Cyclobutane from radiolysis

Enhancement of the total butene yield is observed when various additives whose ionization potential falls below about 9.4 e.v. are present during ethylene radiolysis (35). This is consistent with the above interpretation (Figure 2). In the vacuum ultraviolet photolysis of cyclobutane the yield of butenes varies with the ionization potential of the additives in the same way as observed here (12). The maximum enhancement corresponds closely to the yield of C4H8+, as expected from our mechanism. 

Among the simple cycloalkanes, we first discuss electron transfer from the three-to eight-membered cycloalkane prototypes to electron holes generated by radiolysis in different matrices, giving rise to the simple cycloalkane radical cations. Because of the significant interest they have attracted, the electron-transfer reactions of cyclopropane and, to a lesser extent, cyclobutane derivatives will be treated separately. Finally, electron transfer from some bicyclic hydrocarbons and the resulting radical cations will be discussed in a separate section (Section 2.4). 

Holroyd studied the type of the radicals formed in irradiated cyclopropane with the radical sampling technique and found several intermediates besides the cyclopropyl radical. Not all the hydrocarbons formed were identified but it was found that cyclopropyl and allyl radicals were both present in approximately a 1 1 ratio, indicating that ring-opening is a major process in cyclopropane. The extent of ring-opening decreases for cyclobutane and decreases further for cyclopentane. Similar results that the probability of C-C bond rupture falls from cyclopropane to cyclohexane were observed in the radiolysis of liquid cycloalkanes in an ESR study. ... 

The olefin F-cyclobutene, which would be derived from the parent compound by loss of F2, definitely is not produced. A standard sample of F-cyclobutene eluted between the peaks identified as Cr,Fi2 and C0Fi4, where no radiolysis product appeared. Since the parent F-cyclobutane tailed badly on the silica gel column used, the presence of other possible C4 fluorocarbons such as n-C4F8 or n-C4Fi0 could have been masked. 

We have verified this energy effect for the reaction of cyclobutane parent ions with 1-butene by increasing the collision chamber pressure by a factor of five. The ratio of mje = 84 to mje = 69 increased substantially over that shown in Table XVI. Unfortunately, because of the possibility of further ion-molecule reactions at the higher collision chamber pressure, this experiment is not definitive. Nevertheless, the data presented in Table XVI support the hypothesis that rearrangement of at least some of the cyclobutane parent ions to the iso-structure occurs prior to reaction. The relative amounts of the various isomeric structures formed in low-pressure mass spectrometric experiments may, of course, differ from the distribution in high-pressure radiolysis experiments. It is also quite possible that cyclic cyclobutane parent ions exist, but our study provides no evidence for their formation. 

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