Propene, from cyclopropane

The formation of the diene in the isomerization of vinylcyclopropane is analogous to the formation of propene from cyclopropane. The reaction has a higher energy of activation than the ring-closure reaction. Fig. 3 gives an interpretation of these results in terms of the biradical mechanism. 

The literature offers an alternative pathway for the formation of propenes from cyclopropanes in the presence of electron sources as mentioned earlier rearrangement of the trimethylene radical anion 175a to give 176a is the important step, see also pathway B, Scheme 17 . ... 

The adsorption of cyclopropanes at room temperature has been characterized by infrared spectroscopy for a number of silica-supported catalysts, viz., Ni (86), Pt (86), Pd (266), and Rh (91). The spectra are identical with those obtained from the adsorption of propene on the same metals. They give absorptions from CH3 groups showing that the C3 ring has been opened, and the nature of the spectra has already been discussed (140, and Part I, Section Vl.C.l.b). Typical spectra of species formed from cyclopropane on Ni/Si02 and Pt/Si02, obtained by Ward at room temperature, are shown in Figs. 9C and 9D. 

McGee also found the cyclopropane/propene ratio to decrease with increasing pressure in the photolysis of cyclobutanone. However, his data indicated that the change is entirely due to an increase in propene formation, while cyclopropane formation is claimed to be independent of pressure. McGee suggested, on the basis of these results, that propene and cyclopropane were not formed from the same excited state. The deuterium content of the olefin, formed in the photolysis of cyclopentanone-2,2,5,5-rf4, also indicates that the hot cycloalkane is not the only source of the CH2 = CH(CH2) 4CH3 product - . 

The electronic state responsible for reactions II and III is not so well known and it is almost certain that there are essential differences in this respect between the different cyclic ketones. On the basis of the different pressure dependence of propene and cyclopropane formation in the direct photolysis of cyclobutanone, McGee concluded that cyclopropane is formed from the excited singlet state, while propene is considered to be a triplet product. 

A question arises here as to whether cyclopropane parent ions acquire the propene-ion structure prior to or during reaction. The question cannot be answered from comparison of reactions in pure propene and cyclopropane systems, since neutral reactants are also different in these two... 

Complexes 29 and 30 are decomposed photochemically to give the products expected as the latter stage of an olefin metathesis reaction, namely ethene from 29, propene from 30, and both ethene and propene from 31, but their thermal decomposition at 80°C gives cyclopropane and propene from 29, and butenes from 30 and 31 (Ephritikhine 1976, 1977 Adam 1980). 

The deamination of n-propylamine by nitrous acid and the deoxideation of n-propoxide both give propene and cyclopropane as the elimination products in a ratio of 9 1 (refs. 619, 620). A similar product ratio is obtained from the thermolysis of 1-diazopropane and this raises the possibility that carbenoid intermediates are also involved in the former reactions. However, the products of deoxideation of 1,1-dideuteropropanol are consistent with a carbonium-ion mechanism involving a 1,3-elimination to give the cyclopropane,... 

The rate of conversion from cyclopropane to propene in the gas phase at constant temperature is a first order reaction. From the information in the graph, which statement about the half-life of the conversion reaction is true ... 

Figure 5. a, NMR spectra (at 100 MHz, in CCI under pressure) of a mixture of gaseous propane, propene, and cyclopropane, b, Proton noise-decoupled NMR spectra (at 15.4 MHz, in CCl under pressure) of some of the reaction products obtained from the electrolysis of the [2,2-d,] butyrate ion Expansion, proton-coupled deuterium resonances. (Reproduced from Ref. 6. Copyright 1980, American Chemical Society.)... 

Catalytic amounts of cobalt halides react with methyl lithium and tominal aliphatic epoxides to produce methyl ketones and alcohols. The thermochemistry and structures of the metallocycle and metal alkene isomers of formula Co(C3H6) from reaction of gaseous Co and propene or cyclopropane in a flow system have been studied. ... 

Figure IX-E-4 shows as a function of wavelength at two pressures the ratios of propene to cyclopropane products that are formed in alternative pathways for reaction of the vibrationally excited cyclopropane molecule. A large increase in this ratio is seen as the excitation energy is increased in photolysis at the shorter wavelengths. A cyclopropane molecule that is vibrationally richer results as the quantum energy is increased. A somewhat more efficient quenching of the vibrationally excited cyclopropane can be seen for the data from 11 Torr of cyclobutanone (dashed curve) compared to those for 5 Torr (solid curve). One expects that an atmosphere of air will result in more significant...

Figure iX-E-4. The ratio of propene/cyclopropane as a function of wavelength in the photolysis of cyclohutanone at two pressures. Propene and cyclopropane both can arise from process (II) cyclopropanone + /ju —> excited cyclopropane + CO (II). Collisional stabilization of the excited cyclopropane becomes less effective (and decomposition more effective) in photolysis at the shorter wavelengths figure from Calvert et al. (2008). 

Stabilization of the cyclopropane molecule. For example, with cyclohutanone photolysis (4.5 Torr) at 265.4 nm, the addition of 33.5 Torr of hexane decreased the ratio of propene to cyclopropane from 1.04 to 0.56 (McGee, 1968). 

Self-Test 13.7B Cyclopropane isomerizes to propene in a first-order process. How long does it take for the concentration of cyclopropane to decrease from 1.0 mol-L 1 to 0.0050 mol-L 1 at 500.°C Use the data in Table 13.1. 

Sketch plausible transition states for (a) the dissociation of a molecule in the gas phase (b) the reaction of cyclopropane to give propene (c) the isomerization of CH3CN to CH3NC (d) the desorption of an atom from a surface (e) the dissociation of an adsorbed molecule such as CO on a metal surface. 

In the propene reaction, both YCH2 and YC3H4 were again observed. The YC3H4 data at EC(J = 25.2 kcal/mol were similar to those observed for the cyclopropane reaction at 18.5 kcal/mol. From the difference in enthalpies... 

Various alkyl- and aryl-substituted [3]radialenes could be prepared from 1,1-dihaloal-kenes using organometallic pathways. Hexamethyl-[3]radialene (25), the first [3]radialene to be synthesized, was obtained in a very low yield by treatment of l,l-dibromo-2-methyl-1-propene (22) with butyllithium8,9. The lithium carbenoid 23 and the butatriene 24 are likely intermediates of this transformation (Scheme 2), the former being the source of an unsaturated carbene moiety which is transferred onto the latter. However, the outer double bonds of 24 are more readily cyclopropanated than the central one. 

The versatile Ti(II) chemistry available using preformed (alkene)Ti(OiPr)2 species was opened up by the discovery of the Kulinkovich cyclopropanation reaction [55]. Since 1995, Sato and collaborators have developed a wide range of elegant and synthetically useful reactions based on the Ti(OiPr)4/iPrMgCl reagent [56]. In particular, it was reported that the Ti(II) complex (q2-propene)Ti(OiPr)2, preformed from Ti(OiPr)4 and 2 equivalents of iPrMgCl, reacts with allylic compounds, such as halide, acetate, carbonate, phosphate, sulfonate, and aryl ether derivatives, to afford allyltitanium compounds as depicted in Scheme 13.27 [57]. 

Special interest attaches to the cyclic aliphatic hydrocarbons. Cyclopropane can be converted to oligomers by cationic catalysis [75, 76], and these appear to be essentially linear but whether they are really different from the polypropenes formed under the same conditions from propene is not yet settled. The initiation most probably involves formation of a non-classical cyclopropyl ion [77], as in alkylations with cyclopropane [78],... 

Accompanying this trend is a monotonic decrease in the internal angle at the adjacent position (P), from 119.6° in tetralin to 113.0° in cyclopropabenzene (Figure 16). The bond lengths at the ring fusion are demonstrably shorter in cyclopropabenzenes. This has caused some discussion of bond fixation in cyclopropabenzene however, parallel effects are seen for cyclopropane and cyclo-propene among cycloalkanes and cycloalkenes, respectively. Thus, the shorter bonds in cyclopropabenzene are expected or rationalized by simple rehybridization independent of any bond fixation. 

As mentioned above, the conversion of cyclopropane to propene radical cation has been investigated by ab initio calculations. The general course of this reaction was confirmed, or anticipated, by product studies in the electron transfer-sensitized conversion of 1,1,2,2-tetraphenylcyclopropane (37) to 1,1,3,3-tetra-phenylpropene (38). The sequence of the key steps, migration versus ring opening cannot be derived from the results. In the case of 37, the four phenyl substituents may actually favor a ring-opened bifunctional radical cation. 

Of the many substituted and functionalized alkenes that have been combined with diazo dipoles to give A -pyrazolines or products derived from them (i.e., A -pyrazolines, pyrazoles, cyclopropanes), only a selection will be mentioned. These include ot-alkylidene-cycloalkanones (62), -flavanones, -thioflavanones, -chroma-nones, and thiochromanones (63,64) a-arylidene-indanones and -indolones (65) diarylideneacetones (66) l-benzopyran-2(77)-ones (coumarins) (67,68) 4-nitro-1,2-oxazoles (69) 2-alkylidene-2-cyanoacetates (70) dimethyl 2,3-dicyanofuma-rate (71) tetracyanoethylene (72) tetraethyl ethylenetetracarboxylate (72) 1,4-quinones (35,73-75) 2-X-l,l,l-trifluoro-2-propene [X = Br, (76), SPh, SOPh, S02Ph (77)] nitroalkenes (78) including sugar nitroalkenes (79) 1-diethoxyphos-phoryl-1-alkenyl-sulfoxides (80) methyl 2-(acetylamino)cinnamate and -acrylate... 

Problem 9.24 The carbene iCCl generated from chloroform, CHCI, and KOH in the presence of alkenes gives substituted cyclopropanes. Write the equation for the reaction of CClj and propene. <... 

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