Labelled propene

The structure and properties of the initial nickel atom-propene complex has received detailed attention by Skell. The use of isotopically labeled propenes demonstrated that exchange occurs between the 1- and 3-positions but not between either the 1- and 2- or 2- and 3-positions (10) ... 

The occurrence of a symmetrical intermediate at an early stage of the reaction with a variety of catalysts however, is unmistakably indicated by experiments with 13C and 14C-labelled propene. 

The kinetics of the parallel formation of by-products is generally similar to the kinetics of the main reaction (i.e. rate independent of the oxygen pressure and first order with respect to propene), which presumes identical reaction steps. A study of the origin of acetaldehyde and formaldehyde carried out by Gorshkov et al. [144] is of interest in this connection. 14C-Labelled propene was oxidized over a bismuth molybdate catalyst at 460° C the results showed that acrolein, acetaldehyde and formaldehyde are formed via a symmetrical intermediate, presumably one and the same intermediate. The study, moreover, shows that acetaldehyde is exclusively formed from this intermediate, while formaldehyde may also be formed from the aldehyde group of acrolein and the methyl group of acetaldehyde. 

Early kinetic studies on the structural isomerization of cyclopropane to propene provided estimates of activation parameters73 75 and prompted speculation that the reaction might well involve a trimethylene diradical intermediate. This possibility seemed reinforced when the thermal interconversion of the els and trans isomers of l,2-d2-cyclo-propane at 414 to 474 °C (equation 1) was reported in 195876. This structurally degenerate isomerization was found to be substantially faster than conversion to deuterium-labeled propenes—about 24 times faster at the high pressure limit76 77. 

Direct evidence for the formation of allylic species on a solid surface was given by Dent and Kokes (21) for zinc oxide by using labeled propene, as expressed in Eqs. (10) and (11). In the IR absorption spectra, an O—D... 

A number of classical studies were performed in the 1960s in which isotopically labelled propenes were fed to CU2O or bismuth molybdate catalysts. One series... 

Propene.—Dent and Kokes demonstrated most elegantly, using i.r. spectroscopy and 6 selectively labelled propenes, that on adsorption propene forms both a ff-complex (vc=c shifted 30 cm from the value in gas phase) and a TT-allyl species ( CH2—CH—CH2, i c = c shifted 100 cm" ). The latter had a saturation coverage of 30% and was analogous to the 7r-allyl ligands of transition metal complexes. They showed that it displaced type (/) hydrogen to C3H5 H... 

Samples were prepared by adsorption of 9 molecules of benzene and 1 molecule of labelled propene per u.c. of a ZSM-11. This mixture was converted to cumene 1 or 2 at room temperature giving final molar ratio benzene/cumene = 8 1. 

C-labeled propene was also converted with the cobalt catalyst. The results resembled those obtained with ethene (Table 3). However, there were noticeable... 

Percy and Walter converted a mixture of doubly labeled ethene ( CH2 CH2 2 mol percent), CO (24.5 mol percent) and H2 (73.5 mol percent). The propene in the effluent from runs with low (3 to 4 percent) conversions was trapped and analyzed with NMR to determine the distribution of C at each carbon position in the propene. It was possible to quantify the amount of each of the eight isotopomers that can result from various combinations of C and C that were present. Singly labeled propenes were formed from the doubly labeled ethene this required that some ethene dissociates to form C fragments. No evidence was obtained that would indicate that two Cj units, one from CO and one from a C2 unit, recombine to give C2H4 in the product. Thus, ethene is incorporated in part as C2 units and in part by dissociation to Cj units. Incorporation of single Cj units from ethene is equally probable at the three carbon positions of the propene that is eventually formed. The authors state that they see no contradiction between any of their data and the widely accepted carbide mechanism for FTS. 

C-Labeled propene incorporated to produce hydrocarbons with a constant molar radioactivity just as was observed with labeled ethene. However, propene initiated the formation of products (one of 12 molecules) to a smaller extent than ethene (one of four to five molecules). 

Early work using and deuterium labelled propene and butene quickly established that two olefinic bonds are switched between four carbon atoms, the integrity of all other bonds within the alkenes remain intact [18]. 

Gabrienko et al. have used the C-label serambling from the position 3 to the position 1 in the C-labeled propene adsorbed on zinc oxide has been performed with and C ssNMR in situ. This allowed the characterization of this mechanism. ... 

Mol et al. (61) analyzed the products formed in the heterogeneously catalyzed metathesis of propene labeled with 14C. With propene labeled in the 2-position there will be, in the case of a transalkylation reaction, an equal distribution of the radioactivity over the products ... 

Oxidation of propene labelled with C(CH3-CH- CH2) yields acraldehyde (88 %), acetone (10 %) and propanal (2 %). The labelled acraldehyde consists... 

The absolute-energy minima labeled as a in Figures 1.7a,b correspond to 0i —60° for the re monomer coordination and are sketched in Figures 1.4 and 1.6a, respectively. These models minimize the interactions between the growing chain (at 0i —60°) and the methyl of the propene monomer (re coordinated). Therefore, these are assumed to be preinsertion intermediates suitable for the re monomer primary insertions. 

Figure 1.8 Approximated transition states for primary propene insertion for model complexes with (a) isopropyl-bis(l-indenyl) ligand (isospecific) for the (R, R) coordination and (b) iso-propyl(cyclopentadienyl-9-fluorenyl) ligand (syndiospecific) for the R chirality at metal atom. Corresponding preinsertion intermediates, labeled a in Figures 1.7a,b, are sketched in Figures 1.4 and 1.6a, respectively.

The energy minima labeled as a, b, and c in Figure 1.9a, corresponding to 0O 0°, are coincident with those labeled with the same letters in the energy plot of Figure 1.7a. As already cited, the absolute minimum energy (labeled a) corresponds to the preinsertion intermediate for propene primary insertion with re enantioface, which is sketched in Figure 1.4. 

The use of deuterium labels in propene can help to establish the epimerisation of the intermediate alkyl species. 

Example The transfer of a D compared to the transfer of an H during propene loss from partially labeled phenylproylethers is accompanied by an isotope effect, the approximate magnitude of which was estimated as follows [74]... 

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