Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1260241201pmid: N/A

Saunders, John K.; Stevens, John D.

doi: 10.1002/mrc.1260241202pmid: N/A

A simple procedure to simplify the 2D‐COSY spectra of molecules in which significant T1 variations occur is described. The procedure was applied to distinguish between the methine and methylene protons of the reducing sugar L‐idose.

Babushkina, T. A.; Koreneva, L. G.; Zolin, V. F.

doi: 10.1002/mrc.1260241203pmid: N/A

The structure of a lanthanide porphyrin complex was reinvestigated using a new treatment for the paramagnetic NMR shifts. It was found to differ from that obtained previously in that the ion was closer to the macrocyclic ligand. The new treatment is based on ab initio estimation of the coefficients describing the anisotropy of magnetic susceptibility, proportional to the pseudo‐contact shifts. These coefficients were estimated using an electrostatic model of the complex; the ‘extra’ ligand (β‐diketonate) was taken into account and shown to be essential. The NMR spectrum of a non‐axial complex under conditions of restricted rotation of the ‘extra’ ligand is described.

Wasylishen, Roderick E.; de P. Nicholas, A. Martin

doi: 10.1002/mrc.1260241204pmid: N/A

Nitrogen‐14 and oxygen‐17 NMR spin‐lattice relaxation measurements on nitrous oxide yield a 17O nuclear quadrupolar coupling constant of 12.4 ± 1.2 MHz. This result compares well with the value of 12.7 MHz obtained by scaling the value calculated using ab initio molecular orbital theory at the 6–31G* level.

Gerothanassis, Ioannis P.; Lauterwein, Jürgen

doi: 10.1002/mrc.1260241205pmid: N/A

Several referencing techniques for measuring 17O NMR chemical shifts in diamagnetic and paramagnetic solutions have been examined. 1,4‐Dioxane is recommended as an external reference standard for diamagnetic solutions because the 17O resonance position is independent of temperature between 27 and 90°C. At 40°C the 17O chemical shift, within experimental error, corresponds to that of doubly distilled water. Nitromethane cannot be considered as a suitable internal reference because of large solvent effects on the 17O chemical shift. Further, in organic solutions its lanthanide‐induced chemical shifts are not negligible. For the study of paramagnetic solutions the combined use of a cylindrical and a spherical cell is proposed: the 17O resonance of either the magnetically active solvent or a convenient compound added to the solution is recorded in both cells; the chemical shift difference between the two measurements is the bulk magnetic susceptibility shift.

Musmar, M. J.; Zektzer, Andrew S.; Martin, Gary E.; Gampe Jr., Robert T.; Lee, Milton L.; Tedjamulia, Marvin L.; Castle, Raymond N.; Hurd, Ralph E.

doi: 10.1002/mrc.1260241206pmid: N/A

Two‐dimensional heteronuclear chemical shift correlation, heteronuclear relayed coherence transfer and autocorrelated 13C—13C double quantum coherence have been used to assign the proton and 13C NMR spectra of benzo[b]phenanthro[4,3‐d]thiophene. The highly complementary nature of the heteronuclear relay and carbon–carbon double quantum spectra conveniently provides the means of avoiding breaks in the carbon–carbon connectivity network assembled by the latter, which may arise when strongly AB rather than AX carbon–carbon pairings are encountered. Nuclear Overhauser difference spectra have shown the title compound to possess a tertiary helical structure similar to that of phenanthro[3,4‐b]thiophene; the average separation between the H‐1 and H‐13 atoms of the title compound was found to be 2.06 ± 0.04 Å.

Choe, Jong‐In; Choi, Hyung‐Soo; Kuczkowski, Robert L.

doi: 10.1002/mrc.1260241207pmid: N/A

The proton NMR spectra of four deuteriated species of propylene ozonide and five of ethylene ozonide were analysed. The deuterium isotope shifts were 0.0140 ppm (H gem to D), 0.0034 ppm (H trans to D) and 0.0015 ppm (H cis to D) for propylene ozonide. The same trends were observed in ethylene ozonide. The isotope shifts were not additive when two geminal protons were substituted by deuterium. The relative intensities of microwave rotational and proton NMR transitions were compared for propylen ozonide‐d1 prepared stereoselectively in order to assign unambiguously its chemical shifts and spin–spin splittings.

Uusvuori, Raimo; Lounasmaa, Mauri

doi: 10.1002/mrc.1260241208pmid: N/A

Models for isotropic, axially symmetric and fully anisotropic overall rotational diffusion with single diffusional or three‐state internal motion are reviewed or derived and applied to 13C spin‐lattice relaxation data for the N‐methyl groups of tropine and pseudotropine. The results are compared. Complete equations containing the dependence on the equilibrium positions are given for the three‐state jump models. Despite the considerable approximations which these models imply, they are able to predict the expected features of the internal N‐methyl group motion in tropine and pseudotropine: hindered three‐state jumping, which is of the same rate for tropine and pseudotropine and which is moderately independent of concentration and the model for overall motion. Although the nitrogen inversion in these compounds is slow compared with methyl rotation, and does not affect the relaxation, the equations are also derived for double internal motion where the internal rotation axis jumps between two non‐equivalent sites having an arbitrary but fixed orientation within the molecule, and where the innermost internal motion is diffusional or jumpwise as in single internal motion. Some considerations regarding the units of the rotational diffusion constants, errors in T1 measurements, and the reduction of the equations for fully anisotropic overall motion to equations for axially symmetric and, further, for isotropic overall motion are presented.

Crabb, Trevor A.; Roch, Olive G.; Robinson, Paul

doi: 10.1002/mrc.1260241209pmid: N/A

In contrast to the reported reaction between trans‐1‐aminotetralin‐2‐ol and formaldehyde, which gives r‐6a, c‐9a,t‐15a,t‐18a‐5,6,6a,9a,14,15,15a,18a‐octahydro‐9,18‐methanodinaphtho[1,2‐d:1′,2′‐i][1,6,3,8]dioxadiazecine, an examination of the δ 4.0–5.0 region of the 1H NMR spectra of the products of the reaction between trans‐3‐aminotetralin‐2‐ol and formaldehyde showed these to be a 50:50 mixture of r‐5a,t‐8a,c‐14a,t‐17a‐ and r‐5a,c‐8a,t‐14a,t‐17a‐5,5a,8a,9,14,14a,17a,18‐octahydro‐8,17‐methanodinaphtho[2,3‐d:2′,3′‐i] [1,6,3,8]dioxa‐diazecine. In a similar way, the reaction between trans‐2‐aminocyclohexanol and formaldehyde was re‐examined and found to produce initially a ca 80:20 mixture of r‐4a,t‐7a,c‐11a,t‐14a‐ and r‐4a,c‐7a,t‐11a,t‐14a‐7,14‐methanoperhydrodibenzo[d,i][1,6,3,8]dioxandiazecines.

Berger, Stefan; Diehl, Bernd W. K.

doi: 10.1002/mrc.1260241210pmid: N/A

The complete series of all possible benzenes bearing one deuterium atom and one to five methyl groups was synthesized. The deuterium isotope effects on the carbon chemical shifts of the aromatic and aliphatic carbon atoms were measured and shown to obey an empirical increment system. The isotope effects over one bond correlate with the C,H spin coupling constants.