Olefins modeling

Recently, Kennedy and Rengachary11 studied cationic olefin model and polymerization reactions. Important conclusions of the model study were ... 

Several studies characterizing the reactions of alkenyl radicals with quinone dumines and quino-neimines were published in the late 1970s. Quinone dumines react with allylic radicals yielding both the reduced PPD and the alkylated product. In these experiments 2-methyl-2-pentene served as a model olefin (model for NR). Samples of the olefin and quinoneimines or quinone diimine were heated to 140°C. Isolation and analysis of products demonstrated that 40%-70% of the imine or diimine was reduced to the corresponding PPD, while 20%-50% was isolated as the alkylated product. This alkylation reaction (via an allylic radical) represents the pathway to the formation of rubber-bound antidegradant. ... 

Linear dienic conjugated systene were found very reactive also towari oxygen. Some model compounds, i. e. (UI,a), 2,4-hexadiene and 2,5-dimethyl-2,4-hexadiene, dissolved in n-heptane, reacted quickly with a stream of oxygen at 75 °C (Fig. 34). Reference was made to an olefinic model compound, i. e. NB, which exhibited practically no reactivity under the adopted conditions. Figure 34 shows that the higher the methyl content of the nmdel compound the faster the reaction with O2. 

More precisely, the rate of ozone formation depends closely on the chemical nature of the hydrocarbons present in the atmosphere. A reactivity scale has been proposed by Lowi and Carter (1990) and is largely utilized today in ozone prediction models. Thus the values indicated in Table 5.26 express the potential ozone formation as O3 formed per gram of organic material initially present. The most reactive compounds are light olefins, cycloparaffins, substituted aromatic hydrocarbons notably the xylenes, formaldehyde and acetaldehyde. Inversely, normal or substituted paraffins. 

As can be seen from Figure 4, LBVs for these components are not constant across the ranges of composition. An iateraction model has been proposed (60) which assumes that the lack of linearity results from the iateraction of pairs of components. An approach which focuses on the difference between the weighted linear average of the components and the actual octane number of the blend (bonus or debit) has also been developed (61). The iadependent variables ia this type of model are statistical functions (averages, variances, etc) of blend properties such as octane, olefins, aromatics, and sulfur. The general statistical problem has been analyzed (62) and the two approaches have been shown to be theoretically similar though computationally different. 

T[[dotb]he nature of the initial attack by the water (eq. 10) is a matter of some controversy (205,206). Stereochemical and kinetic studies of model systems have been reported that support trans addition of external water (207,208) or internal addition of cis-coordinated water (209), depending on the particular model system under study. Other paHadium-cataly2ed oxidations of olefins ia various oxygen donor solvents produce a variety of products including aldehydes (qv), ketones (qv), vinyl acetate, acetals, and vinyl ethers (204). However the product mixtures are complex and very sensitive to conditions. 

The mechanisms for the reaction of sulfur with alkanes and unsaturated compounds are highly speculative, being strongly influenced by the specific stmcture of the substrate and by the conditions (particularly temperature) of reaction. Alkane (4), olefin (5), animal fat (6), and vegetable oil (7) sulfurization have been extensively studied because these reactions are models for vulcanization. Moreover, the products are used as lubricant additives. 

One development involves the use of vitamin B 2 to cataly2e chemical, in addition to biochemical processes. Vitamin B 2 derivatives and B 2 model compounds (41,42) cataly2e the electrochemical reduction of alkyl haUdes and formation of C—C bonds (43,44), as well as the 2inc—acetic acid-promoted reduction of nitriles (45), alpha, beta-unsaturated nitriles (46), alpha, beta-unsaturated carbonyl derivatives and esters (47,48), and olefins (49). It is assumed that these reactions proceed through intermediates containing a Co—C bond which is then reductively cleaved. 

It is not feasible to model the reaction of each hydrocarbon species with oxides of nitrogen. Therefore, hydrocarbon species with similar reactivities are lumped together, e.g., into four groups of reactive hydrocarbons olefins, paraffins, aldehydes, and aromatics (32). 

Recycles are meticulously accounted for because they load equipment and draw utilities. An olefin plant sustaining relatively low conversion per pass often builds up large amounts of unreacted feed that is recycled to the steam crackers. With utilities charged to ultimate products, these recycles would seem to the model to be free. The model would likely opt for very low conversion, which usually gives high ultimate yield and saves feedstock. Assigning the utility costs to users causes the compressor to pay for the extra recycle and the model raises conversion to the true optimum value. 

During the early development of the Jacobsen-Katsuki epoxidation reaetion, it was elear that trans-disubstituted olefins were very poor substrates (slow reaetion rates, low enantioseleetivity) eompared to cis-disubstituted olefins. The side-on approaeh model originally proposed by Groves for porphyrin epoxidation systems was used to rationalize the differenees observed in the epoxidation of the cis and trans-disubstituted elasses (Seheme 1.4.7). ... 

This model prediets that tri-substituted and tetra-substituted olefins would also be poor substrates. Thus it was not until 1994 that a study in the epoxidation of higher substituted olefins appeared. Indeed Jaeobsen revealed that tri-substituted olefins, and even tetra-substituted olefins ean be excellent substratesA new model was put forth that encompasses a skewed side-on approach of tri-substituted olefins to the Mn-oxo eomplex. The observation that certain tetrasubstituted olefins undergo epoxidation with good enantioseleetivity suggests that further studies are needed in order to fully understand the transition state geometry of the catalyst and substrate. 

Dihydronaphthalene is often used as a model olefin in the study of epoxidation catalysts, and very often gives product epoxides in unusually high ee s. In 1994, Jacobsen discovered in his study on the epoxidation of 1,2-dihydronaphthalene that the ee of the epoxide increases at the expense of the minor enantiomeric epoxide.Further investigation led to the finding that certain epoxides, especially cyclic aromatically conjugated epoxides, undergo kinetic resolution via benzylic hydroxylation up to a krei of 28 (Scheme 1.4.9). 

Thermal stabilization of polyolefins has been first demonstrated for low-molecular models-normal structure alkanes [29]. It has been shown that metallic sodium and potassium hydroxide with absorbent birch carbon (ABC) as a carrier are efficient retardants of thermal destruction of n-heptane during a contact time of 12-15 s up to the temperature of 800°C [130]. Olefins and nitrous protoxide, previously reported as inhibitors of the hydrocarbon thermal destruction, are ineffective in this conditions. 

The Simple Model RFG required the addition of oxygenates and it limited the amount of benzene, sulfur, olefins, and T. The RVP was also lowered for six months during the summer period. Given these requirements, companies can choose to comply on a per-gallon basis (Table 10-4) or adopt the 1990 industry average basis (Table 10-5). 

Starting January 1998, the EPA s Complex Model went into effect. The Complex Model provides a set of equations that predict VOC, NO, and toxic emissions, using eight gasoline properties. These properties are RVP, oxygen, aromatics, benzene, olefins, sulfur, E200. 

The elegant, enantiospecific synthesis of biotin (1) by Hoffmann-La Roche1 is based on a strategy that takes advantage of the powerful intramolecular nitrone-olefin cycloaddition reaction. Our analysis begins with model studies in which the straightforward conversion of L-cysteine (2) into aldehyde 3 (see Scheme 1) constitutes... 

The 1,5 relationship between the olefin and keto groups in 13 satisfies the structural prerequisite for the oxy-Cope transform,11 and, like the first synthesis of periplanone B by Still,9 Schreiber s strategy recognizes that an anionic oxy-Cope rearrangement could provide a powerful and direct method for the assembly of cyclode-cenone 13. On the basis of the model study described previously, it was projected that deprotonation of the free hydroxyl group in 14... 

Nothing is known about the identity of the iron species responsible for dehydrogenation of the substrate. Iron-oxo species such as FeIV=0 or Fem-OOH are postulated as the oxidants in most heme or non-heme iron oxygenases. It has to be considered that any mechanistic model proposed must account not only for the observed stereochemistry but also for the lack of hydroxylation activity and its inability to convert the olefinic substrate. Furthermore, no HppE sequence homo-logue is to be found in protein databases. Further studies should shed more light on the mechanism with which this unique enzyme operates. 

Kennedy, J. P. and Rengachary, S. Correlation Between Cationic Model and Polymerization Reactions of Olefins. Vol. 14, pp. 1 —48. 

The model procedure described above is applicable to allylic alcohols, ethers, and acetates. The submitters results for the conversion of several such compounds to the corresponding olefins, performed on a smaller... 

Cobalt, nickel and copper naked metal clusters and olefin chemisorption models. G. A. Ozin, Coord. Chem. Rev., 1979, 28, 117-146 (45). 

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