Mechanism classification substitution

Classification of the ligand substitution mechanisms is given in Table 7.2a. 

The mechanism classification and the overall transformation classification are orthogonal to each other. For example, substitution reactions can occur by a polar acidic, polar basic, free-radical, pericyclic, or metal-catalyzed mechanism, and a reaction under polar basic conditions can produce an addition, a substitution, an elimination, or a rearrangement. Both classification schemes are important for determining the mechanism of a reaction, because knowing the class of mechanism and the overall transformation rales out certain mechanisms and suggests others. For example, under basic conditions, aromatic substitution reactions take place by one of three mechanisms nucleophilic addition-elimination, elimination-addition, or SrnL If you know the class of the overall transformation and the class of mechanism, your choices are narrowed considerably. 

Kinetic Consequences of Reaction Pathways 441 TABLE 12.2 Classification of Substitution Mechanisms for Octahedral Complexes... 

Langford and Gray presented another classification for the mechanism of substitution reactions that is particularly appropriate for metal complexes [5], but also englobes the classification of Ingold and co-workers for organic substitutions. This classification makes a distinction between the stoichiometric mechanism and the activation mechanism. The stoichiometric mechanism concerns the nature of the intermediate. It distinguishes between ... 

A more detailed classification of chemical reactions will give specifications on the mechanism of a reaction electrophilic aromatic substitution, nucleophilic aliphatic substitution, etc. Details on this mechanism can be included to various degrees thus, nucleophilic aliphatic substitutions can further be classified into Sf l and reactions. However, as reaction conditions such as a change in solvent can shift a mechanism from one type to another, such details are of interest in the discussion of reaction mechanism but less so in reaction classification. 

But Ingold s triumph came in finally seeing the advantages of Robinson s explanation system, revising it, and substituting a new and clearer language and classification of types of reaction mechanisms. Lapworth, Robinson, and their collaborators referred to Ingold s "conversion" experience, a conversion in which Paul eventually helped create the myth of his role not as saint but as savior. 

Other terms that he invented include the system of classification for mechanisms of aromatic and aliphatic substitution and elimination reactions, designated SN1, SN2, El, and E2. "S" and "E" refer to substitution and elimination, respectively, "N" to nucleophilic, and "1" and "2" to "molecularity," or the number of molecules involved in a reaction step (not kinetic order, having to do with the equation for reaction rate and the concentration of reactants). Ingold first introduced some of these ideas in 1928 in a... 

The basic classification of nucleophilic substitutions is founded on the consideration that when a new metal complex is formed through the breaking of a coordination bond with the first ligand (or water) and the formation of a new coordination bond with the second ligand, the rupture and formation of the two bonds can occur to a greater or lesser extent in a synchronons manner. When the mpture and the formation of the bonds occur in a synchronous way, the mechanism is called substitution nucleophilic bimolecular (in symbols Sn2). On the other extreme, when the rupture of the first bond precedes the formation of the new one, the mechanism is called substitution nucleophilic unimolecular (in symbols SnI). Mechanisms Sn2 and SnI are only limiting cases, and an entire range of intermediate situations exists. 

Langford and Gray proposed in 1965 (13) a mechanistic classification for ligand substitution reactions, which is now generally accepted and summarized here for convenience. In their classification they divided ligand substitution reactions into three categories of stoichiometric mechanisms associative (A) where an intermediate of increased coordination number can be detected, dissociative (D) where an intermediate of reduced coordination number can be detected, and interchange (I) where there is no kinetically detectable intermediate [Eqs. (2)-(4)]. In Eqs. (2)-(4), MX -i and... 

CLASSIFICATION OF SUBSTITUTED BENZOYL CHLORIDES ACCORDING TO THE PREDOMINANT MECHANISM OF HYDROLYSIS... 

It should be remembered that the classification criterion used above has nothing to do with the fact that the composition of the products may indicate that an atom or group has been transferred between the two metal centers. An inner-sphere mechanism may or may not be accompanied by atom or group transfer, and this may either occur as a consequence of the transition state structure or trivially be due to the fact that the complexes involved are substitution labile, i.e. exchange of ligands between themselves or the environment takes place at a rate faster than that of electron transfer. 

Chintakunta VK, Akella V, Vedula MS et aL (2002) 3-0-Substituted benzyl pyrazidone derivatives as COX inhibitors. Eur J Med Chem 37 339-347 Coleman RA, Smith WL, Narumiya S (1994) VIII. International union of pharmacology classification of prostanoid receptors Properties, distribution, and structure of the receptors and their subtypes. Pharmacol Rev 46 205-229 Copeland RA, Williams JM, Giannaras J et al. (1994) Mechanism of selective inhibition of the inducible isoform of prostaglandin G/H synthase. Proc Natl Acad Sd USA 91 11202-11206... 

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