ION-MOLECULE REACTIONS IN CYCLOHEXANE
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Mass Spectrometric Investigation of Ion-Molecule Reactions in Cyclohexane'"
by Fred P. AbramsonIb and Jean H. Futrell Aerospace Research Laboratories, Chemistry Research Laboratory, O&e of Aerospace Research, Wright-Patterson Air Force Base, Ohio 46433 (Received March 27, 1967)
The various ion-molecule reactions of fragment ions produced from cyclohexane have been investigated in conventional high-pressure mass spectrometers as well as in a tandem mass spectrometer. The results from the single-stage instruments showed that (i) all fragment, ions with less than six carbon atoms react with cyclohexane, (ii) the major secondary ions are CsH1l+ and C6HlO+ with minor amounts of C4H9+,(iii) C4H8+and C3H6+ fragment ions react in a similar way to 1-butene and propylene parent ions, respectively, and (iv) there is a net charge exchange reaction of parent ions which will cause the ratio of isotopically substituted cyclohexane ions to differ considerably from the ratio of the neutral molecules in an isotopically mixed system. All fragment ions react via the C& 12 --t R H C8Hll+, and C3H6+and C4Hs+ions also hydride transfer reaction, R + abstract H2- to product CsHlo+.
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Introduction The radiolysis of cyclohexane has been investigated for many years, but there have been few quantitative studies of ionic reactions in the cyclohexane system. Milhaud and Durup2 briefly studied ion-molecule reactions of cyclohexane in a mass spectrometer arid reported that C6HlO+ and C6Hll+ were produced by secondary reactions involving H2- and H- transfer from neutral cyclohexane molecules. Doepker and Ausloos3 have also observed the Hz- reaction in the radiolysis of cyclohexane vapor using mixtures of normal and deuterated cyclohexane. Ausloos and Lias' further observed reactions of C6Hl2+ which involve the transfer of Hz to unsaturated molecules. We have also examined5 these reactions and have found an He transfer reaction from cyclohexane ions in addition to €I2 transfer reactions. In the present study we have investigated the individual reactions of each fragment ion by impacting that ion onto cyclohexane in a tandem mass spectrometer. Additionally, we have obtained the over-all disappearance cross sections for many of the fragment ions from cyclohexane in conventional high-pressure mass spectrometric experiments. Finally, we have searched for possible structural effects in the reactions of GHaf and C4Hg+ions formed in the decomposition of cyclohexane by comparing the ratios of H2-/H- transfer from these ions with the ratio for
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molecular ions formed from stable olefin and cyclane species.
Experimental Section The ARL tandem mass spectrometer was used for studying the individual ion reactions. The instrument has been described previously6 and the experimental techniques are also reported.' For all the experiments in this paper, the ion energy was 0.3 f 0.3 ev and pulse counting was used in all cases. The measurements of reaction cross section were made using a specially modified Bendix Alodel 12-101 time-of-flight mass spectrometer which permits operation at2source pres(1) (a) Presented a t the 152nd National Meeting of the American Chemical Society, New York, N. Y., Sept 1966; (b) National Academy of Science-National Research Council Postdoctoral Research Associate, 1965-1966. To whom correspondence should be addressed a t Consolidated Electrodynamics Corp., 1500 S. Shamrock Ave., Monrovia, Calif. 91017. (2) J. Milhaud and J. Durup, Compt. Rend., 260, 6363 (1965). (3) R. D. Doepker and P. Ausloos, presented a t the 148th National Meeting of the American Chemical Society, Chicago, Ill., Aug-Sept 1964. (4) P . Ausloos and S. G . Lias, J . Chem. Phys., 43, 127 (1965). (5) F . P. Abramson and J. H. Futrell, J . Phys. Chem., 71, 1233 (1967). (6) (a) J. H. Futrell and C. D. Miller, Rev. Sci. Instr., 37, 1521 (1966); (b) C. D. Miller, F. P. Abramson, and J. H. Futrell, ibid., 1618 (1966). (7) F. P. Abramson and J. H. Futrell, J . Chem. Phys., 45, 1925 (1966).
Volume 7 1 , Number 18 November 1967
FREDP. ABRAMSON AND JEAN H. FUTRELL
3792
sures up to 1 torr.* Electrons (100 ev) were used a t a very low (
