Addition to a Double Bond

Reversing the order of addition, or using an ether as a solvent, causes a marked retardation of the reaction, with subsequent sudden, uncontrollable speed-up. Yields of about 80% are obtained and probably can be unproved b devices to minimize the mechanical losses.  

The addition of hydrogen fluoride to stearolic acid in methylene chloride solution to give 9,10-difluorostearic acid is cited in the patent literature. This claim should be verified, as either 9,9- or 10,10-difluoro-steaiic acid or a mixture is much more likely to be the reaction product. 

When hydrogen fluoride adds to an olefin, the fluorine becomes attached to the carbon with the least hydrogen. Ethylene yields ethyl fluoride propylene yields isopropyl fluorine cyclohexene gives cyclohexyl fluoride. Cyclopropane yields n-propyl fluoride when the reaction is conducted very slowly at 0°, but if the temperature is not well regulated an isomerization takes place to yield isopropyl fluoride. The reactions are all non-cataljrtic and take place in paraffin or metal containers equally well. The yields are from 60 to 80%.  

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Electrophilic addition (Section 11 16) An aryl group stabilizes a benzylic carbocation and con trols the regioselectivity of addition to a double bond involving the benzylic carbon Markovni kov s rule is obeyed... 

Conjugated dienes also undergo electrophilic addition reactions readily, but mixtures of products are invariably obtained. Addition of HBr to 1,3-butadiene, for instance, yields a mixture of two products (not counting cis-trans isomers). 3-Bromo-l-butene is the typical Markovnikov product of 1,2-addition to a double bond, but l-bromo-2-butene appears unusual. The double bond in this product has moved to a position between carbons 2 and 3, and HBr has added to carbons 1 and 4, a result described as 1,4-addition. 

The adducts containing di- and tribromomethyl groups can react with another molecule of monomer, i.e. the secondary reactions occur including step-by-step telomerization in this case. The presence of the bromine atom adjacent to the radical center makes it probable the fragmentation with ejection of the bromine atom, which starts the further reaction, and as a result, the products of bromine addition to a double bond, not adducts, are formed. 

In investigating the mechanism of addition to a double bond, perhaps the most useful type of information is the stereochemistry of the reaction. The two carbons of the double bond and the four atoms immediately attached to them are all in a plane (p. 8) there are thus three possibilities. Both Y and W may enter from the same side of the plane, in which case the addition is stereospecific and syn they may enter from opposite sides for stereospecific anti addition or the reaction may be nonstereospecific. In order to determine which of these possibilities is occurring in a given reaction, the following type of experiment is often done YW is added to the cis and trans isomers of an alkene of the form ABC=CBA. We may use the cis alkene as an example. If the addition is syn, the product will be the erythro dl pair, because each carbon has a 50% chance of being attacked by Y ... 

Peroxyl radicals can undergo various reactions, e.g., hydrogen abstraction, isomerization, decay, and addition to a double bond. Chain propagation in oxidized aliphatic, alkyl-aromatic, alicyclic hydrocarbons, and olefins with weak C—H bonds near the double bond proceeds according to the following reaction as a limiting step of the chain process [2 15] ... 

The C-H bond activation followed by addition to a double bond leads to the formation of alkylated compounds (Equation (1)). This reaction involves aromatic, aliphatic, olefinic, and acetylenic C-H bonds. 

The addition to a double bond is observed in aromatic substrates where the reaction is assisted by chelation. The initial success of such reactions was achieved with the double alkylation of phenol with ethene (Equation (2)).1 This reaction occurs at the or/ -positions selectively by using an orthometallated ruthenium phosphate complex 1. 

The NMR spectra of C qHR exhibits 37 resonances of the fuUerene carbons, with two of them in the sp region, proving Q-symmetry for the C oHR adducts. This is consistent with an addition to a double bond of a pole corannulene imit (1,2-addition), leading to l,2-dihydro[70]fullerene derivatives. These particular [6,6] bonds of Cyg, located between the carbons of the sets A and B, have almost the same bond length as the [6,6] bonds in Cjq [30], and the pole corannulene unit also exhibits bond alternation with longer [5,6] bonds. NMR data imply that the initial attack of the nucleophile occurred on C-1 and the protonation on C-2. 

When irradiating a neon-chlorine mixture chlorine, mono[ F]fluoride (CI[ F]F) of high specific activity can be obtained [45], In electrophilic reactions this reagent would rather introduce the less-electronegative non-radioactive chlorine atom. However, addition to a double bond should be feasible as has been shown for bromine [ F]fluoride (Brp F]F) prepared more recently from activated [ F]fluoride [64-66],... 

Irradiation of a mixture of neon and nitric oxide gives no-carrier-added nitrosyl [ F]fluoride (ON[ F]F) [45,67], Hydrolysis yields [ F]fluoride that was proposed for bone scanning. ON[ F]F was designed with steroid labelling in mind in which addition to a double bond should lead to an a-[ F]fluoroketone entity, but this idea was not further pursued. 

The reaction proceeds primarily by addition to a double bond to form a chlorine-containing alkyl radical, which then adds 02 to ultimately generate characteristic chlorine-containing oxygenated products. For example, l-chloro-3-methyl-3-buten-2-one is formed in the absence of NO from the addition of chlorine atoms to the 4-position of isoprene, followed by secondary reactions of the alkyl radical with 02 etc. This product might therefore be expected to be a reaction product in the low-NOj. environment of the marine boundary layer (Nordmeyer et al., 1997). 

These reactions are fast for a-hydrogens to -OH, -OR, or -NH2 substituents and considerably slower for a-hydrogens to -C02 and -NH,[ substituents (7). A small part of the primary radicals react with hydrogens at the (3-position. OH/ H radicals react very fast with aliphatic unsaturated compounds and aromatic compounds via addition to a double bond ... 

HO reacts with organic pollutants primarily in two different ways (i) by electrophilic addition to a double bond or an aromatic system (Eq. 16-12), and (ii) by abstraction of a hydrogen atom from a carbon atom (Eq. 16-13) ... 

The following reactions correspond to typical additions to a double bond being part of a heterocyclic molecule. 

Only a few examples are known in which an enzyme induces addition to a double bond that is not conjugated with a carbonyl or carboxyl group. Pseudomonads have been observed to catalyze stereospecific hydration of oleic acid to D-10-hydroxystearate.96 The addition is anti and the proton enters from the re face. 

An interesting use is made of addition to a double bond by glutathione-dependent cis-tmns isomerases.76 One of them converts maleate to fumarate with a turnover number of 300 s"1. Similar enzymes, which participate in bacterial breakdown of aromatic compounds (Fig. 25-7), isomerize maleylacetoacetate and maleylpyruvate to the corresponding fumaryl derivatives (Eq. 13-20). The - SH group of bound glutathione is thought to add to the double bond. Rotation can then occur in the enolic intermediate. Thiocyanate ion catalyzes the isomerization of maleic acid nonenzy-matically, presumably by a similar mechanism. 

Reduction of the parent systems is of little importance as reduced forms of 1,4-oxazines and -thiazines are readily available by other means moreover, hydrogenation of thiazines may effect cleavage and ring contraction to thiazolines rather than straightforward addition to a double bond as was once supposed (Scheme 39) (68G17). 

HC1, involves partial oxidation of the methane. Also, when a halogen addition to a double bond is made, this is regarded as an oxidation. 

The opposite of an addition to a double bond is a 1,2-elimination reaction. In solution, where the reaction is promoted by solvent or by base, the most common eliminations (and those to which we shall limit our discussion) are those that involve loss of HX, although loss of X2 from 1,2-dihalides and similar reactions are also well known. The mechanisms of eliminations of HX are of three main types (1) The Ex (elimination, first-order), shown in Equation 7.22, which is the reverse of the AdE2 reaction and which has the same first, and rate-determining,... 

In a synthesis of hemibrevetoxin B, electrophilic addition to a double bond (Equation 23) was successfully used to... 

Peroxy radicals(R02) react with organic compounds either by H-atom transfer or addition to a double bond. These reactions have rate constants ranging from <0.01 to 300 M 1 s 1 at 25°C (Howard, 1972 Hendry et al., 1974 Neta et al., 1990) and are rarely important under environmental conditions because of the low average concentration of R02 in surface waters (Table 15.5). However, H-atom transfers from phenol OH or aniline NH have large... 

Finally, halogens can be introduced by electrophilic addition to a double bond (Scheme 3.4b). For example, the reaction of glucal with xenon difluoride in the presence of a catalytic amount of BF3 OEt2 gives a 2-deoxy-2-fluoro-glucosyl fluoride as a mixture of anomers.19... 

Therefore, in aqueous N20 saturated solutions, OH radicals are the predominant species (90%), while in acidic aqueous solution H and OH radicals exist, but not hydrated electrons. The small fraction ( ca 10%) of hydrogen atoms in N20 saturated aqueous solution does not interfere significantly with the measurements of the reactions of OH radicals. Frequently, H atoms and OH radicals react with solutes in a similar manner, e.g. by addition to a double bond or by hydrogen atom abstraction, however with different rate constants. 

As the active metal-carbon bond assumes more covalent character, there will be a greater tendency for hemolytic cleavage and radical-type polymerizations. This becomes favorable when the alkyl is attached to a transition metal in one of its highest valence states or to a non-transition metal of Group IV or V. One can expect such catalysts to initiate polymerizations by both the conventional simple free radical and coordinated radical mechanisms. Stereospecificity generally suffers in these systems because both mechanisms are operative and because radical addition to a double bond is less selective for producing a head-to-tail polymer structure. 

The addition of a triplet carbene to an aikene can be considered to be rather like a radical addition to a double bond. The concerted addition of a singlet carbene, on the other hand, is a pericyclic reaction, and from Chapter 35 you should be able to classify it as a [ 1 + 2] cycloaddition. 

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