3.4- pentadiene units

Natta, Porri, Carbonaro and Lugli (25) have prepared copolymers of 1,3-butadiene with 1,3-pentadiene in the whole range of compositions. The properties of the copolymers, in which all butadiene and pentadiene comonomer units are in the trans-1,4 configuration, clearly show the isomorphous replacement between the two types of units. The melting point/composition data show that the copolymer melting temperatures are a regular function of composition and are always comprised between those of trans-1,4-polybutadiene modification II and trans-1,4-polypentadiene. Also the X-ray diffraction spectra of the copolymers show that the trans-1,4-pentadiene units are isomorphous with the trans-1,4-butadiene units crystallized in the crystalline modification of the latter stable at high temperatures (form II). 

The copolymerisation of butadiene and 1,3-pentadiene in the presence of V-based catalysts yields copolymers with a trans-1,4 structure of the butadiene units and a mixed trans-, M, 2 structure of the pentadiene units (in a ratio of 0.60-0.65/0.35-0.40 respectively) [61,204,205],... 

In this approach, pyrolysis gasoline first enters a C5/C6+ splitter which passes the C5 fraction to a di-cyc/o-pentadiene unit which dimerises the cyc/o-pentadiene in the C5 stream and the dimer is extracted. Excess C5 is returned to the system via an isoprene extraction unit. The mixture is then hydrogenated and olefins are saturated to paraffins. 

Trcns-1,3-pentadiene and isoprene copolymerize with Ti(On-Bu)4/ AlEta [293]. Isoprene units in the copolymer chain are predominantly of 3,4 structure while the pentadiene units are mixed of cis and trans 1,4, 1,2 and 3,4 structure composition was independent of Al/Ti ratio. Kinetic measurements were not reported but reactivity ratios (Table 26) show somewhat greater reactivity of the pentadiene and a tendency for alternation. 

The committed biosynthetic path to the leukotrienes begins (see Fig. 5.2) with the action of 5-lipoxygenase (5-LO)[EC 1.13.11.34] (14)on arachidonic acid. Purified human 5-LO is an unstable, 78,000-Da protein that has been isolated and cloned (15,16). It contains a tightly bound, nonheme iron that is essential for enzymatic activity (17). Like all known lipoxygenases, 5-LO catalyzes the insertion of molecular oxygen into a l,4-cis,cis-pentadiene unit. The effect of 5-LO on AA is to abstract stereospecifically the pro-S hydrogen at position C7 and to insert molecular oxygen at... 

The first members of an interesting new class of organometallic 7r-conjugated polymers that contain metallacyclo-pentadiene units in the main chain were reported in Double addition of acetylenes to CpCo(PPh3)2... 

Helquist and co-workers " targeted a late-stage macrolactamization of 1227 to assemble the entire carbon skeleton of madumycin 11226. Further retrosynthetic analysis focused on the final assembly of 1227, involving a 5-hydroxy-2-alkenoic acid fragment 1228, o-alanine, and an oxazole-pentadiene unit 1229 (Scheme 1.312). These authors had adapted their oxazol-2-ylzinc Reformatsky-... 

The well-known autoxidation of a Z,Z 1,4-pentadiene unit to a hydroperoxy E,Z conjugated diene is accompanied by isomerisation to... 

Molding, films, and laminating 1,4-Pentadiene United States 3,320,216 1967 Peninsular Chem Research... 

Lipoxygenase catalyzes the oxygenation of l,4-cis,a 5-pentadiene units on long-chain fatty acids to l-hydroxy-2,4-trans,cis-pentadienes. The addition of molecular oxygen involves removal of the central bisallylic hydrogen in the rate-limiting step, with the probable involvement of one iron atom on the enzyme. A possible mechanism of action is that a hydroperoxide... 

A hydrocarbon that contains two double bonds is called an alkadiene, and the rela tionship between the double bonds may be described as isolated conjugated or cumu lated Isolated diene units are those m which two carbon-carbon double bond units are separated from each other by one or more sp hybridized carbon atoms 1 4 Pentadiene and 1 5 cyclooctadiene have isolated double bonds... 

Conjugated dienes are those m which two carbon-carbon double bond units are con nected to each other by a single bond 1 3 Pentadiene and 1 3 cyclooctadiene contain conjugated double bonds... 

Chiral allenes are exanples of a small group of molecules that are chiral, but don t have a chirality center. What they do have is a chirality axis, which in the case of 2,3-pentadiene is a line passing through the three carbons of the allene unit (carbons 2, 3, and 4). 

The combination of cis-trans isomerism with iso-syndio and erythro-threo dispositions gives complex stractures as exemplified by the 1,4 polymers of 1-or 4-monosubstituted butadienes, such as 1,3-pentadiene (72, 73), and 2,4-pentadienoic acid (74, 75) and of 1,4-disubstituted butadienes, for example, sorbic acid (76). This last example is described in 32-35 (Scheme 6, rotated Fischer projection). Due to the presence of three elements of stereoisomerism for each monomer unit (two tertiary carbons and the double bond) these polymers have been classed as tritactic. Ignoring optical antipodes, eight stereoregular 1,4 structures are possible, four cis-tactic and four trans-tactic. In each series (cis, trans) we have two diisotactic and two disyndiotactic polymers characterized by the terms erythro and threo in accordance with the preceding explanation. It should be noted that here the erythro-threo relationship refers to adjacent substituents that belong to two successive monomer units. 

The trick used in asyrmnetric inclusion polymerization is to perform the reaction in a rigid and chiral environment. With more specific reference to chirality transmission, the choice between the two extreme hypotheses, influence of the starting radical (which is chiral because it comes from a PHTP molecule), or influence of the chirality of the channel (in which the monomers and the growing chain are included), was made in favor of the second by means of an experiment of block copolymerization. This reaction was conducted so as to interpose between the starting chiral radical and the chiral polypentadiene block a long nonchiral polymer block (formed of isoprene units) (352), 93. The iso-prene-pentadiene block copolymer so obtained is still optically active and the... 

Other reactions of dienes with metal atoms are only of a limited synthetic use. Dibenzylideneacetone (PhCH=CH—CO—CH=CHPh DBA) reacts with palladium vapor to afford Pd2(DBA)3, a complex in which the coordination is through the two C=C units and does not involve the C=0 (5, 92). Cobalt vapor undergoes an extremely complicated reaction with 1,4-pentadiene, producing pentenes, C5H6, and various polymers as well as the organometallic product, HCo( 1,3-pen tadiene)2, which involves isomerization from a nonconjugated to a conjugated diene (104, 110). 

The dienes, specially 1,3-pentadiene (piperylene) and hexadiene, quench the triplets of suitable sensitizers by energy transfer with unit efficiency. Hence, they are used widely in mechanistic studies of photochemical reactions, either to count the triplets or to establish the triplet energy of a sensitizer whose Et is not determinable from spectroscopic data (chemical spectroscopy). 

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