Vibrational spectra of pyrazole and deuterium‐substituted analogues

Abstract

Accurate vibrational frequencies are reported for pyrazole and for seven N-and C-deuterated analogues from FT-IR spectra for the vapour phase at room temperature, diluted CCI, solutions and polycrystalline solids and from Raman spectra in aqueous solutions. Several frequencies are reported for fundamentals not previously observed in the vapour phase in particular. Assignments were carried out by performing a normal coordinate analysis for in-plane and out-of-plane modes, using either Urey-Bradley or general valence force fields. Great care was taken to determine a refined force constant set which agrees as far as possible with observed isotopic shifts. A detailed description of all the normal modes and atomic displacements for in-plane modes is given.

Infrared, Raman and NMR spectra, conformational stability, normal coordinate analysis and B3LYP calculations of 5-amino-4-cyano-3-(methylthio)-1H-pyrazole-1-carbothioamide

“…4 a pleasingly high level of agreement was obtained between experimental and simulated 13 C NMR spectra supporting the calculated structural parameters of AMPC's conformer 1. Good agreement is also obtained for experimental and simulated 15 N NMR spectra (data not shown). Of perhaps more interest are the proton spectra shown in Fig.…”

“…11 (the NH 2 (14,15) barriers to internal rotation). The calculated NH 2 rotational barriers are 6584 cm À1 and 10,320 cm À1 for NH 2(14,15) , NH 2 (19,20) respectively.…”

“…Recently amino-pyrazole derivatives were found to be potentially useful in preventing brain-protein aggregation which is the first phase in the development of Alzheimer's disease [10]. The vibrational assignment of pyrazole itself has been investigated; [11][12][13][14][15][16] however, there is little information regarding vibrational spectra and structure of substituted pyrazoles and N-substituted pyrazoles in particular [17,18]. The subject of the present study, 5-amino-4-cyano-3-(methylthio)-1H-pyrazole-1-carbothioamide, (AMPC, C 6 H 7 N 5 S 2 ) has several structural characteristics: it contains linear AC"N (sp), planar ANH 2 (sp 2 ) along with tetrahedral ACH 3 (sp 3 ) moieties in addition to the pyrazole ring.…”

Vibrational Spectra of Water Solutions of Azoles from QM/MM Calculations: Effects of Solvation

“…In these cases the interpretation of the IR and Raman data can be carried out unambiguously and lead to the estimation of the effects of the solvent environment on the solute geometrical and electronic properties. 3,6,7 Unfortunately most studies do not show some bands very sensitive to the water environment, such as the NH stretching, because in the same region strong solvent absorptions are measured. In the present work we apply quantum chemistry and Ab Initio Molecular Dynamics (AIMD) methods to investigate the solvation effect on the vibrational properties of a prototype of azole, pyrazole, (see Figure 1a), a system already investigated by some of us through a combined X-Ray diffraction and classical molecular dynamics (MD) study.…”

Infrared, Raman and NMR spectra, conformational stability, normal coordinate analysis and B3LYP calculations of 5-Amino-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde

“…Recently amino-pyrazole derivatives were found to be potentially useful in preventing protein aggregation which in the human brain is the first phase of Alzheimer's disease development [9]. The vibrational spectra of pyrazole have been thoroughly investigated [10][11][12], however, there is relatively little information regarding substituted pyrazoles, and N-substituted pyrazoles in particular [13,14]. The inclusion of a substituent group in pyrazole leads to the variation of charge distribution in molecules and consequently this affects the structural, electronic and vibrational parameters.…”