Barbara Nowak-Wydra

UV, 1H and 13C NMR spectra, and AM1 studies of protonation of aminopyridines

Abstract The effect of single and double protonation on the UV, 1 H and 13 C NMR spectra of 2-, 3-, and 4-aminopyridines and their N -methyl and N,N -dimethyl derivatives has been investigated. All the spectra confirm that aminopyridines in diluted acids form monocations by protonation at the ring nitrogen atom and dications in concentrated acids (e.g. 80% D 2 SO 4 ). The formation of dications decreases in the order: 3 > 4 > 2. Computed values of proton affinity PA(1) ring and PA(2) subst. are in agreement with the above interpretations.

FTIR, NMR and kinetic studies of proton transfer reactions from nitro-substituted diarylmethanes to N-bases with guanidine character

Abstract Deprotonation of bis(2,4-dinitrophenyl)methane (C-acid 1) and 2,4-dinitrophenyl-2,4,6-trinitrophenylmethane (C-acid 2) by 7-methyl-1,5,7-triazabicyclo[4,4,0]dec-5-ene (MTBD) and 1,5,7-triazabicyclo[4,4,0]dec-5-ene (TBD) in acetonitrile has been studied using 1 H and 13 C NMR as well as FT-IR spectroscopy. The 1:1 mixtures of N-bases with C-acids form protonated N-bases and products, for which only one respective structure was found. In the case of deprotonated C-acid 1 a symmetrical charge distribution in the phenyl rings was found, whereas for deprotonated C-acid 2 the charge distribution was asymmetrical. The spectral feature was explained as a strong electrostatic interaction between the product and the protonated N-bases. The kinetics of the proton transfer reaction from C-acid 1 and C-acid 2 to MTBD and TBD in acetonitrile are reported. The activation parameters are discussed in two aspects: the steric effect of the basic centre and the delocalization of charge for the carbanion products.

Multinuclear NMR studies of tris(oxaalkyl) borates and their complexes with some metal cations

Abstract Nuclear magnetic resonance (NMR) of 1 H, 13 C, 11 B and 17 O nuclei has been used for the study of complexation of CoCl 2 , NiCl 2 and CuCl 2 salts with three tris(oxaalkyl) borates. All NMR techniques demonstrated the formation of complexes but the most informative were the 13 C and 17 O NMR measurements. The structures of the complexes formed are discussed in this article.

Chiral recognition of Schiff bases by 15N NMR spectroscopy in the presence of a dirhodium complex. Deuterium isotope effect on 15N chemical shift of the optically active Schiff bases and their dirhodium tetracarboxylate adducts

Optically active Schiff bases, derivatives of ortho‐hydroxyaldehydes and their adducts with dirhodium tetracarboxylate complexes have been studied by 15N NMR spectroscopy. The position of the equilibrium of Schiff bases, as well as their adducts, has been established on the basis of measurements of deuterium isotope effects on 15N chemical shifts. At the equilibrium state, the formation of the adducts with dirhodium complexes shifted the proton‐transfer equilibrium towards the NH‐form. Copyright

Differences in proton–proton coupling constants of N+–CH2–CH2 protons of some betaines, N+–(CH2)2-3–COO−, and their complexes in aqueous solution

Abstract Synthesis and 1 H NMR spectra in D 2 O of 4 betaines and 19 betaine complexes with mineral acids containing 2 or 3 CH 2 groups in the tether, N + –(CH 2 ) n –COO − , n =2,3, and diverse volume of the positively charged groups are reported. In compounds containing three CH 2 groups in the tether and three substituents at the nitrogen atom or α, α′-disubstituted pyridine ring, a characteristic multiplet for an AA′MM′X 2 spin system is observed. This is consistent with preference for trans conformation (68–85%). In the spectra of compounds with two CH 2 groups in the tether or three CH 2 groups and unsubstituted pyridine ring, the multiplet changes to a triplet and gives apparent A 2 X 2 and A 2 M 2 X 2 spectra, respectively, consistent with no significant conformational preference. Both the number of CH 2 groups in tether and the bulkiness of the charged groups are responsible for the observed differences of N + CH 2 multiplicity and reflect changes in conformational preferences. According to the PM3 calculations, in the gas phase a gauche -like conformer is more stable than the trans , but in aqueous solution it is reverse.

15N NMR and FTIR studies of 2,4-dinitroanilines and their salts

Abstract Twenty-two 2,4-dinitroanilines were synthesised and their p K a values were determined. The 2,4-dinitroanilines and their protonated forms were studied by 15 N NMR spectroscopy. The relations between the 15 N NMR chemical shifts and the p K a values of the 2,4-dinitroanilines and their salts were found to be linear. The deprotonation reaction of N -methyl-2,4-dinitroanilines and N -methyl-2,4,6-trinitroaniline by MTBD was successful only for the latter and yielded protonated MTBD molecule and the anion in which the electrons are strongly delocalised. The kinetic parameters of the 2,4-dinitroanilines in reactions with hydroxide ions in mixed solvent DMSO:water (95:5, v/v) were determinated and discussed.

Complete Assignment of 1H and 13C NMR Spectra and Conformational Analysis of Thioamide Cannabinoids

The complete assignment of the 1H and 13C NMR spectra of two carbothioamide‐ substituted meroterpenes is presented. Resonance assignments were achieved by the use of one‐ and two‐ dimensional NMR, NOED, selective decoupling measurements and the deuterium isotope effect on the 13C chemical shifts. Six‐membered ring conformations were determined by analysis of proton spin coupling constants with the aid of spectral simulations in conjunction with molecular mechanics calculations and equations correlating coupling constants and dihedral angles. The anisotropy effect of benzene rings was used for structural assignments.

Differentiation of substituent effects from hydrogen bonding and protonation effects in carbon-13 NMR spectra of pyridine N-oxides

Aromatic 13C chemical shifts are reported for 4-substituted and 3-substituted pyridine N-oxides measured in deuteriochloroform, deuterium oxide, perchloric acid (60% in D2O) and dichloroacetic acid (80% in CDCl3), and also for O-alkylated derivatives in (CD3)SO and D2O. The substituent chemical shift (SCS) data show systematic non-additivity in comparison with monosubstituted benzenes. Data for the position para to the variable substituent were analysed by means of the dual substituent parameter equation. For this position multiple substituent interactions are responsible for the non-additive shifts; interactions have both an inductive (polar) and a resonance component. Hydrogen bonding and protonation effects were differentiated from the substituent effect. It is shown that the relative 13C chemical-shift difference [(Δ3–Δ4)/Δ3] is a measure of the hydrogen bond and protonation effects and is not subject to substituent effects. 3-Dimethylaminopyridine N-oxide is protonated at the dimethylamino group, but 4-dimethylaminopyridine N-oxide at the oxygen.

Multinuclear magnetic resonance studies of fluoronitroanilines

Ten fluoronitroanilines have been synthesized and the 1H, 13C, 15N and, 19F NMR spectra of these compounds have been recorded and fully assigned. Density functional theory(DFT) calculations have been performed for all compounds studied. Experimental and theoretical results are compared and the structure and atom character influence on the accuracy of the calculation discussed. Copyright