Intermediates terminology

So without direct amination we are confined to semi-direct ami-nation (Strike s terminology). In Strike s opinion, the direct addition of an azide (N3) counts. Once on the beta carbon, that azide is as good as an amine. But can we get an azide directly onto safrole without having to go thru the bromosafrole intermediate as was discussed earlier Maybe we can ... 

The initiators which are used in addition polymerizations are sometimes called catalysts, although strictly speaking this is a misnomer. A true catalyst is recoverable at the end of the reaction, chemically unchanged. Tliis is not true of the initiator molecules in addition polymerizations. Monomer and polymer are the initial and final states of the polymerization process, and these govern the thermodynamics of the reaction the nature and concentration of the intermediates in the process, on the other hand, determine the rate. This makes initiator and catalyst synonyms for the same material The former term stresses the effect of the reagent on the intermediate, and the latter its effect on the rate. The term catalyst is particularly common in the language of ionic polymerizations, but this terminology should not obscure the importance of the initiation step in the overall polymerization mechanism. 

Substituent effects on intermediates can also be analyzed by MO methods. Take, for example, methyl cations where adjacent substituents with lone pairs of electrons can form 71 bonds, as can be expressed in either valence bond or MO terminology. 

Substitution reactions by the ionization mechanism proceed very slowly on a-halo derivatives of ketones, aldehydes, acids, esters, nitriles, and related compounds. As discussed on p. 284, such substituents destabilize a carbocation intermediate. Substitution by the direct displacement mechanism, however, proceed especially readily in these systems. Table S.IS indicates some representative relative rate accelerations. Steric effects be responsible for part of the observed acceleration, since an sfp- caibon, such as in a carbonyl group, will provide less steric resistance to tiie incoming nucleophile than an alkyl group. The major effect is believed to be electronic. The adjacent n-LUMO of the carbonyl group can interact with the electnai density that is built up at the pentacoordinate carbon. This can be described in resonance terminology as a contribution flom an enolate-like stmeture to tiie transition state. In MO terminology,.the low-lying LUMO has a... 

The first step, which is rate determining, is an ionization to a carbocation (carbonium ion in earlier terminology) intermediate, which reacts with the nucleophile in the second step. Because the transition state for the rate-determining step includes R-X but not Y , the reaction is unimolecular and is labeled S l. First-order kinetics are involved, with the rate being independent of the nucleophile identity and concentration. 

The terminology describing the action of antioxidants is unfortunately not clear. Terms such as antioxidant power , antioxidant effectiveness , antioxidant ability , antioxidant activity , and antioxidant capacity are often used interchangeably and without discrimination. Here we use the term antioxidant activity as meaning a measure of the rate of antioxidant action, and the term antioxidant capacity as meaning a measure of the extent of antioxidant action, i.e. the amount of radicals or intermediates and products produced during oxidation that are quenched by a given antioxidant. Thus antioxidant activity is related to the kinetics of the antioxidant action and antioxidant capacity to the stoichiometry. 

In contrast to the transfer-dominated /-cat systems, the living systems comprise an ester and a third component, which hitherto has been called the activator . This term, however, is inadequate, because a survey of the field shows that in many systems the third component does not increase the reactivity of an ester, but diminishes it, or it may even convert a highly reactive cationic system to a more inert P-cat system giving living polymerisations. This distinction of the two types of third components , although implicit in the evidence, has not been made explicitly heretofore in our terminology. However, priority in this line of thought must be accorded to Faust et al. [8]. They realised that because in some systems an excess of base inhibits polymerisation, whereas in others an excess of base is necessary, two different reaction intermediates must be involved but they did not develop this theme. 

More recently, Shaik and co-workers used density functional theory as well as QM(DFT)/MM calculations to show a pathway from the peroxoferric intermediate (5a) via the hydroperoxoferric (5b) intermediate to compound I (6) (see Figure 7.14)." In Figure 7.16, using Shaik s terminology, the peroxoferric intermediate is labeled (1), the hydroperoxoferric intermediate is labeled (2), Cpd 0, and the ferryloxo intermediate is labeled (3), Cpd I. 

It is our intention to present strategies based on chemically induced phase separation (CIPS), which allow one to prepare porous thermosets with controlled size and distribution in the low pm-range. According to lUPAC nomenclature, porous materials with pore sizes greater than 50 nm should be termed macroporous [1]. Based on this terminology, porous materials with pore diameters lower than 2 nm are called microporous. The nomination mesoporous is reserved for materials with intermediate pore sizes. In this introductory section, we will classify and explain the different approaches to prepare porous polymers and to check their feasibility to achieve macroporous thermosets. A summary of the technologically most important techniques to prepare polymeric foams can be found in [2,3]. 

At low pH (acidic solution), an amino acid will exist as the protonated ammonium cation, and at high pH (basic solution) as the aminocarboxylate anion. The intermediate zwitterion form will predominate at pHs between these extremes. The uncharged amino acid has no real existence at any pH. It is ironic that we are so familiar with the terminology amino acid, yet such a structure has no real existence Amino acids are ionic compounds, solids with a high melting point. 

Now, just the same sort of rationalization can be applied to the radical addition, in that the more favourable secondary radical is predominantly produced. This, in turn, leads to addition of HBr in what is the anti-Markovnikov orientation. The apparent difference is because the electrophile in the ionic mechanism is a proton, and bromide then quenches the resultant cation. In the radical reaction, the attacking species is a bromine atom, and a hydrogen atom is then used to quench the radical. This is effectively a reverse sequence for the addition process but, nevertheless, the stability of the intermediate carbocation or radical is the defining feature. The terminologies Markovnikov or anti-Markovnikov orientation may be confusing and difficult to remember consider the mechanism and it all makes sense. 

A similar aldol reaction is encountered in the Krebs cycle in the reaction of acetyl-CoA and oxaloacetic acid (see Section 15.3). This yields citric acid, and is catalysed by the enzyme citrate synthase. This intermediate provides the alternative terminology for the Krebs cycle, namely the citric acid cycle. The aldol reaction is easily rationalized, with acetyl-CoA providing an enolate anion nucleophile that adds to the carbonyl of oxaloacetic acid. We shall see later that esters and thioesters can also be converted into enolate anions (see Section 10.7). 

The Krebs cycle intermediate that reacts with acetyl-CoA is oxaloacetate, and this reacts via an aldol reaction, giving citryl-CoA. However, the enzyme citrate synthase also carries out hydrolysis of the thioester linkage, so that the product is citrate hence the terminology citric acid cycle . The hydrolysis of the thioester is actually responsible for disturbing the eqnilibrinm and driving the reaction to completion. 

The manifold intermediates in homogeneous transition-metal catalysis are certainly metal complexes and therefore show a behaviour like ordinary coordination compounds associations of phosphorus donors open up multifarious additional controls. Both, substrates and P ligands are Lewis bases that we have to consider and that compete at the coordination centers of the metal, leading to competitive, non-competitive or uncompetitive activation or inhibition processes in analogy to the terminology of enzyme chemistry... 

Two types of precision are usually distinguished, namely the repeatability and the reproducibility. Repeatability is the precision obtained in the best possible circumstances (same analyst, one instrument, within one day when possible) and reproducibility under the most adverse possible circumstances (different laboratories, different analysts, different instruments, longer periods of time, etc.). Reproducibility can be determined only with interlaboratory experiments. Intermediate situations may and do occur. They are for instance defined in terms of M-factor-different intermediate precision measures, where M is one, two, three or even higher [8,9]. In this definition M refers to the number of factors that are varied to make the estimation. The most likely factors to be varied are time, analyst and instrument. According to this terminology, one estimates e.g. the time-and-analyst-different intermediate precision measure (M=2), when the precision is determined by measuring a sample over a longer period of time in one laboratory by two analysts with one instrument. 

The symbol / in system (26) refers to an active surface site on the catalyst. Every species with / in it is an intermediate and the rest are terminal species. For the purpose of our analysis we could omit / wherever it appears alone as a reactant. Notice that by including it as an intermediate, we get a case of a system where H < I, or in Horiuti s terminology, the intermediates are not all independent. 

In some cases in which the Caro s acid oxidation of amines was not satisfactory, the corresponding hydroxylamines have been oxidized with acidified dichromate solutions [42], Both aliphatic and aromatic nitroso compounds have been prepared by this method [17, 42, 82, 90]. Frequently the reaction mixture from the reduction of a nitro compound is treated directly with the oxidizing medium without the isolation of the intermediate hydroxylamine. The method has been called the nitro reduction oxidation technique, [82] a terminology we cannot condone. 

The formal terminology which had been used for the intermediates is analogous to those of bacteriorhodopsin. 

For a single substrate-single product reaction with one path (assume path A is insignificant), the pH dependence of ka/Ka reflects the ionization of groups on the free enzyme (Ka, Kb) and free substrate and is not affected by any of the intermediates. The pH dependencies of ka and Kb separately are more complicated and, as well as Kb and Kb, involve KJ and Kb which depend on the number of intermediates and steady state rate constants. Using the terminology of del Rosario and Hammes (499). 

It was suggested that for hydrogen peroxide, the reaction begins with the addition of the HOCT anion, followed by formation of the cationic intermediate 216. According to terminology, such a mechanism, which implies the presence of intermediate 105, may be called orf/io-bridging or ortho-cyclization (84UK1648), as it was described for the reaction of 2-benzopyrylium salts with sodium azide (Section III,C,2). 

Experimental data from nucleophilic substitution reactions on substrates that have optical activity (the ability to rotate plane-polarized light) shows that two general mechanisms exist for these types of reactions. The first type is called an S 2 mechanism. This mechanism follows second-order kinetics (the reaction rate depends on the concentrations of two reactants), and its intermediate contains both the substrate and the nucleophile and is therefore bimolecular. The terminology S 2 stands for substitution nucleophilic bimolecular. ... 

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