Reaction classification elimination reactions

As we have seen (Section 4, p. 191) the range of effective molarities associated with ring-closure reactions is very much greater than that characteristic of intramolecular general acid-base catalysis the main classification is therefore in terms of mechanism. By far the largest section (I, Tables A-D) gives EM s for intramolecular nucleophilic reactions. These can be concerted displacements (mostly at tetrahedral carbon), stepwise displacements (mostly addition-elimination reactions at trigonal carbon), or additions, and they have been classified in terms of the nucleophilic and electrophilic centres. 

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 rationale of classification by reaction types is that different functional groups may show the same kinds of reactions. Thus, as we have just seen, alcohols, carboxylic acids, and amines all can accept a proton from a suitably strong acid. Fortunately, there are very few different types of organic reactions — at least as far as the overall result that they produce. The most important are acid-base, substitution, addition, elimination, and rearrangement reactions. Some examples of these are given below, and you should understand that these are descriptive of the overall chemical change and nothing is implied as to how or why the reaction occurs (also see Section 1-11). 

Monte Carlo modeling predicts a- and d-activated water exchange on [Ln(H20)8]3+ and [Ln(H20)9]3+, respectively.290 Molecular dynamic simulations of water exchange on [Nd(H20)9]3+ and [Yb(H20)8]3+ indicate the operation of Id and Ia mechanisms, respectively, but the equilibrium between [Sm(H20)9]3+ and [Sm(H20)8]3+ is maintained by a ninth water molecule that exchanges rapidly between the first coordination sphere and the bulk in an alternation of addition and elimination reactions that does not readily fit into the a- and d-activation classifications.211... 

Figure 7.11 shows the distribution of reactions in each classification that satisfy the criteria AE(min) > 0.6 (minimum atom economy above 60%), /(sac)(max) = 0 (no sacrificial reagents used), and both constraints. Not surprisingly, the best performing reaction classifications are multicomponent reactions and condensations. The worst performers are the redox reactions and eliminations. Most rearrangements, non-carbon-carbon bond forming reactions, and substitutions satisfy the condition/(sac)(max) = 0. 

We can distinguish three general classifications of elimination reactions on the basis of the timing of these processes, and transition structures for each are... 

HORACE used alternating phases of classification (which topological or physicochemical features are required for a reaction type) and generalization (which features are allowed and can be eliminated) to produce a hierarchical classification of a set of reaction instances. 

Kinds of Catalyzed Organic Reactions A fundamental classification of organic reactions is possible on the basis of the lands of bonds that are formed or destroyed and the natures of eliminations, substitutions, and additions of groups. Here a more pragmatic hst of 20 commercially important lands or classes of reactions will be discussed. In all instances of sohd-catalyzed reactions, chemisorption is a primary step. Often molecules are dissociated on chemisorption into... 

Carbanions can take part in most of the main reaction types, e.g. addition, elimination, displacement, rearrangement, etc. They are also involved in reactions, such as oxidation, that do not fit entirely satisfactorily into this classification, and as specific—ad hoc—intermediates in a number of other processes as well. A selection of the reactions in which they participate will now be considered many are of particular synthetic utility, because they result in the formation of carbon-carbon bonds. 

The first step is carbon-metal bond formation via coordination. This process may be followed by one or more steps, leading to transformation of ligands and/or reaction between ligands. In a final step, the metal is removed from the organic moiety. Reactions are catalytic or stoichiometric, depending on whether or not the metal is eliminated in its original oxidation state. The following is a broad classification of these processes. 

The development of polymer science with the study of new polymerization processes and polymers showed that the original classification by Carothers was not entirely adequate and left much to be desired. Thus, for example, consider the polyurethanes, which are formed by the reaction of diols with diisocyanates without the elimination of any small molecule ... 

---