Magnetic Resonance in Chemistry

Kläui, Wolfgang; Liedtke, Norbert; Peters, Wilfried

doi: 10.1002/(SICI)1097-458X(199912)37:12<867::AID-MRC550>3.0.CO;2-Apmid: N/A

Indium complexes [LOMeInTp][InCl4] (4) and [LOMeInTp][PF6] (5) containing the tripodal nitrogen ligand Tp− {Tp− = hydrotris(pyrazol‐1‐yl)borate, [HB(pz)3]−} and the tripodal oxygen ligand LOMe− (LOMe− = (cyclopentadienyl)tris(dimethylphosphito‐P)cobaltate(1−), [η5‐(C5H5)CoP(O)R23]−) were synthesized in high yields. Compounds 4 and 5 are the first complexes with a fac‐N3O3 coordination bearing both Kläui's and Trofimenko's tripodal ligands. Their structure in solution was determined unambiguously by 2D 1H NOESY NMR spectroscopy. Copyright © 1999 John Wiley & Sons, Ltd.

Pilawa, Barbara; Więckowski, Andrzej B.; Lewandowski, Marek

doi: 10.1002/(SICI)1097-458X(199912)37:12<871::AID-MRC566>3.0.CO;2-8pmid: N/A

The complex lineshape of the X‐band EPR spectra of natural coal heated at 300–650 °C was numerically analysed. The experimental spectra were approximated by superpositions of one Gauss and three Lorentz lines. Linewidths (ΔHpp), g‐factors and abundances of the components of the total spectrum were evaluated. The total concentration and concentrations of the four types of paramagnetic centres in the coal samples were determined. Two groups of unpaired electrons with strong dipolar interactions responsible for broad Gauss (ΔHpp = 0.68–0.92 mT) and broad Lorentz (ΔHpp = 0.54–0.64 mT) EPR components and two groups of unpaired electrons with exchange narrowed Lorentz lines (ΔHpp = 0.17–0.24 and 0.06–0.08 mT) were detected. Dipolar interactions of unpaired electrons with broad lines changed considerably during the thermal decomposition of coal. A strong influence of atmospheric oxygen molecules on magnetic interactions of unpaired electrons with the broad Gauss and the two narrow Lorentz lines was observed. Copyright © 1999 John Wiley & Sons, Ltd.

Latosińska, Jolanta N.; Seliger, Janez; Nogaj, Boleslaw

doi: 10.1002/(SICI)1097-458X(199912)37:12<878::AID-MRC583>3.0.CO;2-Vpmid: N/A

An NMR–NQR spectroscopic study of three 2‐nitroimidazole derivatives was performed, prompted by the prospective medical applications of these compounds. A comparison of the NMR–NQR spectra of the derivatives taken at 193 and 296 K was made. Moreover, the electronic structure of each derivative was referred to that of pure imidazole, which was possible on the basis of analysis of the bond populations. The effect of substitution of the imidazole ring at the 1 H position was analysed. Copyright © 1999 John Wiley & Sons, Ltd.

Latosińska, J. N.; Seliger, J.; Grechishkin, V. S.; Spychala, J.

doi: 10.1002/(SICI)1097-458X(199912)37:12<881::AID-MRC582>3.0.CO;2-Hpmid: N/A

Results concerning the electronic structure of five cytosine derivatives obtained by the NMR‐ NQR double resonance technique on nitrogen nuclei are reported. NMR‐ NQR spectra of the five cytosine derivatives were taken at 120 K. The influence of substitution at the 4‐N position of the cytosine ring was analysed by NMR‐ NQR. According to the results of the study, the amine group, which acts as a π electron acceptor in most molecular systems, in phenylcytosine and naphthylcytosine becomes an electron donor, while the aromatic rings, which usually compensate for electron density changes in cytosine, act as electron acceptors. When the aromatic substituents of 4‐N‐cytosine are separated by a CH2CH2 chain, the density redistribution is reduced. Copyright © 1999 John Wiley & Sons, Ltd.

Pomares, Marta; Grabuleda, Xavier; Jaime, Carlos; Virgili, Albert; Álvarez‐Larena, Ángel; Piniella, Joan F.

doi: 10.1002/(SICI)1097-458X(199912)37:12<885::AID-MRC572>3.0.CO;2-6pmid: N/A

2,2‐Dimethyl‐1‐(1‐naphthyl)propanol was synthesized and the corresponding enantiomers were isolated by chiral HPLC. These enantiomers gave diastereoisomeric carbamates by reaction with (S)‐(−)‐1‐phenylethyliso‐cyanate, which were studied by NMR. The comparison of NMR data and molecular mechanics calculations allowed us to determine the absolute configuration of corresponding alcohols. Finally, x‐ray results were in agreement with the absolute configuration proposed from the NMR spectra. Copyright © 1999 John Wiley & Sons, Ltd.

Patel, P. K.; Hosur, R. V.

doi: 10.1002/(SICI)1097-458X(199912)37:12<891::AID-MRC580>3.0.CO;2-Mpmid: N/A

A new strategy based on the use of the two‐dimensional TOCSY experiment is described for the determination of the stoichiometry of association of strands in multi‐stranded DNA structures. TOCSY spectra are recorded as a function of DNA concentration and the intensities of cross peaks are monitored to estimate the relative changes in the concentrations of the ordered and single‐strand species at different total DNA concentrations. From these the stoichiometry and the association constant can be calculated. The method has been demonstrated on a quadruplex structure formed by the DNA segment d‐AG3T. Copyright © 1999 John Wiley & Sons, Ltd.

Dokalik, Albrecht; Kalchhauser, Hermann; Mikenda, Werner; Schweng, Gerhard

doi: 10.1002/(SICI)1097-458X(199912)37:12<895::AID-MRC581>3.0.CO;2-7pmid: N/A

Correlations between experimentally determined chemical shifts (15N, 13C, 1H in CDCl3 and DMSO solutions) and GIAO‐calculated isotropic shielding constants, δexpt = a + bσcalcd, are reported that were obtained from a series of nitrogen‐containing heterocycles (5‐, 6‐, 5+6‐, 6+6‐ and 6+6+6‐membered rings). Based on HF, MP2 and B3LYP optimized geometries [6–31G(d,p) basis set], GIAO calculations were performed at the HF, BLYP, and B3LYP levels of theory [6–311++G(d,p) basis set]. The performance of theoretical NMR calculations and the resulting eligibility for routine practical use were assessed from correlation coefficients and from standard deviations of the theoretically predicted shifts. Depending on the experimental conditions and on computational levels, linear regressions between experimental and theoretical data resulted in standard deviations of about 6–12 ppm for all nitrogens, 5–8 ppm for aromatic nitrogens, 1–2 ppm for aromatic carbons and 0.1–0.15 ppm for aromatic hydrogens. Several points that influence the accuracy of theoretically predicted chemical shifts are discussed. Copyright © 1999 John Wiley & Sons, Ltd.

Lewin, Anita H.; Burgess, Jason P.; Sun, Guobin; Fudala, Louise D.

doi: 10.1002/(SICI)1097-458X(199912)37:12<903::AID-MRC557>3.0.CO;2-4pmid: N/A

The proton NMR spectra of the isomeric 3α‐ and 3β‐aminotropanes were recorded in aqueous solution over the pH range 2–14 and the resonances of both diamines were completely assigned. The pH dependence of the chemical shifts of the protons α to the amino groups was used to determine which of the amino groups is more basic in each isomer. The conformations of the unprotonated, monoprotonated and diprotonated species were also deduced from the 1H NMR spectra. For both 3‐aminotropane isomers, the tertiary amino group is more basic than the primary amino group, and the chair form with an equatorial N‐methyl group is the minimum energy conformation. Copyright © 1999 John Wiley & Sons, Ltd.

Lemos, Telma L. G.; Costa, Sonia M. O.; Pessoa, Otilia D. L.; Braz‐Filho, R.

doi: 10.1002/(SICI)1097-458X(199912)37:12<908::AID-MRC579>3.0.CO;2-Ipmid: N/A

Conventional one‐dimensional NMR methods and two‐dimensional shift‐correlated NMR experiments (COSY, HMQC, HMBC) were used for 1H and 13C chemical shift assignments of two naphthoquinone dimers tectol and tecomaquinone I isolated from Lippia sidoides. Copyright © 1999 John Wiley & Sons, Ltd.

Ferreira, Amadéo; Bigan, Muriel; Blondeau, Dominique

doi: 10.1002/(SICI)1097-458X(199912)37:12<912::AID-MRC540>3.0.CO;2-Spmid: N/A

The 13C, 31P and 1H NMR spectra of a series of dioxaphosphinopyridines and pyridoazaphosphinines were studied. The interpretation of the chemical shifts of these compounds was based on model compounds and on selective irradiation and two‐dimensional shift correlated NMR techniques. Copyright © 1999 John Wiley & Sons, Ltd.