Butadienes results

Figure 14.12 Ultraviolet excitation of 1,3-butadiene results in the promotion of an electron from i / , the highest occupied molecular orbital (HOMO), to 1//3, the lowest unoccupied molecular orbital (LUMO).

In 1989 Jutzi et al. reported the reaction of decamethylsilicocene 50 with tri-n-butylphosphine selenide in benzene at room temperature, leading to almost quantitative formation of a 1,3,2,4-diselenadisiletane derivative 52, a head-to-tail [2+2] cycloaddition reaction product of the initially formed silaneselone 51.35 The intermediacy of silaneselone 51 was experimentally supported by the reaction in the presence of 2,3-dimethyl-1,3-butadiene resulting in the formation of the corresponding [2+4] cycloaddition reaction product 53 (Scheme 14). 

The polymerisation of butadiene results in a polymer with a narrow molecular weight distribution which can be difficult to process. Indeed, commercially available grades present a compromise between processibility and performance. Most polybutadiene rubbers are inherently difficult to break down during mixing and milling, have low inherent tack, and the inherent elasticity of the polymer gives poor extrudability. Peptisers can be used to facilitate breakdown and hence aid processing. 

The (RME) heterocycles can be used as sources for the unstable six-electron RM species. Deselenation of (RSbSe)3 in the presence of 1,3-butadienes results in the formation of cycloadducts of the stibinidene RSb,... 

EXAMPLE 2.9 Degradation of 1,3-butadiene resulting from a spill (linearized source-sink terms)... 

Leavens et al. (1996a, 1997) and Leavens and Bond (1996) further explored the metabolic interactions between butadiene and styrene in male B6C3Fj mice exposed to mixtures of butadiene and sty rene by inhalation. At steady state, significant inhibition of butadiene metabolism by styrene was observed with mixtures of 1000 ppm butadiene and 250 ppm styrene, but not with 100 ppm butadiene and 250 ppm styrene. Inhibition by butadiene of sty rene metabolism was evidenced by the significant increase in styrene blood concentrations (42% above that in mice exposed to styrene only) in the exposure to 1000 ppm butadiene and 250 ppm styrene. These authors concluded that while exposure to mixtures of sty rene and butadiene results in inhibition of metabolism of both sty rene and butadiene, interactive effects are seen only at high concentrations that are of little relevance to human exposure. 

Tamao et al,83 found that a higher coordinated silylene 119 can be formed from penta-coordinated silane 118 (Scheme 31). Warming a solution of 118 in toluene or dimethylformamide in the presence of diphenylacetylene or 2,3-dimethyl-l,3-butadiene resulted in the formation of silylene-trapping products 120 and 121. Interestingly, no 1 1 reaction product between the silylene and the acetylene was isolated. Thus, it must be concluded that the insertion of silylene 119 into a Si-C bond of initially formed silacyclopro-pene is faster than the addition to the triple bond of the acetylene so that the silacyclopropene cannot be isolated under the reaction conditions. 

When this reaction was carried out in the presence of copper(II) chloride as oxidant, efficient catalytic production of bis-2,3-chloromethyl-1,3-butadiene resulted (Scheme 13).46... 

Thermolysis of a toluene solution of 30 at 90 °C in the presence of excess butadiene results in the liberation of 1 equivalent of ethene and the formation of the reactive Cp2Hf(r 2-CH2 = CH2) intermediate, which subsequently reacts with butadiene to form a 2-vinylmetallacyclopentane complex 31, which is however unstable under the reaction conditions and was isolated as the corresponding isomeric (r 3-allyl)hafnocene complex 32 35... 

Complexes with 1,3-dienes. The reaction of activated Mg (11, 307) in THF at 25° with (E,E)-1,4-diphenyl-1,3-butadiene results in the deep red complex (1,4-diphenyl-1,2-butene-1,4-diylmagnesium). This halide-free bismagnesium reagent (1) forms a 1,4-adduct with a, co-dibromoalkanes, which undergoes intramolecular... 

Addition of IC1 and IBr to 1 -methyl-4-r-butylcyclohexene has been studied. The higher stereoselectivity of the IBr addition is interpreted on the basis of the higher softness of Br relative to Cl-512. Addition of IC1, IBr and t-BuOI to 1,3-butadiene results in a mixture of 1,2- and 1,4-addition according to Markovnikov513. Addition of IC1 and ICN to (perfluoroakyl)alkyne proceeds regioselectively with the iodine attached to the terminal carbon514. 

Electrical conductivity increased sharply on adding butadiene (Figure 10) and then decreased to its original level further addition of butadiene resulted in the same effect. 

A process for the production of 1,3-butadiene results from the catalytic dehydrogenation of 1-butene according to the reaction... 

The hydrogenation of a conjugated double bond can occur either by 1,2- or 1.4-addition of the first molecule of hydrogen. The hydrogenation of substituted butadienes results in the formation of all possible dihydro products4. The 1,4-product may also be formed by 1,2-addition with subsequent double-bond migration. 

The addition of 1,1,1-trichloroethane and 1,1,1,3-tetrachloropropane to conjugated diene, 1,3-butadiene results in 1,4-conjugated addition and formation of an unsaturated polychlorocompound [36] (Fig. 28). 

Figure 4.12 C1-C2-C3-C4 dihedral angle (solid line) and terminal C-C bond twist angles (dashed and dotted lines) as a function of time after photoexcitation of butadiene. Results are averaged over 10 initial conditions. The dashed and dotted lines are the average of the twist angle for the more- and less-twisted terminal bonds, respectively. The definition of the terminal C-C bond twist angle is illustrated in the inset and described in the text. Asymmetric twisting around a single terminal C-C bond begins about 40 fs after excitation. Eventually, the more-twisted bond tends toward 90° whereas the less-twisted bond remains nearly planar.

Figure 4.14 Population on Sq (solid line), Si (dashed line), and S2 (dotted line) as a function of time after photoexcitation of butadiene. Results are averaged over 10 runs. Immediately upon excitation to the bright excited state, there is nearly diabatic population transfer to Sg. Quenching from S2 to Si begins about 70 fs after photoexcitation and quenching to the ground state begins roughly 30 fs later.

Butyllithium-initiated homopolymerisation of butadiene results in a BR polymer containing random distributed cis-1,4, trans-1,4 and 1,2-BR or vinyl-BR units. The concentration of the catalyst modifier and the polymerisation temperature (between 40°C and 75°C) determine the concentrations of the three different components. Thus, BR rubber is in fact nearly always a terpolymer and its Tg-value can be described by means of the Gordon-Taylor relation [7]. This relation is written in its general form as ... 

But, 1,2- or vinyl BR can be polymerised in the atactic, the syndiotactic or the isotactic form. Hence, five different configurations can be obtained by polymerisation reactions with butadiene (CH2=CH-CH=CH2) as monomer. The product obtained depends on the catalyst system used but is usually a mixture of 1,4 cis-, 1,4 trans- and atactic 1,2-BR. The commercial processes using Co-, Ni- or Ti-based catalyst systems, for instance, produce BR with a 1,4 cis-BR content higher than 90 %wt. But butyllithium initiated homopolymerisation of butadiene results in a product with 1,4 trans-BR contents up to 60 %wt. 

Metalated PIB obtained by one-pot dehydrochlorination-metalation of tert chlorine-ended PIB by potassium-t-amylate/nBuLi and tBuOK/nBuLi mixtures was used to initiate the anionic polymerization of butadiene resulting PIB-polybutadiene block copolymers. ... 

The NEER principle implies that each type of conformer yields its own specific assortment of photoproducts. The primary product composition originating from irradiation thus should form a qualitative and quantitative reflection of the composition of the ground-state conformational equilibrium. Hammond and Liu (64) even followed a comparable line of thought in the interpretation of the product formation resulting from triplet sensitized excitation of butadienes. Results of some further studies, in particular those of Baldwin (65) and of Dauben (66), brought additional support to the validity of the NEER hypothesis. Baldwin found a linear relationship between the optical rotatory power of a-phellandrene In solution at various temperatures and... 

Day and Futamura (1986) evaluated the impact of variation in 1,2-butadiene and styrene content in SBR on the properties of a compounded formulation. Briefly, (1) an increase in styrene produced an increase in tensile strength, (2) an increase in vinyl-1,2-butadiene resulted in a drop in both tear strength and ultimate elongation, and (3) at equal Tg, neither vinyl-1,2-butadiene nor styrene level affected the formulation s hysteretic properties. 

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