Gas-phase (ion cyclotron resonance spectrometric) and solid-state (crystallographic) studies of highly substituted pyrazoles (original) (raw)

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).