Thermochemistry and mass spectrometry of aromatic compounds with tertiary alkyl groups

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Eur. J. Mass Spectrom. 1, 353 - 361 (1995)

Thermochemistry and mass spectrometry of aromatic compounds with tertiary alkyl groups

V.V. Takhistov^* and A.D. Misharev
Department of Chemistry, St Petersburg State University, Stary Petershof, 198904 St Petersburg, Russia.
V.M. Orlov
Moscow Institute of Molecular Biology, Moscow, Russia.
D.A. Ponomarev
Faculty of Chemical Engineering, St Petersburg Forest Technical Academy, Institutski 5, 194018 St Petersburg, Russia.
Jürgen Voss^*
Institute of Organic Chemistry, University of Hamburg, MartinLutherKingPlatz 6, D-20146 Hamburg, .

ABSTRACT:

The mass spectra of two series of functional benzene derivatives with tert-butyl substituents in the 4 position (p Me₃CC₆H₄X, X = COCl, COOH, COSH, COSCD₃, CSSMe, CSCMe₃) or in the 3,5 positions 3,5 (Me₃C)₂C₆H₃ X (X = CMe₃, Br, CN, CH₂Cl, CH₂Br, CHO, COCH₃, CONMe₂, CSNMe₂) have been studied. Ionization energies and appearance energies of some fragment ions were measured by photoionization mass spectrometry. The heats of formation of [p Me₃ CC₆H₄C.triplebond.O]⁺ (579 kJ mol ¹) and [p Me₃CC₆H₄C.triplebond.S]⁺ (840 kJ mol^-1) ions have been derived. It was demonstrated that the former ion is 30 kJ mol¹ more stable than the latter one in the framework of isodesmic reactions. Isodesmic reactions were used to prove that the [M - Me]⁺ ions from p Me₃CC₆H₄CSCMe₃ possess the structure [Me₃CC₆H₄C(SH)CH=CH₂]⁺ at the threshold of their formation. The appearance of abundant Me₃C⁺and X⁺ ions from 3,5(Me₃C)₂C₆H₃X is explained by involvement of rearrangement rather than simple bond cleavage processes.

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