General reaction features

2 Reactions of Dinuclear Propargylium Complexes with Nucleophiles 4.4.3.2.1 General Reaction Features 

5-dimethyl-3-hepten-2-one) [151], acetylenic analogs of leukotriene-E4 [152], 16a, 17a-epox-ycorticosterone [153], and the side chain of isolaurepinnacin [154], 

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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. 

Reactions can be considered as composite systems containing reactant and product molecules, as well as reaction sites. The similarity of chemical structures is defined by generalized reaction types and by gross structural features. The similarity of reactions can be defined by physicochemical parameters of the atoms and bonds at the reaction site. These definitions provide criteria for searching reaction databases [23],... 

All the reactions discussed in this review are aromatic nucleophilic substitutions in the ordinary sense. These reactions are briefiy described in the following sections with respect to their general kinetic features and mainly involve aza-activated six-membered ring systems, although a few studies of other heteroaromatic compounds are also available. 

The general mechanistic features of the aldol addition and condensation reactions of aldehydes and ketones were discussed in Section 7.7 of Part A, where these general mechanisms can be reviewed. That mechanistic discussion pertains to reactions occurring in hydroxylic solvents and under thermodynamic control. These conditions are useful for the preparation of aldehyde dimers (aldols) and certain a,(3-unsaturated aldehydes and ketones. For example, the mixed condensation of aromatic aldehydes with aliphatic aldehydes and ketones is often done under these conditions. The conjugation in the (3-aryl enones provides a driving force for the elimination step. 

The model proposed by Brandt et al. is consistent with the experimental observations, reproduces the peculiar shape of the kinetic curves in the absence and presence of dioxygen reasonably well, and predicts the same trends in the concentration dependencies of t, p that were observed experimentally (80). It was concluded that there is no need to assume the participation of oxo-complexes in the mechanism as it has been proposed in the literature (88-90). However, the model provides only a semi-quantitative description of the reaction because it was developed at constant pH by neglecting the acid-base equilibria of the sulfite ion and the reactive intermediates, as well as the possible complex-formation equilibria between various iron(III) species. In spite of the obvious constraints introduced by the simplifications, the results shed light on the general mechanistic features of the reaction and could be used to identify the main tasks for further model development. 

A large number of ligand reactions exist where both the kinetic patterns and the general mechanistic features are modified, rather than destroyed, by coordination. These reactions can furnish much information on the way coordination per se will affect the kinetic and thermodynamic aspects of a reaction. Generally, these will be reactions where specific redox properties of the central ion are not involved. In many of these cases coordination can provide a rational basis for the modification of synthetic procedures. 

A second general approach featuring the use of C2 symmetric diols as chiral auxiliaries was developed by Mash (equation The reaction proceeded with good to excel-... 

Whatever method is used, the replacement of an amino group by fluorine, via a diazo derivative, implies two reaction steps diazotization (to give 1) and dediazoniation (to give 2). The diazo intermediate can be isolated or not depending upon the substrate, the reagents, and the reaction conditions however, some general mechanistic features are common to all cases. 

One embodiment of this general reaction led to a product which was commercially produced for several years by Stauffer as Fyrol 76 (9), a copolycondensation product of dimethyl methyl-phosphonate with bis(2-chloroethyl) vinylphosphonate. The features of Fyrol 76 were high phosphorus content (20%), water solubility, and ability to be polymerized by means of a radical initiator to a crosslinked polymer. A related polycondensation product was developed from tris(2-chloroethyl) phosphate and dimethyl methylphosphonate. By control of the reagents and procedure used for neutralization, these oligomeric products were produced with primary alcohol functional groups (7). 

To begin the exploration of actual reaction pathways in complex pyrolyses of aromatic substances, we have carried out a detailed experimental and theoretical analysis of the liquid-phase pyrolysis of bibenzyl. This pyrolysis system has been studied by others (44,45,46), and the general kinetic features of this reaction system are now rather well agreed on. Complete details of this work will appear elsewhere (38a) and a few implications of this work of particular relevance to coal reactions will be discussed here. 

The establishment of the main features of the reactions of carboxylate ions with 3-unsubstituted isoxazolium salts is fully described in the classic paper by Woodward and Olofson.165 A generalized reaction scheme is shown as Scheme 10. Deprotonation at the 3-position is rapidly followed (or more probably accompanied) by ring opening to give the ketoketenimine (54). Ketoketenimines have been detected spectroscopically and are sufficiently stable for isolation in some cases.166,167 Reaction of carboxylic acid... 

A variety of spectroscopic techniqnes has made invalnable contribntions to nnderstanding the stmcture and reactions of organoberyllium and -magnesinm componnds. In this section, general spectroscopic features will be discussed, but their applications will not be detailed. 

This topic has been discussed in a review on rearrangements of sulfones129. The first attempts to thermally convert allylic sulfinates to sulfones were reported as early as 1950130. Later, it was demonstrated that this rearrangement is a general reaction occurring under thermal or solvolytic conditions and the mechanistic and stereochemical features of this conversion were elucidated. 

We begin our discussion of the chemical reactions of alcohols, ethers, and epoxides with a look at the general reactive features of each functional group. 

Figure 24.6 compares the general reaction for nucleophilic substitution of an ester with the Claisen reaction. Sample Problem 24.3 reinforces the basic features of the Claisen reaction. 

A general characteristic feature of the H2PtCl6-solvent catalytic system is the induction period which is followed by a fast exothermic reaction. Recent studies... 

Wiesner discovered that the photoreaction of an allene to an a/J-unsaturated ketone always shows the regioselectivity illustrated in the example (487 — 488) above. The general reaction shows another interesting feature in polycyclic a/l-unsaturated ketones, the allene often adds highly selectively to one face of the double bond.402 In the case of the ketone (489), the product (490) appeared from models to be more crowded than the alternative (491) also, the lower face of the double bond in 489 appeared to be the more hindered face. On both counts, the alternative product (491) ought to have been formed and was not. 

The fundamental reaction in catalytic olefin polymerizations is monomer insertion into an M-C bond, schematically described in Scheme 2. The general mechanistic features are well covered in two reviews.126,127... 

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