The Mercury-Photosensitized Decomposition of Propane: A Mass Spectrometric Study at Low Pressures: Part I

Abstract

I t is found that the primary decomposition involves the cleavage of a C-H bond. Both primary and secondary hydrogen atoms are lost. The relative rates of the two processes could not be determined accurately but are estimated to be approxin~ately 1:l. I t is found that a t least 70% of the secondary reactions involves the interaction of hydrogen atom with a propyl radical. The main reaction is the re-formation of propane. An important disproportionation of hydrogen atoms with propyl radicals leading to propylene is shown t o occur. The atomic cracking reaction H + C3H7 + C3Hs* + CzHs + CH3 is also observed. Using mixtures of C3H8 and C3Ds the relative cracking rate of n-propyl-t o isopropyl-derived propane is determined t o be equal to 5. This result is compared with theoretical predictions.

Free Radicals by Mass Spectrometry: Xxxi. H-Atom and D-Atom Removal in the Mercury-Photosensitized Decomposition of Isobutane and Deuteroisobutanes

“…The large effect of deuterium substitution on the frequency of bond rupture in isobutane is similar to that reported recently for propane (6,7). The ratios of secondary to primary bond cleavage in (CH3)zCHZ and (CH?…”

“…As for other paraffins, the primary dissociation in isobutane appears to involve only C-H bonds, but it is not clear whether the H-atom removed in this reaction is uniquely the tertiary H-atom, or whether removal of a primary H-atom occurs concurrently. Recent work on the quenching cross sections of deuterated propanes shows that the primary interactions of Hg3P1 with propane occurs mainly a t the secondary C-H bonds (2), but the actual bond cleavage may occur a t either position in a ratio not far from unity (6,7). Taking account of the number of primary and secondary hydrogens available, it appears that secondary bond rupture is favored by a significant factor.…”

MERCURY-PHOTOSENSITIZED DECOMPOSITION OF ALIPHATIC HYDROCARBONS—RADICAL DETECTION WITH ETHYL-CARBON-14 RADICALS1

“…= 0.55 has been obtained. 18 In this case the relative yields were determined by the methyl-d8 saturation technique19 and by analysis of the hexane fraction as well, comparable results being obtained by the two methods.…”