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Butadiene electrophilicity

In addition to protection, a change of diene reactivity is effected by coordination to carbonyl. Butadiene forms the very stable complex 56 and its reactions are different from those of free butadiene. Electrophiles attack C(l) or C(4) of the complexed dienes, and reactions that are impossible with uncomplexed dienes now become possible. [Pg.360]

For the simplest diene, 1,3-butadiene, electrophile attack creates an allylic cation where the greatest partial plus is on the end bearing the methyl donor group. [Pg.217]

Both resonance forms of the allylic carbocation from 1 3 cyclopentadiene are equivalent and so attack at either of the carbons that share the positive charge gives the same product 3 chlorocyclopentene This is not the case with 1 3 butadiene and so hydrogen halides add to 1 3 butadiene to give a mixture of two regioisomeric allylic halides For the case of electrophilic addition of hydrogen bromide at -80°C... [Pg.405]

When the major product of a reaction is the one that is formed at the fastest rate we say that the reaction is governed by kinetic control Most organic reactions fall into this category and the electrophilic addition of hydrogen bromide to 1 3 butadiene at low temperature is a kmetically controlled reaction... [Pg.406]

Addition Reactions. 1,3-Butadiene reacts readily via 1,2- and 1,4-free radical or electrophilic addition reactions (31) to produce 1-butene or 2-butene substituted products, respectively. [Pg.341]

Halogenation of butadiene has also attracted a lot of interest. Both 1,2- and 1,4-isomers are formed. Since the /n j -l,4-isomer was observed from the 1,4-addition product, researchers postulate that the the electrophilic forms a 1,2-cychc intermediate and not a 1,4-cychc intermediate that would form the <7j -l,4-addition product (51,52). [Pg.342]

As with addition of other electrophiles, halogenation of conjugated dienes can give 1,2- or 1,4-addition products. When molecular bromine is used as the brominating agent in chlorinated hydrocarbon solvent, the 1,4-addition product dominates by 7 1 in the case of butadiene. ... [Pg.368]

Reaction type 3 (equation 10), where the complete hetero-l,3-diene skeleton is incorporated into the newly formed ring system, occurs with compounds having both a nucleophilic center and an electrophilic center If these two functionalities are in positions 1 and 2, various types of six-membered ring systems become accessible 4,4-Bis(trifluoromethyl)-I,3-diaza-1,3-butadienes require only room temperature to react with acetyl cyanide to yield l,4,5,6-tetrahydropynmidin-6-ones [96] Likewise, certain open-chain 1,3-diketones (acetylacetone and acetoacetates) and the heterodiene form six-membered nng systems [97] (equation 19)... [Pg.848]

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. [Pg.487]

Many7 other electrophiles besides HBr add to conjugated dienes, and mixtures of products are usually formed. For example, Br2 adds to 1,3-butadiene to give a mixture of l,4-dibromo-2-butene and 3,4-dibromo-l-butene. [Pg.488]

How can we account for the formation of 1,4-addition products The answer is that allylic carbocations are involved as intermediates (recall that allylic means "next to a double bond"). When 1,3-butadiene reacts with an electrophile such as H+, two carbocation intermediates are possible a primary nonal-lylic carbocation and a secondary allylic cation. Because an allylic cation is stabilized by resonance between two forms (Section 11.5), it is more stable and forms faster than a nonallylic carbocation. [Pg.488]

Electrophilic addition to a conjugated diene at or below Toom temperature normally leads to a mixture of products in which the 1,2 adduct predominates over the 1,4 adduct. When the same reaction is carried out at higher temperatures, though, the product ratio often changes and the 1,4 adduct predominates. For example, addition of HBr to 1,3-butadiene at 0°C yields a 71 29 mixture of 1,2 and 1,4 adducts, but the same reaction carried out at 40 °C yields a 15 85 mixture. Furthermore, when the product mixture formed at 0 °C is heated to 40 °C in the presence of HBr, the ratio of adducts slowly changes from 71 29 to 15 85. Why ... [Pg.490]

The electrophilic addition of HBr to 1,3-butadiene is a good example of how a change in experimental conditions can change the product of a reaction. The concept of thermodynamic control versus kinetic control is a useful one that we can sometimes take advantage of in the laboratory. [Pg.491]

Figure 14.6 Energy diagram for the electrophilic addition of HBr to 1,3-butadiene. The 1.2 adduct is the kinetic product because it forms faster, but the 1,4 adduct is the thermodynamic product because it is more stable. Figure 14.6 Energy diagram for the electrophilic addition of HBr to 1,3-butadiene. The 1.2 adduct is the kinetic product because it forms faster, but the 1,4 adduct is the thermodynamic product because it is more stable.
Electrophilic addition of Br2 to isoprene (2-methyl-l,3-butadiene) yields the following product mixture ... [Pg.510]

In the case of electrophiles like Br", which can form cyclic intermediates, both 1,2-and 1,4-addition products can be rationalized as stemming from an intermediate like 17. Direct nucleophilic attack by W would give the 1,2 product, while the 1,4 product could be formed by attack at the 4 position, by an Sn2 type mechanism (see p. 422). Intermediates like 18 have been postulated but ruled out for Br and Cl by the observation that chlorination or bromination of butadiene gives trans 1,4... [Pg.980]

Random copolymerization occnrs between butadiene and styrene [15]. There are no appreciable differences in the nncleophilic and electrophilic abilities between the radical centers with the vinyl and phenyl groups at the end of the growing polymer chain or in the donor/acceptor properties between the monomers. [Pg.20]

The isothiocyanate (21) reacted with dienes to give the phosphoranes (22) more rapidly than did the corresponding fluoride and chloride, but less rapidly than did the bromide. The rates of reactions of (21) with various dienes were in the order isoprene > butadiene > piperylene > chloroprene. These data support the previous suggestion that attack on the diene is an electrophilic process. [Pg.34]

Nickel(O) complexes are extremely effective for the dimerization and oligomerization of conjugated dienes [8,9]. Two molecules of 1,3-butadiene readily undergo oxidative cyclization with a Ni(0) metal to form bis-allylnickel species. Palladium(O) complexes also form bis-allylpalladium species of structural similarity (Scheme 2). The bis-allylpalladium complexes show amphiphilic reactivity and serve as an allyl cation equivalent in the presence of appropriate nucleophiles, and also serve as an allyl anion equivalent in the presence of appropriate electrophiles. Characteristically, the bis-allylnickel species is known to date only as a nucleophile toward carbonyl compounds (Eq. 1) [10,11],... [Pg.183]

Butadiene shows 1,4-addition reactions with electrophilic reagents other than HC1. [Pg.518]

The reaction of phenylhydrazones with butadiene was carried out by Baker on the basis of the idea that phenylhydrazones have both nucleophilic nitrogen and electrophilic carbon. Products 77-79 were obtained by the reaction of phenylhydrazones with Pd(PPh3)4 (81) ... [Pg.167]

A study of the reactions of butadiene, isoprene, or allene coordinated to nickel in a metallacycle, with carbonylic compounds, has been reported by Baker (example 11, Table IV). In the presence of phosphines, these metallacycles adopt a cr-allyl structure on one end and a ir-allyl structure on the other, as mentioned in Section II,A,1. The former is mainly attacked by aldehydes or electrophilic reagents in general, the latter by nucleophiles (C—H acids, see Table I, or amines, see Table IX). [Pg.221]

Absolute rates for the addition of the methyl radical and the trifluoromethyl radical to dienes and a number of smaller alkenes have been collected by Tedder (Table l)3. Comparison of the rate data for the apolai4 methyl radical and the electrophilic trifluoromethyl radical clearly show the electron-rich nature of butadiene in comparison to ethylene or propene. This is also borne out by several studies, in which relative rates have been determined for the reaction of small alkyl radicals with alkenes. An extensive list of relative rates for the reaction of the trifluoromethyl radical has been measured by Pearson and Szwarc5,6. Relative rates have been obtained in these studies by competition with hydrogen... [Pg.620]

As a point of reference, relative rates for methyl methacrylate have also been included in Table 6. While addition to butadiene or isoprene is significantly faster as compared to methyl methacrylate for electrophilic or ambident radicals, little rate variation is found for the 1-phenylethyl radical. [Pg.624]

Compared with the anodic oxidation of a 1,3-diene, the cathodic reduction of a 1,3-diene may be less interesting since the resulting simple transformation to monoolefin and alkane is more conveniently achieved by a chemical method than by the electrochemical method. So far, only few reactions which are synthetically interesting have been studied15. The typical pattern of the reaction is the formation of an anion radical from 1,3-diene followed by its reaction with two molecules of electrophile as exemplified by the formation of the dicarboxylic acid from butadiene (equation 22)16. [Pg.768]

In this process the primary step is the formation of an anion, which is a synonym for a nucleophile, mostly by deprotonation using a base. It follows a reaction with an electrophile to give a new anion which in the anionic-anionic process again reacts with an electrophile The reaction is then completed either by addition of another electrophile as a proton or by elimination of an X group. Besides the anionic-anionic process there are several examples of anionic-pericydic domino reactions as the domino-Knoevenagel-hetero-Diels-Alder reaction in which after the first step an 1-oxa-l,3-butadiene is formed. [Pg.45]

Addition reactions, 20 243. See also Electrophilic addition reactions aldehydes, 2 63-64 allyl alcohol, 2 234-239 butadiene, 4 368—370 carboxylic acids, 5 44-45 ethylene, 10 597—598 quinoline, 21 184 quinone, 21 246-261 toluene, 25 165... [Pg.15]

Diels-Alder adduct from cyclopentadiene, 8 222t Diels-Alder reactions of, 25 488-489 economic aspects of, 25 507-509 electrophilic addition of, 25 490 in ene reactions, 25 490 esterification of, 25 491 free-radical reactions of, 25 491 from butadiene, 4 371 Grignard-type reactions of, 25 491 halogenation of, 15 491—492 health and safety factors related to, 25 510-511... [Pg.546]


See other pages where Butadiene electrophilicity is mentioned: [Pg.438]    [Pg.407]    [Pg.465]    [Pg.37]    [Pg.793]    [Pg.407]    [Pg.306]    [Pg.491]    [Pg.102]    [Pg.328]    [Pg.111]    [Pg.80]    [Pg.217]    [Pg.156]    [Pg.194]    [Pg.109]    [Pg.167]    [Pg.621]    [Pg.907]   
See also in sourсe #XX -- [ Pg.134 ]




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1.3-Butadiene electrophilic addition

Substitutions electrophilic, - 1,3-butadiene

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