Typical Addition Reactions of

As mentioned previously, although the benzene ring is unsaturated it is generally very stable and does not give the typical addition reactions of unsaturated compounds. Its reactions are generally substitution reactions. 

Addition pdlymeiization is characterised by the fact that the reaction from monomer to polymer occurs without elimination of by-products. During the addition reaction, no stable compoimds are formed because the intermediates are comparatively short-lived radicals or ions. The formation of the polymer chain is usually accomplished in a fraction of a second and in one angle sweep. Polymerization at the double bond is a typical addition reaction of this type. Certain addition reactions, which proceed by first opening the ring of a cyclic compound, follow a stepwise procedure. Thus they occupy a position in between the two reaction types, showing certain dmilarities to each. 

The negative signs for both AH° and AS " in typical addition reactions of alkenes cause the competition between addition and elimination to be strongly temperature-dependent. Addition is favored at low temperatures, elimination at high temperatures. The economically important hydrogenation-dehydrogenation equilibrium that connects ethylene and ethane illustrates this. 

Applied to benzene the residual affinities were expressed as in (VIII) and it was suggested that the neutralisation of the partial valencies all around the ring led to their lack of reactivity in typical addition reactions of alkenes. 

Despite its molecular formula, benzene for the most part does not behave as if it were unsaturated. For instance, it does not decolorize bromine solutions the way alk-enes and alkynes do (Sec. 3.7a), nor is it easily oxidized by potassium permanganate (Sec. 3.17a). It does not undergo the typical addition reactions of alkenes or alkynes. Instead, benzene reacts mainly by substitution. For example, when treated with bromine (Br2) in the presence of ferric bromide as a catalyst, benzene gives bromobenzene and hydrogen bromide as products. 

Conjugate addition reactions of acyclic Midiael acceptors possessing betetoatom-SLibstituted stereogenic centers in tlieir )>-positions may provide usefiil levels of diastereoselectivity. A typical example is given witli tlie y-alkoxy-substituted enoate 49 in Sdieme 6.8 [17]. High levels of diastereoselectivity in favor of tlie anii addition product SO were found in tlie course of dlmediylcuprate addition. 

Let s look at a typical polar process—the addition reaction of an alkene, such as ethylene, with hydrogen bromide. When ethylene is treated with HBr at room temperature, bromoethane is produced. Overall, the reaction can be formulated as... 

Benzene shows neither the typical reactivity nor the usual addition reaction of ethylene. Benzene does react with bromine, Brs, but in a different type of reaction ... 

The addition reaction of alkenes and phenylmercuric bromide typically occurs at about 80°C. Phenylmercuric iodides are somewhat more reactive and may be advantageous in reactions with relatively unstable alkenes.167... 

The solid-state polymerization of diacetylenes is an example of a lattice-controlled solid-state reaction. Polydiacetylenes are synthesized via a 1,4-addition reaction of monomer crystals of the form R-C=C-CeC-R. The polymer backbone has a planar, fully conjugated structure. The electronic structure is essentially one dimensional with a lowest-energy optical transition of typically 16 000 cm-l. The polydiacetylenes are unique among organic polymers in that they may be obtained as large-dimension single crystals. 

In this context, an avalanche of studies were devoted to acid-base reactions in their broadest sense (i.e., the Lewis picture), also involving complexation reactions, to the typical organic reactions of addition, substitution, and elimination types, involving nucleophilic and electrophilic reagents including the case of radicalar reactions and excited states (for a review see Ref. [11]) in which our group has... 

The addition reactions of aryl azides onto enamines bearing a carbonyl, sulfonyl, or nitro group in the 0 position with respect to the nitrogen atom have been investigated by Italian authors.240-241 The expected triazoline derivatives could not be isolated but were immediately converted into the corresponding 1,2,3-triazoles (49) and secondary amines. The reaction of p-nitrophenyl azide with l-benzoyl-2-morpholino-l-propene (48) is given as a typical example. 

Hydrosilylations of fluorine-containing alkenes are free radical reactions initiated by UV light or organic peroxides The direction of addition is the same as with fluonnated alkyl halides However, the reaction between hydrosilanes and fluorine-containing olefins catalyzed by platinum group metal complexes may result in bidirectional addition and/or formation of a vinylic silane, the latter by de hydrogenative silylation[/] The natures of both the silane and the catalyst affect the outcome of the reaction[7] A random selection of some typical new reactions of silanes are shown in Table 1 [1, 2, 3 4]... 

The carbonylchloroiridium(III) porphyrins can be transformed into a variety of other carbonyl complexes by chloride exchange with acids or salts (path e). Concentrated sodium hydroxide in ethanol appears to destroy the carbonyl ligand in these compounds (path — d, a) in a manner similar to the alkoxide addition to RhCl(TPP) CO (path f) here, this should give a carboxylic acid RhCOOH(P) which is decarboxylated to a hydride RhH(P) according to the typical base reaction of metal carbonyls. The hydride may then be autoxidized to the hydroxide. 

An example of a typical addition reaction with an organic solute is that of benzene, shown in Eq. (5). The aromaticity of benzene is destroyed, opening the way for ring-opening reactions. 

Addition reactions with Mode A are popular, and most addition reactions are classified into this group. The most typical experimental procedure is the treatment of alkyl halides (RBr, RI) and electron-deficient olefins with Bu3SnH in the presence of AIBN. Bu3GeH or Ph3GeH can be also used instead of Bu3SnH however, there are rather expensive and less reactive. Typical addition reactions are shown below, in... 

Metal complexes of heterocyclic compounds display reactivities changed greatly from those of the uncomplexed parent systems. All of the -electron system(s) of the parent heterocycle can be tied up in the complex formation, or part can be left to take part in alkenic reactions. The system may be greatly stabilized in the complex, so that reactions, on a heteroatom, for example, can be performed which the parent compound itself would not survive. Orbital energy levels may be split and symmetries changed, allowing hitherto forbidden reactions to occur. In short, a multitude of new reaction modes can be made possible by using complexes dimerization of azirines with a palladium catalyst serves as a typical example (Scheme 81). A variety of other insertion reactions, dimerizations, intramolecular cyclizations, and intermolecular addition reactions of azirines are promoted by transition metals. 

This mechanism qualitatively accounts for all products except the Cn.iH2n-2 and Cn.2H2n.4 olefins. These olefins cannot be formed from a CnH2n.r parent radical by any reasonable bond cleavage an alternate pathway also must be available. The most likely possibility is that these olefins come from heavier (than CMH2n.r) parent radicals formed by the addition of chain carriers to the reactant olefins, followed by decomposition. The presence of small amounts of Crt+iH2n+2 and Cn+2H2n+4 olefins as primary products supports this hypothesis. Typical addition reactions follow. 

In Step [3], OH adds to the carbonyl group in a typical nucleophilic addition reaction of a ketone, but the three I atoms give this ketone a good leaving group, Xla. 

---