Positive ions and negative ions fab (fast atom bombardment) mass spectrometry of some bisazolium salts

Significant information on the structure of various bisazolium salts of the type CA₂ (C⁺⁺ 2A^?) were revealed by the study of the FAB spectra of their positive and negative ions. Thus only one spectrum, whatever it consists of the positive or of the negative ions spectrum, enables the identification of the cation C⁺⁺ and of the anion A^?. Moreover, the same information are collected from the CAD spectrum of the adduct ion CA⁺ allowing the identification of such a compound in a mixture.     

A multinuclear NMR study in the solid state and in solution of thallium(I) tris-(pyrazol-1-yl)borates (thallium scorpionates)

The ¹H, ¹³C and ¹⁵N NMR spectroscopic properties of six thallium tris-(pyrazol-1-yl)borates, including a tetrakis derivative, were determined. The results in solution were necessary to understand those, more complicated, in the solid state. A collection of ²⁰⁵Tl-¹⁵N and ²⁰⁵Tl-¹³C couplings was measured in the latter state. Among those, a very large coupling constant (between 194 and 282 Hz) has been measured on the carbon at the position 4 of the pyrazole ring in several compounds and particularly for the cyclobutyl derivative [Tl(Tp^Cbu)]. It has been assigned to a direct interaction of the 4-C-H ? Tl type and related to the X-ray structures, when available.     

The Structure of 1H-Perimidin-2(3H)-one and Its Derivatives in the solid state (x-ray crystallography and CP/MAS 13C-NMR), in solution (13C-NMR), and in the gas phase (mass spectrometry)

The X-ray crystal and molecular structures of 1-methyl- 1H-perimidin-2(3H)-one ( 5b ) and 1,3-dimethyl-1H-perimidin-2(3H)-one ( 6 ) were determined. The crystals are built of piles of dimers faced head-to-head in 5b and of alternating independent head-to-tail molecules in 6 , both along the b axis. Semiempirical calculations at the AM 1 level revealed that the eclipsed conformation of the Me groups with respect to the C?O group, found in the crystals, is the most stable. The lack of planarity of the whole molecules is a consequence of the packing forces since it is not found in the calculations. A comparative NMR study was carried out in solution (¹H and ¹³C) and in the solid state (CP/MAS ¹³C) for 1H-perimidin-2(3H)-one ( 2 ) and 1H-benzimidazol-2(3H)-one ( 3 ) with the conclusion that in both heterocycles the oxo tautomer is the most abundant. The structure in the gas phase was approached by mass spectrometry. In the case of 3 , the oxo tautomer loses CO after ionization, while the oxo form of 2 tautomerizes to the hydroxy form which loses, H₂O after a [1,3]-H shift. AM 1 calculations were carried out on the ground and ionized states of 2 .     

Synthesis and spectroscopic properties of Schiff bases derived from 3-hydroxy-4-pyridinecarboxaldehyde

A series of six new Schiff bases has been prepared by reacting aniline and 4-R-substituted anilines (R=CH₃, OCH₃, Br, Cl, NO₂) with 3-hydroxy-4-pyridinecarboxaldehyde. The ¹H, ¹³C, ¹⁵N and ¹⁷O NMR data of these compounds are used to discuss the tautomerism. ¹⁵N NMR and ¹⁷O NMR chemical shifts established the tautomer existing in solution as the hydroxy/imino. ¹³C CPMAS NMR confirms that the same tautomer is found in the solid state. The stabilities of the tautomeric forms have been approached using density functional calculations (B3LYP/6-31G**) in the gas phase. In all cases the neutral hydroxy/imino with E configuration is more stable than the oxo/enamino form (by ∼22 kJ mol⁻¹) and significantly more stable than the betaine (by ∼75 kJ mol⁻¹).     

Crystal structures of 2-(2-methoxyphenyl) perimidine and its hemihydrate

The crystal structures of the title compound and that of its hemihydrate have been determined. The anhydrous compound is roughly planar due to an intramolecular hydrogen bond (IMHB). The orange color can be related to its planarity and to the greater degree of overlapping between the perimidine and the phenyl group than in the hemihydrate. The yellow hemihydrate is not planar and the water molecule joins through O-HN hydrogen bonds two molecules related by a crystallographic twofold axis. In solution the compound behaves like the anhydrous form.     

The structure of azines derived from C‐formyl‐1H‐imidazoles in solution and in the solid state: tautomerism,configurational and conformational studies

The structures of three azines derived from 2‐formylimidazole, 4(5)‐formylimidazole, and 4(5)‐formyl‐5(4)‐methylimidazole have been determined in solution and in the solid state. Density Functional Theory (DFT) Polarizable Continuum Model (PCM) calculations (geometries, energies, and chemical shifts), NMR [solution and cross polarization magic‐angle spinning (CPMAS)], and X‐ray crystallography [azine of 4(5)‐formylimidazole] have been used. The configuration around the central C = N bonds has been determined and some insights about prototropic tautomerism and conformation have been gained. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of Substituents on the Regioselectivity of the Reaction of α‐Tosyloxyketones with Thioureas in Acidic Medium: Access to 2‐Aminothiazoles and 2‐Imino‐2,3‐dihydrothiazoles

Regioselective condensation of α‐tosyloxyacetophenones 1 and N‐substituted thioureas 2 in acidic medium to give regioisomers 2‐aminothiazoles I and 2‐imino‐2,3‐dihydrothiazoles II is largely influenced by the substituents present on 1 and 2 . A mechanism, supported by DFT calculations has been proposed to explain the observed regioselectively.     

Structure of N,N'-bis(amino acids) in the solid state and in solution. A 13C and 15N CPMAS NMR study

Three bis(amino acids) linked by the amino groups have been prepared and structurally characterized. We have named them Gly-Gly, Ala-Ala and Gly-Ala (or Ala-Gly). These compounds have been characterized by NMR both in solution and in the solid state. They exist as zwitterions with the ammonium group proximal to the carboxylate anion. In the case of Gly-Ala, a dynamic situation is observed by CPMAS NMR ((13)C and (15)N) corresponding to a double proton migration between two proximal tautomers.     

A 1H, 13C and 15N NMR study in solution and in the solid state of six N-substituted pyrazoles and indazoles

Three N-substituted pyrazoles and three N-substituted indazoles [1-(4-nitrophenyl)-3,5-dimethylpyrazole (1), 1-(2,4-dinitrophenyl)-3,5-dimethylpyrazole (2), 1-tosyl-pyrazole (3), 1-p-chlorobenzoylindazole (4), 1-tosylinda-zole (5) and 2-(2-hydroxy-2-phenylethyl)-indazole (6)] have been studied by NMR spectroscopy in solution (1H, 13C, 15N) and in the solid state (13C, 15N). The chemical shifts have been compared with GIAO/DFT calculated absolute shieldings. Some discrepancies have been analyzed.