Chemical intermediate definition

RNA is the only macromolecule known to have a role both in the storage and transmission of information and in catalysis, which has led to much speculation about its possible role as an essential chemical intermediate in the development of life on this planet. The discovery of catalytic RNAs, or ribozymes, has changed the very definition of an enzyme, extending it beyond the domain of proteins. Proteins nevertheless remain essential to RNA and its functions. In the modem cell, all nucleic acids, including RNAs, are complexed with proteins. Some of these complexes are quite elaborate, and... 

In the literature on chemistry and biochemistry, in particular in the cited statements from Lehninger s textbook, the intermediate substance of the second kind is identified with highly reactive particles (intermediate products of the first kind). This mistake is based on fuzziness of the chemical induction definition and identification of conjugated reactions with consecutive ones. As a result, Lehninger has concluded that the energy transfer via general intermediate product is the universal property of consecutive reactions. ... 

If the /ill potential of the reaction is known, it can always be estimated if the work produced by it is sufficient for performing another, non-spontaneous reaction, i.e. reaching a definite final state of the system. However, the /ill potential may not relate to the realization of a particular chemical mechanism and the notion of chemical intermediate associated with it. Therefore, identification of the /ill potential with the notion of intermediate is, to choose our words carefully, incorrect and, in this connection, we may scarcely agree with the experts in bioenergetics that the /2H potential is the conjugation intermediate. 

Polypropylene glycol (9) PPG 400 Definition Polymer of propylene oxide Formula H(OCH2CHCH3)nOH, avg. n = 9 Properties Nonionic Toxicology TSCA listed Uses Chemical intermediate intermediate yielding esters useful as lubricants, defoamers in rubber, pharmaceuticals antifoam in fermentation and paints antiblooming agent for pentachlorophenol-treated wood binder and lubricant for ceramics plasticizer of resin-treated papers mold release applies. emollient, solvent in cosmetics, pharmaceuticals boiler water additive (food contact) in food-pkg. adhesives Features Provides low odor, low irritation, low toxicity to personal care prods. 

Synonyms 1,3-Bis (2-hydroxypropoxy) benzene Definition Hydroxypropyl ether of resorcinol Toxicology Eye irritant Uses Chemical intermediate processing aid and chain extender for PU elastomers Trade Name Synonyms HPR [Indspec... 

Definition Mixture of syn. fatty alcohols with 20-40 carbons in the alkyl chain Uses Antioxidant heat stabilizer UV stabilizer vise, depressant emulsifier in cosmetics emollient protective f Im-former for skin care prods, food-pkg. adhesives chemical intermediate for oxidation, ethoxylation, sulfation, amination, esterification coemulsifier and direct additive in coatings processing aid, lubricant, dispersant in plastics... 

One definite disadvantage that the Organic Chemicals Department had was that during the 1960s it was involved in several totally unrelated businesses (fluorocarbons, petroleum additives, dyes and chemical intermediates). When people were transferred from one area to another, they brought little useful experience with them. There was reputedly some crossfertilization, but it did not do much for moving businesses along. DuPont then was reluctant... 

The chemical and physical properties of the polymers obtained by these alternate methods are identical, except insofar as they are affected by differences in molecular weight. In order to avoid the confusion which would result if classification of the products were to be based on the method of synthesis actually employed in each case, it has been proposed that the substance be referred to as a condensation polymer in such instances, irrespective of whether a condensation or an addition polymerization process was used in its preparation. The cyclic compound is after all a condensation product of one or more bifunctional compounds, and in this sense the linear polymer obtained from the cyclic intermediate can be regarded as the polymeric derivative of the bifunctional monomer(s). Furthermore, each of the polymers listed in Table III may be degraded to bifunctional monomers differing in composition from the structural unit, although such degradation of polyethylene oxide and the polythioether may be difficult. Apart from the demands of any particular definition, it is clearly desirable to include all of these substances among the condensation... 

Where is the dividing line between bulk and fine chemicals Here again there is no universally accepted definition. Nonetheless, a useful definition of a fine chemical is one with a price of more than 10 US dollars/kg and a volume of less than 10,000 tons per annum. The latter is rather a large volume for most fine chemicals, e.g. most pharmaceutical intermediates are produced in quantities of less than 100 tons per annum. In practice, the type of technology used is probably more dictated by volume than by product application. 

The textbook definition of a reactive intermediate is a short-lived, high-energy, highly reactive molecule that determines the outcome of a chemical reaction. Well-known examples are radicals and carbenes such species cannot be isolated in general, but are usually postulated as part of a reaction mechanism, and evidence for their existence is usually indirect. In thermal reactivity, for example, the Wheland intermediate (Scheme 9.1) is a key intermediate in aromatic substitution. 

Reaction mechanisms in chemistry are often written as a sequence of chemical structures, and such structures are referred to as reactive intermediates. Indeed, these intermediates often correspond to local minima on the potential energy curve—as shown in Figure 9.1—but need not do so, and the definition of a reactive intermediate... 

The chemical behavior of ions, ion pairs, and polarizable molecules partakes of the same indistinctness as the definitions of these species. Any attempt to make a complete catalog of the reactions of ions will almost certainly include borderline reactions whose intermediates are in fact ion-pairs or even covalent molecules. For many purposes the identification of a reaction as carbonium ion-like, or what the Germans would call Krypto-ionenreaktion, is as useful as the certain knowledge that the intermediate is actually a carbonium ion. Many of the ionic reaction mechanisms in the literature do not represent actual free ions and were not so intended by their authors. The ionic representation is often merely a convenient simplification if it is an oversimplification it is one that is easily rectified when the pertinent data become available. The value of such approximate mechanisms is that... 

Many issues in one management area are bound to affect performance in other areas. For example, an inherent safety review may propose a change in the process chemistry that will allow a definite reduction in chemical reactivity hazards, perhaps by eliminating a reactive intermediate. Such changes will have to fit with product quality requirements, and the customer may need to be included in the process of changing to the inherently safer alternative. Effective communication among all parts of the management team will avoid many problems and help identify what works best. 

A series of observations in which the presence of an apparently unaffected substance initiated the progress of a chemical reaction prompted the Swedish chemist Berzelius in 1835 to introduce the term catalyst , but it was only towards the end of the last century that a dear definition could be given by Ostwald, namely a catalyst is a substance which affects the rate of a chemical reaction without appearing in the final products . This is achieved through the formation of intermediate compounds between the catalyst and the molecules involved in the reaction whereby an alternative path is offered which may be passed through with higher probability, i.e. 

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