Gas-phase (ion cyclotron resonance spectrometric) and solid-state (crystallographic) studies of highly substituted pyrazoles
✍ Scribed by Jose-Luis M. Abboud; Concepcion Foces-Foces; Marta Herreros; Hamid Homan; Lourdes Infantes; Rafael Notario; Adolf W. Krebs; Jörg Neubauer; José Elguero; Nadine Jagerovic
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 536 KB
- Volume
- 9
- Category
- Article
- ISSN
- 0894-3230
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✦ Synopsis
The gas-phase basicities of 3,4,5-tri-tert-butylpyrazole (I) and 1,3,4,5-tetra-tert-butyl-pyrazole (11) were measured by Fourier transform ion cyclotron resonance spectrometry. The x-ray molecular structures of 1-HCI (a monohydrate) and I1 were determined. A clear lack of planarity is present in the pyrazole rings because of the steric effects of the tert-butyl substituents. The CSp3 atom bonded to N-1, 12-3, C-4 and C-5 atoms deviates significantly from the pyrazole plane, as expected on the basis of semi-empirical AM1 calculations. In I-HCI, the molecules form dimers through symmetry centres in which the chlorine atom and the water molecules play an important role.
The proton affinity ( P A ) is defined as
GBs were determined from equilibrium protontransfer reactions conducted in a modified Bruker CMS-47 Fourier transform ion cyclotron resonance (FT- ICR)' mass spectrometer used in previous studies." Its high magnetic field strength (4.7 T) easily allows the PA (B) = AHH + (g).