Nonconjugated dienes structure

Conjugated dienes exhibit a marked decrease in reactivity toward 9-BBN relative to alkenes and nonconjugated dienes. Structurally different double bonds, however, may allow clean monohydroboration.368 Homoallylic boranes are usually formed, but certain dienes yield allylic boranes. 

The polymerization of nonconjugated diene monomers might be expected to afford polymer chains with pendant unsaturation and ultimately, on further reaction of these groups, crosslinked insoluble polymer networks. Thus, the finding by Butler et a .,, 03, n5 that polymerizations of diallylammonium salts, of general structure 8 [e.g. diallyldimethylammonium chloride (9)] gave linear saturated polymers, was initially considered surprising. 

Di-tert-butyl- 1,3-butadiene behaves like a nonconjugated dienes because the bulky tert-butyl groups twist the structure and prevent the double bonds from lying in the same plane => the p orbitals at C2 and C3 do not overlap and delocalization (and therefore resonance) is prevented. 

Rotational isomerism normally complicates the study of gaseous nonconjugated dienes and polyenes because many conformers appear simultaneously, and hence only few structures of free molecules in this category have been studied. 

Table 3 lists all polyenes whose radical cations have been investigated by one or other of the above-described techniques and some of the structures listed are shown below the table. Note that some nonconjugated dienes do not retain their structure upon ionization [e.g. semibullvalene 104 (equation 61) or the cyclopentadiene dimers 126 and 294 (equation 62)] but break a bond to form a bisallylic radical cation, a rather common tendency of radical cations that have this possibility. 

Cyclopolymerization of Nonconjugated Dienes. Cyclopolymerization is an addition polymerization that leads to introduction of cyclic structures into the main chain of the polymer. Nonconjugated dienes are the most deeply studied monomers for cyclopolymerization and for cyclocopolymerizations with alkene monomers 66 In general, (substituted and unsubstituted) dienes with double bonds that are linked by less than two or more than four atoms cannot undergo efficient cyclization and result in crosslinked materials.12 In fact, efficient cyclopolymerization processes have been described, for instance, for a,oo-dienes like 1,5-hexadiene, 2-methyl-l,5-hexadiene, 1,6-heptadiene, and 1,7-octadiene,67 73 which lead to formation of homopolymers and copolymers containing methylene-1,3-cycloalkane units. 

Nonconjugated dienes may undergo polymerization under metathesis conditions. Metathesis, in turn, can be used for structure determination of polyalkenylenes via metathetical degradation with a low-molecular-weight olefin.6... 

With larger amount of propylene a random copolymer known as ethylene-propylene-monomer (EPM) copolymer is formed, which is a useful elastomer with easy processability and improved optical properties.208,449 Copolymerization of ethylene and propylene with a nonconjugated diene [EPDM or ethylene-propylene-diene-monomer copolymer] introduces unsaturation into the polymer structure, allowing the further improvement of physical properties by crosslinking (sulfur vulcanization) 443,450 Only three dienes are employed commercially in EPDM manufacture dicyclopentadiene, 1,4-hexadiene, and the most extensively used 5-ethylidene-2-norbomene. 

Nonconjugated dienes and polyenes have triplet photochemistry which may be considered to arise from intramolecular interaction of one excited double bond with an isolated ground-state double bond. For example, the photocyclization of enrfo-dicyclopentadiene can be effected using acetone as a sensitizer.286 Other more flexible 1,5-dienes, when sensitized to triplet states, cross couple to yield bicyclo[2.1.1]-hexane structures. For instance, triplet mercury atoms convert both 1,5-hexadiene and 1,5-cyclooctadiene to such structures.267 Irradiation of the cyclooctadiene in the presence of cuprous chloride produces the tricyclo derivative in good yield266 but recent evidence again indicates that this latter reaction may proceed via free-radical intermediates.269... 

As shown above, conjugated dienes such as 1,3-butadiene polymerize in 1,4 or 1,2 fashion depending on the catalyst and the monomer structure. Polymerization of nonconjugated dienes also results in 1,2-polymers which have pendant vinyl groups, similar to those of the conjugated dienes. 

Coordination polymerization of dienes has progressed significantly within the last decade. Selective polymerization of 1,3-dienes is reinforced by conventional transition metal catalysts and by new organolanthanide catalysts. Nonconjugated dienes also polymerize selectively to produce polymers with cyclic units or vinyl pendant groups. Living polymerization of dienes has become common, which enabled preparation of block copolymers of dienes with alkenes and other monomers. Another new topic in this field is the polymerization of allenes and methylenecycloalkanes catalyzed by late transition metal complexes. These reactive dienes and derivatives provide polymers with novel structure as well as functionalized polymers. The precision polymerization of 1,2-, 1,3-, and l,n-dienes, achieved in recent years, will be developed to construct new polymer materials with olefin functionality. 

Various other nonconjugated dienes have been used as the dieno-phile component in tandem Diels-Alder processes. In these cases, the first cycloaddition occurs as usual. Then cycloreversion with loss of COj is followed by intramolecular Diels-Alder reaction with the remaining pendant alkene to yield bicyclo[2.2.2]octene structures. For example, methyl coumalate (5-methoxycarbonyl-2-pyrone 26) reacts with 1,5-cyclooctadiene under thermal conditions to give the cage compound 27. ... 

Elastomers that fail to crystaUize on stretching must be strengthened by the addition of filters such as carbon black. SBR, poly(ethylene-ifat-propylene), and the silicone elastomers fall into this category. Whereas polyethylene is normally highly crystalline, copolymerization with propylene destroys the ordered structure and if carried out in the presence of a small quantity of nonconjugated diene (e.g., dicyclo-pentadiene), a CTOss-linking site is introduced. The material is an amorphous random... 

New types of metal-containing polymers can be effectively produced 1 construction of polymer supports in the form of gels which, in use, are capable of swelling, insoluble in the reaction medium, but permeable to the molecules, substrate and solvent (23-25). they are based on ethylene-prcpylene rubbers and also ternary copolymers of ethylene, propylene and nonconjugated diene, siloxane rubbers with the radically grafted vinylpyridine, acrylic acid (AAc), methylmethacrylate (MMA), etc. Fu2 her cross-linking of the rubber base allows the syntheses of three-dimensional networks to avoid the dispersion of these particles in the reaction media. MX is bound within these networks. Such polymers were termed mosaic their structure is shown in Fig. 2. It is evident... 

The regioselective hydroformylation of conjugated and nonconjugated dienes has been reported. One example is the low-pressure 6w-hydroformylation of 1,3-butadiene 14 to adipic aldehyde The reaction yielded adipic aldehyde with 50% selectivity over 11 other possible products. The structure of the bisphosphite ligand had the largest effect on the selectivity of this reaction. 

A molecule containing one 7t-bond as part of a C=C unit is called an alkene (see Chapter 5, Section 5.1). When a molecrde contains two 7i-bonds in two C=C units, it is called a diene. There are three fundamental structmal variations for a diene (a) those where the C=C units are separated by sp hybridized atoms, (b) those where the C=C units are connected together to form a C=C-C=C unit, and (c) those that contain two 7i-bonds that share an sp hybridized atom. Compounds (a) are called nonconjugated dienes using the standard nomenclature rules for alkenes introduced in Chapter 5, an example is 1,5-hexadiene (1). Compounds (b) are called conjugated dienes, illustrated by 1,3-hexadiene (2). Note that 2 contains an E double bond (see Chapter 9, Section 9.4.3) and the name must reflect this structural feature. Therefore, 2 is l,3 -hexadiene. 

Cyclopolymerization. As discussed earlier, nonconjugated dienes can be polymerized with metallocene-based catalysts to afford cyclopol5miers. In contrast to linear polyolefins which have only two microstructures of maximum order (isotactic and syndiotactic), cyclic polymers have four microstructures due to the possibility of configurational isomerism (cis vs trans) in the main chain (Fig. 16). Of these the frares-diisotactic structure contains no mirror planes of S5unmetry and is chiral by virtue of its main-chain stereochemistry (481). Two criteria for chirality of this microstructure are the presence of trans rings and isotacticity (the same... 

Liotta, R. Brown, H. C. 1977. Hydroboration. 48. Effect of structure on selective monohydroboration of representative nonconjugated dienes by 9-borabicyclo[ 3.3.1]nonane. J. Org. Chem. 42, 2836-2839. 

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