Addition-elimination summary

It is well known that not all attempts to explain the reactivity of individual positions in electrophilic substitution reactions have been successful. There are three main lines along which attempts have been made to remove discrepancies between theory and experiment (for a summary, see ref. 147) (1) introduction into the HMO treatment of additional empirical parameters (inductive effect), (2) invoking the addition-elimination mechanism, and (3) invoking different reactivity of the protonated and unprotonated forms. 

In summary, aryl halides can undergo substitution by addition-elimination, SrnI, or elimination-addition mechanisms under basic conditions. The addition-elimination mechanism is most reasonable when the arene is electron-poor. When the arene is not electron-poor, the SrnI mechanism is most reasonable either when the nucleophile is a heavy atom or is delocalized, when light is required, or when a catalytic amount of a one-electron reducing agent is required. The elimination-addition mechanism is most reasonable when the arene is not electron-poor and when very strong base (pk b > 35) is used. 

Atom Variations E2 Heteroatom Variants, Dehalogenation, Fragmentation Vinylogous Variations Sn2 and E2. 1,4 additions Extent of Proton Transfer Variations General Acid and General Base Catalysis of Additions and Eliminations, Summary by Media, Push-Pull Catalysis of Enolization... 

Addition-Elimination of Carboxylic Acid Derivatives Summary... 

There are two general classes of reactions to change coordination at a reaction center addition/elimination and substitution. The words used to identify and further characterize these reactions are traditionally different in organic and in inorganic chemistry. In order to have a common basis for discussing analogous processes at such diverse reaction centers as Cd, Pb, Sn, Ge, Si, C, Al, and B, we start by giving a condensed summary of the respective classifications. 

The reactions of carboxylic acids and their derivatives are summarized here. Many (but not all) of the reactions in this summary are acyl substitution reactions (they are principally the reactions referenced to Sections 17.5 and beyond). As you use this summary, you will find it helpful to also review Section 17.4, which presents the general nucleophilic addition-elimination mechanism for acyl substitution. It is instructive to relate aspects of the specific acyl substitution reactions below to this general mechanism. In some cases proton transfer steps are also involved, such as to make a leaving group more suitable by prior protonation or to transfer a proton to a stronger base at some point in a reaction, but in all acyl substitution the essential nucleophilic addition-elimination steps are identifiable. 

In summary, photochemical methods exploit the high energy of the adsorbed photon in various ways - that is, either via reaction of the electronically excited state itself, whether involving the usual addition-elimination mechanism of arenes or unimolecular fragmentations, or via electron transfer followed by fragmentation of one of the charged radical ions. 

Summary Carbonyl compounds readily undergo addition-elimination reactions ... 

Several examples of such processes have been noted in Section III and include transhalogenation to the very stable a-metallated compounds 678 or 679, ring opening, and stepwise elimination to nonaryne intermediates which can rearrange or attack the aryne traps which are present. The lower resonance energy of five-membered heterocycles compared to benzenoid compounds makes them much more susceptible to addition reactions, and hence both cine-substitution and Diels-Alder products have been shown to sometimes arise by addition-elimination and not elimination-addition mechanisms. A summary of all the demonstrated nonaryne reactions of five-membered hetaryne precursors discussed in Section III is collected in Table 8. 

Nucleophilic Aromatic Substitution 490 The Addition-Elimination Mechanism of Nucleophilic Aromatic Substitution 492 Related Nucleophilic Aromatic Substitutions 494 12.22 Summary 496 Problems 500... 

Carboxylic acids and carboxylic acid derivatives can also be prepared by methods other than nucleophilic addition-elimination reactions. A summary of the methods used to synthesize these compounds is provided in the Study Area of MasteringChemistry. 

In Summary Nucleophilic attack on the carbonyl group of carboxylic acid derivatives is a key step in substitution by addition-elimination. Either acid or base catalysis may be observed. For carboxylic acids, the process is complicated by the poor leaving group (hydroxide) and competitive deprotonation of the acid by the nucleophile, acting as a base. With less basic nucleophiles, addition can occur. 

In Summary Amines react with carboxylic acids to form amides by an addition-elimination process that begins with nucleophilic attack by the amine on the carboxy carbon. Amide formation is complicated by reversible deprotonation of the carboxylic acid by the basic amine to give an ammonium salt. 

In Summary The relative electronegativity and the size of L in RCL controls the extent of resonance of the lone electron pair(s) and the relative reactivity of a carboxylic acid derivative in nucleophilic addition-elimination reactions. This effect manifests itself structurally and spectroscopically, as well as in the relative acidity and basicity of the a-hydrogen and the carbonyl oxygen, respectively. 

In Summary Acyl chlorides are attacked by a variety of nucleophiles, the reactions leading to new carboxylic acid derivatives, ketones, and aldehydes by addition-elimination mechanisms. The reactivity of acyl halides makes them useful synthetic relay points on the way... 

A variety of mechanisms have been show to operate in alkenylation of nucleophiles including ligand coupling, addition-elimination and elimination-addition reactions for anionic nucleophiles and vinylic Sjv2, vinylic Sjvl and elimination-addition reactions for neutral nucleophiles. The mechanisms so far elucidated have been extensively reviewed by Ochiai and Okuyama and herein we provide a summary of these processes. 

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

In summary, a polymer is classified as a condensation polymer if its synthesis involves the elimination of small molecules, or it contains functional groups as part of the polymer chain, or its repeating unit lacks certain atoms that are present in the (hypothetical) monomer to which it can be degraded. If a polymer does not fulfill any of these requirements, it is classified as an addition polymer. 

The hydroxyl content of the lignin was incrementally eliminated by acetylation and ethylation according to previously described procedures (11). In addition, modification with propylene oxide was also used to alter the original lignin structure (12). Table I presents a summary of the hydroxy content, and pertinent physical properties, of the derivatized lignins. 

A capsule summary of the merits of the three kinds of corrective action can be made. The proportional action is rapid but has a permanent offset that increases as the action speeds up. The addition of integral action reduces or entirely eliminates the offset but has a more sluggish response. The further addition of derivative action speeds up the correction. The action of a three-mode PID controller can be made rapid and without offset. These effects are illustrated in Figure 3.3 for a process subjected to a unit step upset, in this case a change in the pressure of the control air. The ordinate is the ratio of the displacements of the response and upset from the set point. 

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