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Course of Reactions

Figure A3.14.2. Characteristic features of a clock reaction, illustrated for the Landolt reaction, showing (a) variation of product concentration witii induction period followed by sharp reaction event (b) variation of overall reaction rate witli course of reaction. Figure A3.14.2. Characteristic features of a clock reaction, illustrated for the Landolt reaction, showing (a) variation of product concentration witii induction period followed by sharp reaction event (b) variation of overall reaction rate witli course of reaction.
One of the most original and significant ideas in organic chemistry was the suggestion by Hans Meerwein that carbocations (as we now call all the positive ions of carbon compounds) might be intermediates in the course of reactions that start from nonionic reactants and lead to nonionic covalent products. [Pg.73]

The best-known equation of the type mentioned is, of course, Hammett s equation. It correlates, with considerable precision, rate and equilibrium constants for a large number of reactions occurring in the side chains of m- and p-substituted aromatic compounds, but fails badly for electrophilic substitution into the aromatic ring (except at wi-positions) and for certain reactions in side chains in which there is considerable mesomeric interaction between the side chain and the ring during the course of reaction. This failure arises because Hammett s original model reaction (the ionization of substituted benzoic acids) does not take account of the direct resonance interactions between a substituent and the site of reaction. This sort of interaction in the electrophilic substitutions of anisole is depicted in the following resonance structures, which show the transition state to be stabilized by direct resonance with the substituent ... [Pg.137]

Experimental data that are most easily obtained are of (C, t), (p, t), (/ t), or (C, T, t). Values of the rate are obtainable directly from measurements on a continuous stirred tank reactor (CSTR), or they may be obtained from (C, t) data by numerical means, usually by first curve fitting and then differentiating. When other properties are measured to follow the course of reaction—say, conductivity—those measurements are best converted to concentrations before kinetic analysis is started. [Pg.688]

The concentration of oxidizing agents is essential for the course of reactions involving Eq. (2-9). These can be divided into two groups according to the type of oxidizing agent ... [Pg.35]

For a constant density system, the concentration of any species, K, Cp, during the course of reaction is given by... [Pg.520]

A. Haas, The General Course of Reactions and Structural Correlations in Sulfur-Nitr ogen Chemistry Discussed in Terms of Car bon and Sulfur(IV) Equivalence, J. Organomet. Chem., 623, 3 (2001). [Pg.12]

When a substrate enters the active site, charged groups may be forced to interact (unfavorably) with charges of like sign, resulting in electrostatic destabilization (Figure 16.6). The reaction pathway acts in part to remove this stress. If the charge on the substrate is diminished or lost in the course of reaction, electrostatic destabilization can result in rate acceleration. [Pg.506]

By the condensation of ethylideneacetophonone (109, R = Ph, R =Me) with acetophenone (110, lt"=Ph), the first unambiguous synthesis of 2,6-diphenyl-4-metliylpyrylium cliloroferrate was effected by Schneider and Ross, elucidating the course of reaction in Section II,D,2,a. [Pg.299]

Aromatic nitro compounds are hydrogenated very easily aliphatic nitro compounds considerably more slowly. Hydrogenations have been carried out successfully under a wide range of conditions including vapor phase (S9). Usually the goal of reduction is the amine, but at times the reduction is arrested at the intermediate hydroxylamine or oxime stage nitroso compounds never accumulate, although their transient presence may appreciably influence the course of reaction. In practice, nitro compounds often contain other reducible functions that are to be either maintained or reduced as well. [Pg.104]

Let s describe the course of reaction (5) in terms of a model. We will use methyl bromide to make the description simpler but the reaction of ethyl bromide is of the same type. [Pg.331]

Based on the successful series of transformations summarized in Scheme 1, Schreiber and Santini developed an efficient and elegant synthesis of periplanone B (1),8 the potent sex pheromone of the American cockroach, Periplaneta americana. This work constitutes the second total synthesis of periplanone B, and it was reported approximately five years after the landmark periplanone B synthesis by W.C. Still9 (see Chapter 13). As in the first synthesis by Still, Schreiber s approach to periplanone B takes full advantage of the facility with which functionalized 5-cyclodecen-l-one systems can be constructed via anionic oxy-Cope rearrangements of readily available divinylcyclohexanols.5 7 In addition, both syntheses of periplanone B masterfully use the conformational preferences of cyclo-decanoid frameworks to control the stereo- and regiochemical course of reactions carried out on the periphery of such ring systems.10... [Pg.335]

The ester functions can be replaced by alkylene (oligomethylene) groups without changing the course of reaction to give 4.142... [Pg.38]

A mixture of the a/J-unsaturated ester (14mmol), t-butyldimethylsilane (18 mmol) and tris(triphenylphosphine)rhodium(i) chloride (0.56 mmol) was placed in a pre-heated (100°C) oil bath, and the course of reaction monitored by i.r. spectroscopy. On completion (ca. 30 min) the product was isolated by direct distillation (60-88%). [Pg.62]

A solution of Pd(OAc)2 (0.05 mmol) and bis(diphenylphosphino)ethane (0.05 mmol) in acetonitrile (1 ml) was heated gently to reflux, at which time a solution of the silyl enol ether (1 mmol) and diallyl carbonate (2 mmol) in MeCN (4 ml) was added in one portion. The mixture was heated under reflux for 1-3 h, the course of reaction being monitored by t.l.c. or g.l.c. analysis. On completion, the cooled reaction solution was filtered through fluorosil. The pure a/ -unsaturated compound was isolated by column chromatography on silica gel (70-95%). [Pg.67]

The following assumptions are made (i) the activated complexes are in equilibrium with the reactants, (ii) the energy of a molecule is not altered when an activated complex is substituted for a nearest neighbour, and (iii) the products do not affect the course of reaction, except to define a boundary in surface processes. The various cases can be recognized from the magnitude of the pre-exponential term and calculated values [515] are summarized in Table 7. Low values of A indicate a tight surface complex whereas higher values are associated with a looser or mobile complex. [Pg.94]

Although thermodynamics can be used to predict the direction and extent of chemical change, it does not tell us how the reaction takes place or how fast. We have seen that some spontaneous reactions—such as the decomposition of benzene into carbon and hydrogen—do not seem to proceed at all, whereas other reactions—such as proton transfer reactions—reach equilibrium very rapidly. In this chapter, we examine the intimate details of how reactions proceed, what determines their rates, and how to control those rates. The study of the rates of chemical reactions is called chemical kinetics. When studying thermodynamics, we consider only the initial and final states of a chemical process (its origin and destination) and ignore what happens between them (the journey itself, with all its obstacles). In chemical kinetics, we are interested only in the journey—the changes that take place in the course of reactions. [Pg.649]

As already mentioned, complexes of chromium(iii), cobalt(iii), rhodium(iii) and iridium(iii) are particularly inert, with substitution reactions often taking many hours or days under relatively forcing conditions. The majority of kinetic studies on the reactions of transition-metal complexes have been performed on complexes of these metal ions. This is for two reasons. Firstly, the rates of reactions are comparable to those in organic chemistry, and the techniques which have been developed for the investigation of such reactions are readily available and appropriate. The time scales of minutes to days are compatible with relatively slow spectroscopic techniques. The second reason is associated with the kinetic inertness of the products. If the products are non-labile, valuable stereochemical information about the course of the substitution reaction may be obtained. Much is known about the stereochemistry of ligand substitution reactions of cobalt(iii) complexes, from which certain inferences about the nature of the intermediates or transition states involved may be drawn. This is also the case for substitution reactions of square-planar complexes of platinum(ii), where study has led to the development of rules to predict the stereochemical course of reactions at this centre. [Pg.187]

The importance of solvation on reaction surfaces is evident in striking medium dependence of reaction rates, particularly for polar reactions, and in variations of product distributions as for methyl formate discussed above and of relative reactivities (18,26). Thus, in order to obtain a molecular level understanding of the influence of solvation on the energetics and courses of reactions, we have carried out statistical mechanics simulations that have yielded free energy of activation profiles (30) for several organic reactions in solution (11.18.19.31. ... [Pg.211]

Although Ce(IV) oxidation of carboxylic acids is slow and incomplete under similar reaction conditions , the rate is greatly enhanced on addition of perchloric acid. No kinetics were obtained but product analysis of the oxidations of -butyric, isobutyric, pivalic and acetic acids indicates an identical oxidative decarboxylation to take place. Photochemical decomposition of Ce(IV) carbo-xylates is highly efficient unity) and Cu(ll) diverts the course of reaction in the same way as in the thermal oxidation by Co(IIl). Direct spectroscopic evidence for the intermediate formation of alkyl radicals was obtained by Greatorex and Kemp ° who photoirradiated several Ce(IV) carboxylates in a degassed perchloric acid glass at 77 °K in the cavity of an electron spin resonance spectro-... [Pg.385]

This has the attraction of explaining other characteristic features of this reaction, namely (i) the sensitivity to oxygen of the rate and course of reaction (because of capture of O2 by CH(C02H)2), (11) acceleration by added acrylonitrile to produce a carboxyl group-containing polymer, and (///) powerful induced oxidations by the reaction mixture of molecules inert to Mn(II[) pyrophosphate, e.g. ethanol, diethyl ether. [Pg.401]


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Course of a Catalytic Reaction

Course of the reaction

Factors Influencing the Course of Substitution Reactions

Stereochemical course of deamination reactions in acetic acid

Stereochemical course of nucleophilic substitution reactions

Surface on the Course of a Reaction

Time course of reaction

Unexpected Course of a Mannich Reaction in Alkaloid Synthesis

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