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.     

Functionalization of Reduced Graphite Oxide Sheets with a Zwitterionic Surfactant

Films of a few layers in thickness of reduced graphite oxide (RGO) sheets functionalized by the zwitterionic surfactant N‐dodecyl‐N,N‐dimethyl‐3‐ammonio‐1‐propanesulfonate (DDPS) are obtained by using the Langmuir–Blodgett method. The quality of the RGO sheets is checked by analyzing the degrees of reduction and defect repair by means of X‐ray photoelectron spectroscopy, atomic force microscopy (AFM), field‐emission scanning electron microscopy (SEM), micro‐Raman spectroscopy, and electrical conductivity measurements. A modified Hummers method is used to obtain highly oxidized graphite oxide (GO) together with a centrifugation‐based method to improve the quality of GO. The GO samples are reduced by hydrazine or vitamin C. Functionalization of RGO with the zwitterionic surfactant improves the degrees of reduction and defect repair of the two reducing agents and significantly increases the electrical conductivity of paperlike films compared with those prepared from unfunctionalized RGO.     

A conformational study of bis-, tris- and tetrakis-pyrazolylmethane. Crystallography, L.S.R., dipole moments and theoretical calculations

Theoretical calculations (MM2 and MNDO) have been carried out on several conformations of bis-, tris- and tetrakispyrazolylmethane. The potential surface thus obtained has been compared with experimental results both in solution (lanthanide shift reagents, dipole moments) and in the solid state (crystallography). The structure of tetrakispyrazolylmethane (3) was determined by X-ray diffraction. The compound crystallizes in the C2/c space group, with a cell of dimensions 29.5117(14), 6.9815(2), 13.8903(4) Å and 105.237(3)°. The molecule presents an approximate S₄( ) axis such as N12, N22, N32 and N42 form a distorted tetrahedron. The calculated conformations of minimum energy are consistent with dielectric measurements. The structure of 3 in the solid state lies 5.0 kcal.mol-1 above the minimum as a result of the crystal field. To explain the LSR results, a coordination with two pyrazole nuclei has to be assumed. The presence of a metal (LSR, organometallic complexes) strongly modifies the conformation: in these conditions, bidentated and tridentated structures are observed.     

Systèmes aromatiques à 10 électrons π dérivés de l'aza-3a penlalène. VIII. Recherches dans la série du pyrazolo[3,2-c]-s-triazole

It has been shown that the reaction of β-ketoesters with 1,2-diamino-1,3,4-triazoles affords pyrazolo[3,2-c]-s-triazoles. These results induces us to propose a 7,8-dihydro-9H-s-triazolo[4,3–6]-[1,2,4] triazepin-8-one structure for the intermediate in this synthesis.     

Host-guest chemistry. 2. Amine inclusion compounds of 2-[o-(triphenylphosphoranylidenamino)benzyliden]amino-1H-2,3-dihydroindazol-3-one. X-ray structure of its 1∶1∶1 inclusion complex with isopropylamine and water

The crystal and molecular structure is reported for the inclusion compound 2-[o-(triphenylphosphoranylidenamino)benzyliden]amino-1H-2,3-dihydroindazol-3-one/isopropylamine/water3b. The crystal structure consists of discrete dimeric salt-like aggregates joined together by strong N⁺–H...^–O–C hydrogen bonds between pairs of centrosymmetrically-related indazolonate anions and isopropylammonium cations. Six other inclusion compounds have been prepared and characterized by NMR [with propylamine (3a), withtert-butylamine (3c), withsec-butylamine (3d), withtert-pentylamine (3e), with 1-methylbutylamine (3f) and withiso-pentylamine (3g)]. Two different arrangements are found, both with the host being in the anionic form. The guests are either: (i) one protonated amine and one water molecule (3b and3f); or (ii) one protonated amine and the corresponding neutral amine (3a, 3c, 3d, 3e and3g). Supplementary Data relating to this article (structure factors, thermal components, hydrogen parameters and bond distances and angles, and¹³C-NMR shifts) are deposited with the British Library at Boston Spa, Wetherby, West Yorkshire, U.K., as Supplementary Publication No. SUP 82155 (23 pages).For Part 1, see Reference [1].     

A theoretical NMR study of polymorphism in crystal structures of azoles and benzazoles

The NMR chemical shifts of two azoles and one benzazole whose crystal structures present polymorphism have been computed using the GIPAW approach. ¹⁵N and ¹³C nuclei have been studied. Statistical analysis of the computed ¹³C and ¹⁵N chemical shifts indicates that the GIPAW chemical shifts reproduce with a high degree of accuracy those experimentally reported. This methodology can be used to identify other polymorphic crystal structures.     

Energetic studies of urea derivatives: Standard molar enthalpy of formation of 3,4,4′-trichlorocarbanilide

Thermochemical and thermophysical studies have been carried out for crystalline 3,4,4′-trichlorocarbanilide. The standard (p° = 0.1 MPa) molar enthalpy of formation, at T = 298.15 K, for the crystalline 3,4,4′-trichlorocarbanilide (TCC) was experimentally determined using rotating-bomb combustion calorimetry, as ?(234.6 ± 8.3) kJ · mol^?1. The standard enthalpy of sublimation, at the reference temperature of 298.15 K, was measured by the vacuum drop microcalorimetric technique, using a High Temperature Calvet Microcalorimeter as (182.1 ± 1.7) kJ · mol^?1. These two thermochemical parameters yielded the standard molar enthalpy of formation of the studied compound, in the gaseous phase, at T = 298.15 K, as ?(52.5 ± 8.5) kJ · mol^?1. This parameter was also calculated by computational thermochemistry at M05-2X/6-311++G7 and B3LYP/6-311++G(3df, 2p) levels, with a deviation less than 4.5 kJ · mol^?1 from experimental value. Moreover, the thermophysical study was made by differential scanning calorimetry, DSC, over the temperature interval between T = 263 K and its onset fusion temperature, T = (527.5 ± 0.4) K. A solid–solid phase transition was found at T = (428 ± 1) K, with the enthalpy of transition of (6.1 ± 0.1) kJ · mol^?1. The X-ray crystal structure of TCC was determined and the three-centred N–H?OC hydrogen bonds present analyzed.     

The structure of ammonium pyrazolates in the solid state

The crystals obtained by mixing equimolar amounts of diethyl 1H-pyrazole-3,5-dicarboxylate and the primary amines phenethylamine and homoveratrylamine are ammonium pyrazolate salts as determined by 13C and 15N CPMAS NMR.     

Molecular recognition: improved binding of biotin derivatives with synthetic receptors

NMR titrations and Monte Carlo conformational searches have been used to study the molecular recognition features of five urea derivatives with two synthetic hosts. We have improved the binding constant (Kb) values for all the studied guests and measured the largest binding constant of a complex involving a biotin derivative (biotin methyl ester) bound to a synthetic host by means of several interaction points and not only through the urea moiety.     

Host-guest chemistry of tolbutamide

The molecular recognition features of tolbutamide with four synthetic hosts have been studied by means of NMR titrations, NOESY experiments and Monte Carlo (MC) conformational search. The interaction strength and the most probable structure reveal new insights on the recognition phenomena of this urea derivative in comparison with close related compounds.