Units olefinic

Olefin fibers, also called polyolefin fibers, are defined as manufactured fibers in which the fiber-forming substance is a synthetic polymer of at least 85 wt % ethylene, propjiene, or other olefin units (1). Several olefin polymers are capable of forming fibers, but only polypropylene [9003-07-0] (PP) and, to a much lesser extent, polyethylene [9002-88-4] (PE) are of practical importance. Olefin polymers are hydrophobic and resistant to most solvents. These properties impart resistance to staining, but cause the polymers to be essentially undyeable in an unmodified form. 

X-ray crystal stmcture analysis of 10 and 11 has revealed a close contact between Fe and the Li ion of ca. 2.5 A. Moreover, the Li ion resides close to the olefin units. Stabilization of the electron-rich Fe center by the 7t-accepting character of the olefins is evidenced by the significant elongation of the C=C bonds to ca. 

Alternating isoprene-ethylene copolymers (IER) were prepared with the same catalyst. Due to the strictly alternating sequences of diene and olefin units and the absence of chiral carbon atoms IER shows strain-induced crystallization, but at lower temperatures compared to natural rubber. 

Titanium-mediated intramolecular Friedel-Crafts acylation and alkylation are important methods for construction of fused-ring systems (Scheme 29).107 As well as aromatics, olefin units also react in the same way.108 Alkylation of electron-rich olefins such as enol ethers or silyl enol ethers proceeds effectively in the presence of TiCl4.109... 

Recently, a metallocene/MAO system has been used for the polymerization of non-conjugated dienes [204, 205]. The cyclopolymerization of 1,5-hexadiene has been catalyzed by Zieger-Natta catalyst systems, but with low activity and incomplete cyclization in the formation 5-membered rings [206]. The cyclopolymerization of 1,5-hexadiene in the presence of ZrMe2Cp2/MAO afforded a polymer (Mw = 2.7 x 107, Mw/Mn = 2.2) whose NMR indicated that almost complete cyclization had taken place. One of the olefin units of 1,5-hexadiene is initially inserted into an M-C bond and then cyclization proceeds by further... 

The product of the dimerization of an unsymmetrical substituted olefin, such as propene, is dependent on the direction of coupling of the two olefinic units in general, a mixture of isomers is obtained. In order to obtain a high yield of a particular dimer, the control of the regioselectivity of the individual addition steps in the catalytic cycle or even the reversal of the direction of addition in consecutive steps is required (Section IV,E). 

The configuration of the product in diastereoselective hydrogenation -whether 1,2-syn or 1,2-anti - is related to the substitution pattern of the starting alkene. The allyl alcohol with a 1,1-disubstituted olefin unit affords the antiproduct, while the syn-product is formed from the allyl alcohol with a trisubsti-tuted olefmic bond (Table 21.8, entries 6-9). The complementarity in diastereoselective hydrogenation of di- and tri-substituted olefins may be rationalized based on the conformation analysis of the intermediary complex (Scheme 21.1)... 

In entries 10-13 (Table 21.8) of trisubstituted alkenes, very high diastereo-selectivity is realized by the use of a cationic rhodium catalyst under high hydrogen pressure, and the 1,3-syn- or 1,3-anti-configuration naturally corresponds to the ( )- or (Z)-geometry of the trisubstituted olefin unit [48, 49]. The facial selectivity is rationalized to be controlled by the A(l,3)-allylic strain at the intermediary complex stage (Scheme 21.2) [48]. 

In the case of tri-substituted alkenes, the 1,3-syn products are formed in moderate to high diastereoselectivities (Table 21.10, entries 6—12). The stereochemistry of hydrogenation of homoallylic alcohols with a trisubstituted olefin unit is governed by the stereochemistry of the homoallylic hydroxy group, the stereogenic center at the allyl position, and the geometry of the double bond (Scheme 21.4). In entries 8 to 10 of Table 21.10, the product of 1,3-syn structure is formed in more than 90% d.e. with a cationic rhodium catalyst. The stereochemistry of the products in entries 10 to 12 shows that it is the stereogenic center at the allylic position which dictates the sense of asymmetric induction... 

Reactor systems that can be described by a yield matrix are potential candidates for the application of linear programming. In these situations, each reactant is known to produce a certain distribution of products. When multiple reactants are employed, it is desirable to optimize the amounts of each reactant so that the products satisfy flow and demand constraints. Linear programming has become widely adopted in scheduling production in olefin units and catalytic crackers. In this example, we illustrate the use of linear programming to optimize the operation of a thermal cracker sketched in Figure E 14.1. 

Dehydroarachidonic acid analogs in which one Z-olefinic unit is replaced by a triple bond are irreversible inhibitors of the lipoxygenasses which normally deliver dioxygen to the corresponding site of arachidonic acid. The inactivation appears to be a consequence of dioxygenation at the acetylinic unit to from a vinyl hydroperoxide which undergoes rapid 0-0 homolysis. Synthetic routes to these interesting enzyme inhibitors are outlined below. 

In the case of the Pd-bis-imine catalyst the isomerization process has a barrier of 5.8 kcai/mol [13c] for the generic system and 6.1 kcal/mol [16] for the real catalyst. The lower barrier is a result of the longer Pd-N distance (compared to the Ni-N bond length) which provides space for rotation of the olefin unit, even when the bis-imine nitrogens are attached to bulky substituents. 

The presence of the large cyclic olefin units randomly distributed in the backbone leads to an amorphous copolymer combining high transparency, low birefringence, stiffness, barrier properties and the general characteristics of olefins. 

The reductive cyclization of readily available enol phosphates of 1,3-dicarbonyl compounds bearing pendant olefinic units has been explored [66,67]. The chemistry is exceptionally interesting, and provides a unique route to structures possessing a cyclopropyl unit which is suitable for structural elaboration. The reaction occurs in a manner wherein the phosphate-bearing carbon behaves like a carbene that adds to the pendant alkene to form a cyclopropane. While this provides a useful way of viewing the transformation, mechanistic studies indicate that a carbene is not an actual intermediate. Examples are portrayed in Table 11. 

Before the incident, the facility had experienced a power failure that led to the shutdown of an olefins unit. For several hours, a restart had been attempted and the compressor had tripped on high vibration at low speed. This caused the check valve to close, which placed additional stresses on the valve shaft. Failure to execute a smooth planned start-up was a key contributor to the timing of this incident. However, given the design defects inherent in the valve, an ultimate failure was inevitable. 

Examination of the C-NMR spectra of roseadine (23) (Table XI) through comparison with vindoline (3) and leurosine (11) permitted the assignment of all carbons of the dihydroindole unit. The carbons of the indole nucleus were assigned by comparison with vinblastine (1), and the presence of three deshielded carbons, a methine carbon at 8 142.9 and two quaternary carbons at 8 133.2 and 169.2, were observed. The latter was assigned to the methoxycarbonyl carbon, which is shielded somewhat from its characteristic chemical shift of 8 174 1 ppm in the vinblastine series by attachment of an olefinic unit. The other two deshielded carbons at 8 133.2 and 142.9 could be assigned as C-18 and C-17, respec-... 

The two most used reversible covalent reactions are disulfide exchange and palladium-catalyzed olefin metathesis. We first probed the incorporation of olefin units into the H bonded duplexes by subjecting the modified duplexes to a Pd (Gmbb s) catalyst. Based on a duplex template with the same unsymmetrical H bonding sequence used for directing the formation of the /3-sheet structures, we prepared two groups (strands 17 and 18) of five olefins covalently linked to the two template strands (Fig. 9.13). Mixing each one of components 17 with each one of components 18 in a 1 1 fashion results in a small library of 25 (5 x 5) members. 

The experimental autoclave results are summarized in Table I and Figures 2 through 4. Autoclave product compositions are expressed in weight percent, assuming that one peroxide function per olefin unit is incorporated in the polymeric dialkyl peroxides (17, 19). 

Methylene cyclohexenes are other products obtained by cyclopropanation of the carbene gold intermediate over a second olefin unit [148]. 

Butadiene. Most butadiene [106-99-0] is produced by extraction of C4 streams from olefins units. Only about one-third of butadiene was... 

A manufactured fiber in which the hbeplorming substance is any long-chain synthetic polymer composed of at least 85% by weight of ethylene, propylene, or other olefin units, A porlion of Lhe molecule may appear as ... 

Lewis acid catalyzed intramolecular coupling of allylsilanes with aziridines serves as a useful route for the synthesis of carbocycles having the y-amino olefin unit 104 (equation 80)149. However, this reaction does not occur in an intermolecular manner. 

The following aspects will be addressed. (1) Conjugated polymers with benzene-derived repeat units (section II) typical examples are the already mentioned poly-/>phenylene (PPP) 6,43 polyphenylene-vinylenes (PPV) 9,43 and polyphenyleneethinylenes (PPE) 25.44 Some typical questions are obvious how do the aromatic or olefinic units interact via the formal single bonds and how far does an extra charge or an excitation delocalize over the chain. (2) Large... 

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