The structure of pyrazoles in the solid state: a combined CPMAS, NMR, and crystallographic study.
The structures of six N-unsubstituted pyrazoles, three already known and three newly synthesized, have been studied by a combination of X-ray crystallography, multinuclear NMR (solution and solid state), and density functional theory (DFT) calculations. In those cases where crystal structure and CPMAS NMR were available, the agreement was almost perfect, allowing a prediction of the tautomer (with certitude) and the tetrameric structure (with high probability) in the case of 5-isopropyl-3-phenyl-1H-pyrazole without knowing the X-ray structure. In the case of the 5-(2-benzylphenyl)-3-trifluoromethyl-1H-pyrazole above represented, the DFT calculations at the B3LYP/6-31G level justify the great stability of this tautomer by the presence of an intramolecular N-H...pi interaction, present in solution.
Claramunt
Rosa M
RM
Departamento de Química Organica y Bio-Organica, Facultad de Ciencias, UNED, Senda del Rey 9, E-28040 Madrid, Spain. rclaramunt@ccia.uned.es
Cornago
Pilar
P
Torres
Verónica
V
Pinilla
Elena
E
Torres
M Rosario
MR
Samat
André
A
Lokshin
Vladimir
V
Valés
Magali
M
Elguero
José
J
D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D015394:Molecular Structure; D011720:Pyrazoles / Q000737:chemistry*; D012996:Solutions
D011720:Pyrazoles; D012996:Solutions