Characterization of intermediates

Modified rhodium systems show considerable activity in the hydroformylation of styrene to the branched aldehydes. Chiral diphosphines, diphosphites, and phosphine-phosphites have been the ligands most studied. Hydroformylation experiments have often been performed in situ but the characterization of intermediates has provided an interesting contribution to coordination chemistry.179... 

The kinetics and mechanisms of template reactions are rarely studied in depth - they are often merely assumed to be genuine template reactions rather than a metal-activated reaction at a coordinated ligand. The best evidence for a true template mechanism is the isolation and characterization of intermediates with both reactants and with the macrocyclic product complexed with the template cation. 

Inert centers facilitate the detection and characterization of intermediates. Recently investigated systems involving cobalt(III) complexes include [Co(L)(OH)(H20)]2+-promoted hydrolysis of 2,4-dinitrophenyl... 

An important tool for the fast characterization of intermediates and products in solution-phase synthesis are vibrational spectroscopic techniques such as Fourier transform infrared (FTIR) or Raman spectroscopy. These concepts have also been successfully applied to solid-phase organic chemistry. A single bead often suffices to acquire vibrational spectra that allow for qualitative and quantitative analysis of reaction products,3 reaction kinetics,4 or for decoding combinatorial libraries.5... 

Abstract This chapter presents the latest achievements reported in the asymmetric hydroformylation of olefins. It focuses on rhodium systems containing diphosphites and phosphine-phosphite ligands, because of their significance in the subject. Particular attention is paid to the mechanistic aspects and the characterization of intermediates in the hydroformylation of vinyl arenes because these are the most important breakthroughs in the area. The chapter also presents the application of this catalytic reaction to vinyl acetate, dihydrofurans and unsaturated nitriles because of its industrial relevance. 

Spectral resolution records spectra at different potentials, for example, during a CV scan. This allows structural characterization of intermediates. 

A frequent complication in the use of an insoluble polymeric support lies in the on-bead characterization of intermediates. Although techniques such as MAS NMR, gel-phase NMR, and single bead IR have had a tremendous effect on the rapid characterization of solid-phase intermediates [27-30], the inherent heterogeneity of solid-phase systems precludes the use of many traditional analytical methods. Liquid-phase synthesis does not suffer from this drawback and permits product characterization on soluble polymer supports by routine analytical methods including UV/visible, IR, and NMR spectroscopies as well as high resolution mass spectrometry. Even traditional synthetic methods such as TLC may be used to monitor reactions without requiring preliminary cleavage from the polymer support [10, 18, 19]. Moreover, aliquots taken for characterization may be returned to the reaction flask upon recovery from these nondestructive... 

NMR and UV-visible techniques have been used in the characterization of intermediates in the [Fe (edta)]" -promoted decomposition of hydrogen peroxide7 Fe complexes of edta, nta, and dtpa react with FISOs by an inner-sphere one-electron transfer mechanism with transient production of S04, in contrast to Cu, which reacts by an outer-sphere mechanism to give S04 and hydroxy radicalsFe -edta redox properties are relevant to Fe /Cu /H202 systems. ... 

In addition to characterization of intermediates, in situ spectroscopic techniques can be applied in kinetic studies, providing additional mechanistic insight. Also, isotopic labeling studies have proven very useful, especially vhen studying the individual steps of a catalytic cycle [5, 6]... 

There are also tremendous possibilities for using RDCs as a direct probe of conformational dynamics. Recalcitrant problems such as the characterization of intermediate timescale motions (microsecond-nanosecond), both for... 

Characterization of Intermediate Fractions. Nonaqueous poten-tiometric titration was used to characterize the nitrogen compounds in three intermediate fractions from the production of the syncrude. Table VII lists these three fractions, their source, and the titration results. Also... 

Liu, K.E., Valentine, A.M., Wang, D., Huynh, B.H. Edmondson, D.E. Salifoglou, A. Lippard, SJ. (1995) Kinetic and spectroscopic characterization of intermediates and component interactions in reactions of methane monooxygenase from Methylococcus capsulatus (Bath), J. Am. Chem. Soc. 117, 10174-10185. 

The facile iodination of organocopper compounds (79) is a useful reaction for the characterization of intermediate copper compounds which are formed by addition or insertion reactions 61, 223, 294, 304). Bromine has also been used 223, 294), but the yields may be low ( 15%) compared with iodolysis, because of bromine s ability to function as an oxidant 223). 

The cleavage and characterization of intermediates or final compounds, as for off-bead reaction monitoring (Section 1.3.2), are the most reliable methods to quantify the outcome of an SPS. The final target molecule on SP has to be cleaved into solution so that it can be characterized by classical off-bead methods. The synthetic intermediates obtained after each SPS step can also be characterized off-bead when the cleavage conditions do not affect their structure and when the amount of resin beads lost during the characterization process is negligible. 

Biosynthesis. Full details of the isolation and characterization of intermediates in the biosynthesis of ubiquinone-8 (233) in E. coli have been described. Two review articles deal with the compartmentation of the biosynthesis of aromatic amino-acids and prenylquinones in higher plants and the regulation of prenylquinone biosynthesis by tyrosine. ... 

Hi. Characterization of intermediate II. McCapra and Hysert (1973) have suggested that intermediates I and II (see Fig. 42) could be the same and should both be identified with the luciferase-bound reduced flavin. It was initially postulated (Hastings and Gibson, 1963) that the combination of luciferase with reduced flavin in the absence of oxygen forms a complex (intermediate I), which in the presence of oxygen has only a transient existence. Therefore oxygen-free mixtures of reduced flavin and luciferase were prepared and exam-... 

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