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

1976; NRC Research Press; Volume: 54; Issue: 21 Linguagem: Inglês

10.1139/v76-494

1480-3291

Hei‐Wun Leung, Alex G. Harrison,

Inorganic and Organometallic Chemistry

The H 2 , D 2 , CH 4 , and CD 4 chemical ionization (CI) mass spectra of XC 6 H 5 , C 6 H 5 CH 2 X, and XC 6 H 4 CH 3 (X = Cl, 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 H 2 CI of XC 6 H 4 Y (Y = H or CH 3 ) the major fragment ions observed are YC 6 H 5 •H + , [Formula: see text], and YC 6 H 4 + , with the relative yields depending strongly on the halogen substituent. Neither the YC 6 H 5 •H + ion, resulting from HX loss from the H 3 + •XC 6 H 4 Y complex, nor the YC 6 H 4 + ion, resulting from HX loss from XC 6 H 4 Y•H + , are observed when X = I. On the other hand [Formula: see text], resulting from elimination of X• from XC 6 H 4 Y•H + , is observed only for X = Br and I. In the CH 4 CI of XC 6 H 4 Y, in addition to XC 6 H 4 Y•H + ions, CH 3 C 6 H 4 Y•H + ions (HX loss from the CH 5 + •XC 6 H 4 Y complex) are observed for X = F and Cl, while [Formula: see text] ions (loss of X • from XC 6 H 4 Y•H + ) are observed only when X = I. In addition, displacement of I • by C 2 H 5 + , and by C 3 H 5 + , is observed in the CH 4 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.