Label for Detecting Reaction MechanismExtended version of a lecture presented at the 3rd International Fluorine Symposium, Munich, September 1965.BASED ON WORK CARRIED OUT WITH I. K. BARBEN, M. BELLAS, P. MILES, AND R. K. SMALLEY (1967)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 6 (1967), S. 596-607 
    Details
    ISSN: 0570-0833
    Keywords: Fluorine ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This article explains how nucleophilically activated fluorine can be used for the detection of ion-pair formation during the decomposition of various aryl radical generators. Thus a concurrent dual mechanism for the breakdown of certain aryl radical sources can be experimentally demonstrated by fluorine labeling. The bearing of this information on the mechanism of diazo coupling is also discussed.In addition, labeling with aromatic fluorine is applied to the thermolysis of aryl azides, the aminolysis of 3-aryl-4-bromosydnones, and the hydrolysis of 3-arylsydnone imines. Finally some mechanistic problems are posed which may possibly be solved by this labeling technique.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196705961
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    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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    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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    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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    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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    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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    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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    Fullerenes and their ions in hydrocarbon flames
    Amsterdam : Elsevier
    International Journal of Mass Spectrometry and Ion Processes 138 (1994), S. 133-148 
    Details
    ISSN: 0168-1176
    Keywords: Fullerenes ; Hydrocarbon flames ; REMPI ionization ; Reaction mechanisms
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0168-1176(94)04036-2
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    A spectrophotometric assay for the characterization of the S' subsite specificity of α-chymotrypsin
    Amsterdam : Elsevier
    Biochimica et Biophysica Acta (BBA)/Protein Structure and Molecular 869 (1986), S. 54-60 
    Details
    ISSN: 0167-4838
    Keywords: Chymotrypsin ; Nucleophile specificity ; Peptide synthesis ; Reaction mechanisms ; Spectrophotometric assay
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0167-4838(86)90309-2
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