Magnetic Resonance in Chemistry

Azaroual‐Bellanger, Nathalie; Perly, Bruno

doi: 10.1002/mrc.1260320103pmid: N/A

Deuterium NMR and relaxation data are presented to investigate the state of β‐cyclodextrin in aqueous solution and to derive dynamic parameters for inclusion complexes. Labelled host and guest molecules were used, and dedicated pulse sequences are proposed for improving the deuterium spectra in terms of reduction of artifacts and of solvent peak(s) and also in terms of total duration of the experiments. This technique was used to investigate the state of β‐cyclodextrin in aqueous solution and to derive important information regarding the degree of dynamic coupling between host and guest in inclusion complexes.

Schröder, Harald; Haslinger, Ernst

doi: 10.1002/mrc.1260320104pmid: N/A

In H,H COSY spectra of rigid cyclic terpenes, many long‐range couplings can be observed. The coupled nuclei are connected either by a zig‐zag coupling path or they are close in space. The latter are called ‘through‐space’ coupling. A certain stereospecific relationship between the coupling partners is necessary. This phenomenon is in accordance with the theoretical explanations.

Stepanov, Alexander G.; Maryasov, Alexander G.; Romannikov, Vyacheslav N.; Zamaraev, Kirill I.

doi: 10.1002/mrc.1260320105pmid: N/A

The molecular mobility and dehydration reaction of tert‐butyl alcohol, selectively deuteriated in the methyl groups (t‐BuOH(2 – 2H9), dTBA), absorbed on H‐ZSM‐5 zeolite was studied using 2H NMR spectroscopy. At 173–298 K two modes of fast anisotropic motion were observed for the adsorbed alcohol: rotation of CD3 groups around the CC bonds and rotation of the entire (CD3)3C fragment around the CO bond. The influence of the walls of the H‐ZSM‐5 channels on the geometry of adsorbed dTBA is small, the increase in the CD3CO angle not exceeding 2.7 ± 1.2° compared with the same angle in solid dTBA. This is explained by location of the alcohol molecules at channel intersections of the zeolite, whose dimensions exceed those of the dTBA molecule. The lifetime of the dTBA molecule at these adsorption sites exceeds 1 × 10−5 s. The observed reaction products are deuteriated water with an unusual 2H NMR lineshape and two types of butene oligomers: less mobile species with the lineshape typical of solid‐state 2H NMR and more mobile species with a liquid‐like lineshape. The number of more mobile species increases with increase in temperature. In addition, 2H NMR indicates the presence of tert‐butyl groups in the reaction products. For oligomers with a liquid‐like lineshape, the diffusion coefficient D is 3 × 10−13 m2 s−1 at 373 K, whereas for oligomers with a solid‐like lineshape D ≪ 5 × 10−14 m2 s−1 at 173‐373 K. The diffusion coefficient for the t‐BuOH molecule was estimated as D ≪ 2 × 10−14 m2 s−1 within the temperature range 173–296 K.

Hepp, M. A.; Man, P. P.; Trokiner, A.; Fraissard, J.

doi: 10.1002/mrc.1260320106pmid: N/A

NMR nutation and quadrupole echo experiments were used to determine the quadrupole frequency (ωQ) of 87Rb (I = 3/2) in a single crystal of RbCaF3. Since RbCaF3 has a cubic unit cell above 195 K, there is no second‐order quadrupole shift and the spectrum is rather featureless. By fitting the response of 87Rb, as a function of pulse duration, to the predicted response we were able to determine that the average ωQ/2π = 4.5 kHz in this sample. Discrepancies in the agreement between the theory and the experiment for the echo response were attributed to differential relaxation of the central and satellite transitions.

Kilpeläinen, Ilkka; Kaltia, Seppo; Kuronen, Pirjo; Hyvärinen, Kristiina; Hynninen, Paavo H.

doi: 10.1002/mrc.1260320107pmid: N/A

The 1H and 13C NMR spectra of 132(R)‐methoxychlorophyll a were assigned utilizing the two‐dimensional 1H‐detected heteronuclear one‐bond (HMQC) and multiple‐bond (HMBC) correlation techniques. The protons and carbons of the macrocycle and its short side‐chains could be completely assigned using the HMQC and HMBC data in concert. These techniques were also valuable in achieving assignments for the phytyl chain, which were previously incomplete. The proton and carbon assignments of the P1‐CH2, P2‐CH, P4‐CH2 and P15‐CH groups and those of all methyl groups of the phytyl chain could be established by the coupling patterns and by the combined information obtained from the HMQC and HMBC connectivities. Fairly unambiguous proton and carbon assignments were also obtained for the P6‐CH2, P7‐CH, P9‐CH2, P11‐CH and P14‐CH2 groups. The sensitivity of the HMQC and HMBC techniques is good, making it possible to achieve the spectral assignments under high dilution and monomeric conditions. This was considered to be of paramount importance in the structural analysis of chlorophylls and related compounds, which are difficult to prepare in adequate amounts and purity because of their lability and which show a strong aggregation tendency at higher concentrations and lower temperatures.

Zhang, Yong; Li, Lin‐Feng; You, Xiao‐Zeng

doi: 10.1002/mrc.1260320108pmid: N/A

The natural hybrid orbitals of halogen atoms in various halogen‐substituted alkanes and benzenes have been calculated by the Fenske–Hall MO SCF method and natural hybrid orbital theory. Four consistent parameters i, s, d and π are derived to describe the nuclear quadrupole coupling constant (QCC) of the halogen isotopes 35Cl, 81Br and 127I, with modification by the asymmetry parameter η. A semi‐empirical expression is proposed from a different point of view.

Baudrillard, Vincent; Davoust, Daniel; Ple, Gerard

doi: 10.1002/mrc.1260320109pmid: N/A

The 1H, 13C and 29Si NMR spectral characteristics of β‐silylated silyl enol ethers were determined. nJ(Si, H) measurements (2 < n < 4) were achieved from selective polarization transfer experiments with selective decoupling during acquisition. 1H,29Si two‐dimensional heteronuclear correlation confirmed the positions of the silylated groups in the molecules.

Cerioni, Giovanni; Giumanini, Angelo G.; Verardo, Giancarlo; Dahn, Hans

doi: 10.1002/mrc.1260320110pmid: N/A

Natural abundance 17O NMR data for seven aliphatic, nine cyclic and thirteen aromatic N‐nitrosamines, recorded at room temperature in acetonitrile, are reported. Differences in chemical shifts among and within the three groups are discussed in terms of electronic and steric effects. The σ+ value for the N‐nitrosamine group was estimated. A comparison between amides and N‐nitrosamines was made.