Propene, -2-methyl spectrum

A methyl-rich spectrum from propene adsorption had been earlier observed after hydrogenation during work on Pt supported on porous glass (250). The marked contrast between this spectrum and that from a n-propyl group chemisorbed on a Ni catalyst had led to the hypothesis that the former arose from chemisorbed 2-propyl species. It was subsequently shown to be caused instead by physically adsorbed propane that was present because of the greater propensity for complete hydrogenation of the initial surface species on Pt. 

Several years ago dimerization was essentially achieved (and is still currently performed) by means of acidic catalysts, sometimes as liquids but mainly as solids. However, in spite of its economic interest owing to its low price and low sensitivity to impurities, cationic oligomerization is limited in scope, the main drawbacks being its poor selectivity and low activity toward linear olefins. Organometallics of highly electropositive metals (aluminum, potassium) afford better selectivities but their specificity and their poor activity restrict their use to some specialized syntheses, e. g., dimerization of propene into 2-methyl-1-pen-tene (Al(/-Pr)3) or 4-methyl-1-pentene (K). Coordination catalysts offer a broader spectrum of activity (which is often the opposite of that observed in cationic reactions) and more diversified selectivities their practical use can be expected to grow. 

The solution is cooled in an ice bath and is stirred rapidly as 9.65 g (0.107 mole) of l-chloro-2-methyl-l-propene (isobutenyl chloride) [Aldrich] is added over a period of 5 min. The reaction can be followed by observing the changes in the IR spectrum of the solution. The carbonyl absorption bands characteristic of the anion are replaced by those typical of the product at 1998 and 1950 cm. Upon completion of the addition of l-chloro-2-methyl-l-propene, stirring at 0" is continued for 1 hr to ensure completion of the reaction. The resulting solution of dicarbonyl (Ti -cyclopentadienyl)(2-methyl-l-propenyI-KC )iron may be used directly without purification. Alternatively, the product can be isolated and purified by removing solvent under reduced pressure, followed by chromatogra(>Ay of the residue on 300 g of neutral activity III alumina. The column is made up in anhydrous diethyl ether, and after dissolving the crude product in petroleum ether, elution under N2 is carried out with this solvent. The product may 6e further purified by short-path distillation at pressures less than 10 mm (pot temperature less than 40°). It is then sufficiently pure to be stored at -20° for... 

The polymerization reaction is a sequence of different events, such as monomer insertions, site isomerizations, and chain release reactions. The polymer chain can be seen as a permanent picture of the sequence of these events, and it is possible to use a statistical approach to study their distribution along the chain to increase our knowledge on polymerization mechanisms. As a consequence, a mathematical model of the polymerization can be built by assigning a probability at each event in our system. In the case of propene homopolymerization, this approach is (largely) used to study the mechanisms governing the stereoselectivity of the catalyst from the NMR spectrum of the polymer. In fact, the type and the relative amount of the stereosequences present in the chain are obtained from the methyl region of the spectrum and are usually determined at the pentad level (see section II.G). This distribution can be studied using insertion probabilities for propene enantiofaces, which depend on the type of stereocontrol mechanism active for the catalytic... 

Early IR and UV-VIS spectroscopic studies on the formation of carbonium ions from triphenyl methyl compounds on zeolites, titania and alumina were carried out by Karge [111]. In 1979, upon interaction of olefins Hke ethene and propene with zeoHtes CoNaY, NiCaNaY, PdNaY and HY, the appearance of electronic bands between 230 and 700 nm was observed by Garbowski and PraHaud and attributed to an allylic carbenium ion which upon thermal treatment transforms into polyenyl carbenium ions and/or aromatic compounds [112]. These findings were corroborated and extended by studies of the interaction of propene, cyclopropane and frans-butene on zeoHtes NaCoY and HM [30]. In spite of the obscuration of the spectrum in the range between 450 and 700 nm by the threefold spHt d-d band of tetrahedraUy coordinated Co(II) ions in the case of zeoHte NaCoY,the development of bands near 330,385 and 415 nm was assigned to unsaturated carbocations. 

Further information may be extracted from the analysis of the fine structure of proton - coupled high resolution deuterium spectra. Thus, the proton-coupled deuterium spectrum of the methyl group of propene appears as a doublet of doublets (see inset to Figure 5), indicating that the position must be doubly deuterated. 

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