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  • 1990-1994  (4)
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  • 1994  (4)
  • Reaction mechanisms
  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 261-265 
    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
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 33 (1994), S. 938-957 
    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
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 33 (1994), S. 255-276 
    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
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 33 (1994), S. 294-302 
    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
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