Structural and energetics effects in the chemical ionization of halogen-substituted benzenes and toluenes

Abstract

HEI-WUN EEUNG and ALEX 6. HARRISON. Can. J. Chem. 54, 3439 (1976). The HZ, Dz, CH4, and CD4 chemical ionization (CI) mass spectra of XC6H5, C6H5CHzX, and XC6H4CH3 (X = Clr Br, and I) have been determined. For the benzyl halides the dominant ion observed in all CI spectra is the m / q 91 (benzyl) ion formed by loss of HX(DX) from the protonated (deuteronated) molecule. The CI spectra of the isomeric halotoluenes differ substantially from the spectra of the benzyl halides indicating that isomerization to a common (tropylium-like) structure does not occur in CI. In the H2 CI of XC6H4Y (Y = H or CH3) the major fragment ions observed are YC6H5.HC, Yc6H5f, and YC6H4+, with the relative yields depending strongly on the halogen substituent. Neither the YC6H5 .H+ ion, resulting from HX loss from the H3+.XC6H4Y complex, nor the YC6H4+ ion, resulting from HX loss from XC6H4Y .H+, are observed when X = I. On the other hand YC6H5+, resulting from elimination of X. from XC6H4Y.H+, is observed only for X = Br and I. In the CH4 CI of XC6H4Y, in addition to XC6)I4Y.Ht ions, CH3C6H4Y .H+ ions (HX loss from the CH5+.XC6H4Y complex) are observed for X = F and C1, while YC6H5t ions (loss of X'from XC6H4Y.H+) are observed only when X = I. In addition, displacement of I' by C2H5+, and by C3H5+, is observed in the CH4 CI of the iodo-substituted compounds. The dependency of the products observed and their relative yields on the identity of the halogen substituent is discussed in relation to the reaction energetics.

High‐pressure collisional activation mass spectrometry of aromatic halides

“…[C&I+ [C4H31++ CzHz (8) [C,H,]+ 4 [C,H2]++H (9) [C,H,]+ 4 [C,H]++H (10) Reactions (8) [C6H4C1]+ 3 [C,H,]+ + HCI (11) [C,H,Cl]+ + [C,H,]++C,HCI (12) [C,H,CI]+ 4 [C,HzC1]++C2H2…”

Hydrogen migrations in mass spectrometry. VI—the chemical ionization mass spectra of substituted benzoic acids and benzyl alcohols

“…However, for the halogen substituted acids intense fragment ions are observed at mle 77 depending upon the substituent. Pressure variation studies of the H, CI mass spectra of the halobenzoic acids show' that the formation of these products can be explained by the reaction sequence of Scheme 2, involving.the elimination of X ( (8) 120 (6) The CH, CI mass spectra of the substituted benzoic acids are summarized in Table 2 (7). [MX2H5-C021+ (3) m-OH 100 10 11 [M*C,H51+ (6 [M.C,HJ (10).…”

“…[MX2H5-C021+ (3) m-OH 100 10 11 [M*C,H51+ (6 [M.C,HJ (10). [MI' (7 [M.CZHJ+ (5). [MI' (7) p-CI In the CH, CI mass spectra of the iodobenzoic acids the ion signal at mle 122 corresponds to [MH -I]+, a fragmentation observed7 for simpler iodobenzene derivatives, while [C,H6]+ may originate by further loss of CO, from this fragment.…”

“…[MI' (7 [M.CZHJ+ (5). [MI' (7) p-CI In the CH, CI mass spectra of the iodobenzoic acids the ion signal at mle 122 corresponds to [MH -I]+, a fragmentation observed7 for simpler iodobenzene derivatives, while [C,H6]+ may originate by further loss of CO, from this fragment. Tables 3 and 4 show, this is a fragmentation scheme which is common to all the benzyl alcohols studied.…”

Site of protonation in the reaction of gaseous Brønsted acids with halobenzene derivatives

“…The reaction of gaseous Bransted acids with haloaromatic compounds initiates a complex chemistry which depends not only on the protonation exothermicity but also the identity of the halogen and the nature and position of substit~ents. '-~ The general reaction sequence can be described by the series of reactions (1)(2)(3)(4), where [BH]+ is a gaseous Bransted acid and [RC,H,X-H]+* is the initially produced protonated haloaromatic (not necessarily protonated at the halogen) containing a significant fraction of the protonation exothermicity as internal excitation. This internal excitation may be removed by collision with a neutral gas bath molecule; alternatively, the excited ion may fragment by either reaction (3) or (4).…”