Magnetic Resonance in Chemistry

Hydrogen bond between the OH group and the fluorine atom is not involved in the ^1hJ_FH spin-spin coupling transmission in 2-fluorophenol. This is typical of a Fermi contact term transmitted mainly through exchange interactions owing to the overlap of proximate electronic clouds.

¹H and ¹³C NMR chemical shift predictions of spiro-homo- and methano[60]fullerenes containing chiral centers in attached fragment were made using the two-dimensional NMR technique (HH COSY, ¹H–¹³C HSQC and HMBC) and the quantum chemistry GIAO calculation method in the PBE/3z approach. The resonances of the fullerene carbons in α-, β- and δ-positions relative to the position of the substituent exhibit the greatest diastereotopic splitting.

The structure of a nitrogen-rich segment in a fulvic acid from Antarctica was studied using ¹³C{¹⁴N} and ¹⁵N solid-state NMR with dipolar dephasing. Analysis of ¹⁵N and ¹³C chemical-shift trends in seven model compounds and literature data rules out assignment of the unusual peaks in the fulvic-acid spectra to guanidinium, as found in arginine, and shows instead that the five-membered hydantoin ring provides a good match.

F₁-selective HSQC–Relay_n–COSY, highly folded HSQC–TOCSY, F₁-selective F₁-decoupled TOCSY–ROESY are proposed as routinely usable pulse sequences for the easy analysis of complex oligosaccharides.

The efficiency of the 1H-15N CP transfer under fast MAS on several labelled and unlabelled organic chemical compounds is investigated. It is shown experimentally that the adiabatic sequence gives a much higher level –a gain factor up to 3.5 at a MAS frequency of 30 kHz- than the more conventional RAMP sequence. It renders possible the detection of non protonated nitrogen atoms at natural abundance with 2.5-mm external diameter rotors on a 9.4 T spectrometer.

A novel derivative of 2-phenylpyrazolo[1,5-a]pyrimidineacetamide (DPA-713, which is known to display a good targeting capability toward peripheral benzodiazepine receptors), bearing a [¹³C]butynoate moiety has been synthesized and tested for para-hydrogenation as a potential hyperpolarized probe for ¹³C-MRI. Para-Hydrogen Induced Polarization effects have been detected in both ¹H and ¹³C-NMR spectra of the corresponding alkene, and a ¹³C-MR image has been acquired.

Limitations of the homonuclear DQ recoupling sequence BaBa in studies of ³¹P-³¹P spatial proximities in Pd-phosphine complexes were explored under the conditions of fast MAS. Effects of internuclear distances, isotropic chemical shift and chemical shift anisotropy (CSA) offsets on the detectibility of SQ-DQ correlations were examined. Correlations up to 4.6 Å could be obtained even in four-spin systems. CSA values up to 270 ppm are well tolerated; however, for isotropic chemical shift offsets larger than 50 ppm, the intensity of DQ coherences is too small.

This letter illustrates the potency of diffusion-ordered spectroscopy experiments for solving problems in ring-closing metathesis chemistry, such as the discrimination between cyclomonomer and cyclodimer formation from β-lactam precursors.

A series of novel biscyclometalated iridium (III) complexes with an ancillary disulfonated bathophenanthroline (DSBP²⁻) ligand, Ir(L)₂DSBPNa, L = 2−phenylpyridine (ppy), 2,4−difluorophenylpyridine (fppy), and 1−phenylisoquinoline (piq), were found to have two isomeric forms. The chemical structures of the isomers were determined by the oneand two-dimensional ¹H and ¹³C NMR studies. The isomerization was proved to be originated from the disulfonaterelated regio-isomer of the DSBP²⁻ ligand.

Regioselective synthesis and complete structural assignments of 1,4-disubstituted 1,2,3-triazole derivatives by using 1D and 2D NMR spectral techniques (DQF COSY, HETCOR and HMBC).

A series of N-arylsulfonyl-t(3)-iso- propyl-r(2),c(6)-diarylpiperidin-4-ones 1– 8 were synthesized and the preferred conformation of aryl sulfonyl group at nitrogen and isopropyl group at C– 3 was determined by spectral and theoretical studies.