Propene and cyclopropane

The occurrence of ions of m/e = 43 in propene mass spectra in excess of the contribution from the heavy isotope of the parent ion was recognized 

Percentage of four major reactions of C3H6 (produced from propene) with CaH  

Reactions of all the fragment ions produced by impact of 70—100 eV electrons have also been studied extensively [134, 277, 284—289]. According to Abramson and Futrell [284] who used a tandem mass spectrometer, many of the smaller fragment ions from propene are very reactive towards propene and, in fact, a total of 44 secondary ions have been detected with 100 eV electrons. MacKenzie Peers and Vigny [287, 288] have determined the disappearance cross-sections for the parent and all of the fragment ions. Results for some of these ions are given in Table 

Disappearance cross-sections of parent and some fragment ions in propene [288] 

Disappearance cross-section estimated by MacKenzie Peers from the formation cross-section for C4HS of Abramson and Futrell. 

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The difference between the energy of a molecule at 0 K and its enthalpy at 298 depends on the thermal contr ibution due to vibration at the two temperatures. If the molecule in question is rigid, with few vibrational degrees of freedom, this contribution will be small, as it is for propene and cyclopropane. For larger molecules with a good deal of vibrational freedom, the difference will be conespondingly larger. 

The simple hydrocarbon substrates included ethene, 1,2-propa-diene, propene and cyclopropane (22). Their reactivity with Sm, Yb and Er was surveyed. In contrast to the reactions discussed above, lanthanide metal vapor reactions with these smaller hydrocarbons did not provide soluble products (with the exception of the erbium propene product, Er(C H ) ). Information on reaction pathways had to be obtained primarily by analyzing the products of hydrolysis of the metal vapor reaction product. 

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. 

Overall ionic reactivity is also lower in cyclopropane than in propene [29, 175, 269, 285]. Total reaction rate coefficients and rate coefficients for some of the major reactions of the parent ions of propene and cyclopropane are given in Table 8. The lower reactivity in cyclopropane also seems to be pertinent to higher-order reactions. Thus, while poly-... 

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... 

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,... 

Vollmer, D.L., Rempel, D.L. and Cross, M.L. (1996) The rf-only-mode event for ion-chemistry studies in Fourier transform mass spectrometry the reactions of propene and cyclopropane radical cations with neutral ethene. International Journal of Mass Spectrometry and Ion Processes 157/158, 189-198. 

Systematic transmission spectroscopic studies of the transformations were carried out on the systems allene, propene, cyclopropane, zsopropanol and acetone over NaM,HM and NaHM [113-117], 1-butene over NaHY [117,118], allene, propene and cyclopropane over NaHY and NaHZSM-5 [116,117,119-122],neopentane over NaY, NaHY,NaHM and NaHZSM-5 [119,123,124],cyclohexene over HZSM -5 [ 119], 1 -hexene, cyclohexane, cyclohexene, cyclohexadiene and benzene over NaHY and NaHZSM-5 [117,125], allyl alcohol, acrolein and allene over HZSM-5 [ 126], allene and propyne over nonacidic zeohtes NaA, CoNaA, CoNaX, NaY and NaHY [121] and benzene, toluene, ethylbenzene, and cumene over HZSM-5 [127]. 

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.)... 

Cyclopropanes are formed by the intramolecular insertion of a carbene into a C—H bond. A MINDO/2 study of the rearrangement of singlet ethylmethylene to propene and cyclopropane revealed that olefin formation (hydrogen migration) presents no energy barrier, but a critical energy of 1.4 kcal mol was found in the pathway to cyclopropane formation. ... 

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). 

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