An ion cyclotron resonance study of the structures of C7H7+ ions

Abstract

7) F. P. Lossing. personal communication. The value of 156 kcai mol-' for AHf(CH&H=N+HZ) was derived from the AP of m l e 44 in the mass spectrum of (CH3)zCHNHz. We thank Dr. Lossing for his assistance in performing this measurement. (8) Values of 154 for AHf (CH3CH=N+HZ and CH3N+H=CHz reported by B. H. Solka and M. E. Russell, J. Phys. Chem., 78, 1268 (1974). (9) Values obtained from the proton affinities of NH3 and &CHzNH (207 and 220 kcal mol-l, respectively): I . The values for the heais of foimation of protonated vinyiamine and protonated vinyl alcohol were obtained by estimating the heats of formation and the proton affinities of the unprotonated species. The former were deduced using a group equivalent method and are in satisfactory agreement with the values found by calculations: L. Radom, W. J. Hehre, and J. A. Pople, J. Am. Chem. Soc., 93, 289 (1971). The proton affinities were taken to be the same as those measured for the corresponding saturated analogues, ethylamine and ethanol, respectively. G. Glockler, J. Phys. Chem., 61, 31 (1957).Abstract: The C7H7+ fragment ions formed in toluene, and the chlorinated, brominated, and iodinated toluenes, as well as the C,H6F+ fragment ions in fluorinated toluenes have been studied in an ion cyclotron resonance spectrometer. In all these systems, it is seen that there are two populations of C7H7+ ions, one of which reacts with the parent compound and other compounds, and one of which is totally unreactive. Because the reactive C7H7+ ions from the different precursors all undergo the same reactions and at the same rate as the C7H7+ ions in toluene and benzyl chloride, which have previously been shown to have the benzyl structure, this structure is assigned to the reactive C7H7+ populations; the unreactive C,H,+ ions are assigned the tropylium structure. The relative abundance of the unreactive tropylium ion is low ( < I 5%) in the chloro-, bromo-, and iodotoluenes, and decreases with decreasing energy of the ionizing electrons. This is interpreted to mean that the rearrangement to the seven-membered ring structure occurs after the fragment ion is formed. In toluene and fluorotoluenes, the unreactive component comprises 30-60% of the C7H6X' (X = H, F) ions, and decreases with increasing energy of the ionizing electrons, indicating that rearrangement occurs prior to the fragmentation of the parent ion. Rate constants for the hydride transfer to the benzyl ion from cyclopentane, cyclohexane, 3-methylpentane, and 3-methylhexane are reported. An estimate that LHr

A novel technique for measurement of thermal rate constants and temperature dependences of dissociative recombination: CO2+, CF3+, N2O+, C7H8+, C7H7+, C6H6+, C6H5+, C5H6+, C4H4+, and C3H3+

“…We take advantage of the fact that Bz + reacts with C 7 H 8 and Tr + does not. [25][26][27][28] The procedure has been described in detail previously. 25 Briefly, Ar + was injected into a helium buffer and allowed to react with C 7 H 8 .…”

Linear free energy correlations in mass spectrometry

“…Grubb and Meyerson, 22 from a study of the fragmentation of 13 C-and 2 H-labelled C 7 H 7 C ions derived from benzyl derivatives, concluded that the fragmenting ions had the symmetrical tropylium structure rather than the benzyl structure. More recent studies 23,24 of stable C 7 H 7 C ions derived from a variety of derivatives have concluded that both tropylium and benzyl ions are formed. These studies do not provide information on the structures formed at the appearance energy threshold; such information can be obtained for substituted C 7 ions from appearance energy measurements.…”

Theoretical Approach for the Equilibrium Structures and Relative Energies of C7H7+Isomers and the Transition States between o-, m-, and p-Tolyl Cations

“…Earlier studies focused on the structure of C 7 H 7 + products and the kinetics of the unimolecular dissociations. [1][2][3][4][5][6][7][8][9][10][11] Those reactions have been known to have two competing pathways [1][2][3][4][5][6][7][8][9] and the structures of C 7 H 7 + products have been known to be benzyl, tropylium, and tolyl cations. 5,6,[10][11][12][13] The widely accepted two channel mechanisms include direct C-X bond cleavage channel I leading to the formation of the tolyl ions and lower energy barrier channel II which leads to the formation of either the benzyl cations or tropylium cations or both.…”

“…[1][2][3][4][5][6][7][8][9][10][11] Those reactions have been known to have two competing pathways [1][2][3][4][5][6][7][8][9] and the structures of C 7 H 7 + products have been known to be benzyl, tropylium, and tolyl cations. 5,6,[10][11][12][13] The widely accepted two channel mechanisms include direct C-X bond cleavage channel I leading to the formation of the tolyl ions and lower energy barrier channel II which leads to the formation of either the benzyl cations or tropylium cations or both. [1][2][3][4][5][6][7][8] However, the energetics and mechanisms of the structural rearrangements of C 7 H 7 + product ions following the formation of the ions have not been well established, [10][11][12][13] which has made it difficult to draw well-establish picture of the two-channel mechanisms even with such extensive experimental studies.…”

“…5,6,[10][11][12][13] The widely accepted two channel mechanisms include direct C-X bond cleavage channel I leading to the formation of the tolyl ions and lower energy barrier channel II which leads to the formation of either the benzyl cations or tropylium cations or both. [1][2][3][4][5][6][7][8] However, the energetics and mechanisms of the structural rearrangements of C 7 H 7 + product ions following the formation of the ions have not been well established, [10][11][12][13] which has made it difficult to draw well-establish picture of the two-channel mechanisms even with such extensive experimental studies. Most recently, the structure of C 7 H 7 + ion from channel II was identified as the benzyl cation from the product-resolved spectroscopy following the energy-selective photodissociation of bromotoluene radical cations.…”