Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1260240901pmid: N/A

Munavalli, S.; Szafraniec, L. L.; Beaudry, W.; Poziomek, E. J.

doi: 10.1002/mrc.1260240902pmid: N/A

The methylene proton chemical shifts of the system appear to be affected by the synergistic interactions of a combination of various effects. Although it is difficult to single out the origin, transmission and magnitude of these effects, the synergistic interactions pervade the molecule, causing a net displacement of the chemical shifts. The substituent‐produced chemical shifts show a clear trend in their dependence on the nature of the substituents and the Hammett parameters. Strong through‐conjugation between the aromatic nitrogen and resonance donor substituents in the para‐position is observed.

Bellama, Jon M.; Nies, J. Dirk; Ben‐Zvi, Nava

doi: 10.1002/mrc.1260240903pmid: N/A

The 1H, 13C and 29Si nuclear magnetic resonance spectra of the parent compound and twelve derivatives of 2,8,9‐trioxa‐5‐aza‐1‐silatricyclo[3.3.3.01,5]undecane (silatrane) are discussed. Effective Taft polarity constants for the silatrane substituents are proposed. An equation is developed to correlate the 29Si NMR chemical shifts of the silatranes with the corresponding organo‐triethoxysilanes.

Espinosa, Antonio; Gallo, Miguel A.; Campos, Joaquín; Entrena, Antonio; Camacho, Encarnación

doi: 10.1002/mrc.1260240904pmid: N/A

The 13C NMR spectra of 24 1,3‐dioxolane derivatives are reported in an attempt to propose parameters for the C‐2, C‐4 and C‐5 shifts from the 2‐Me and 4‐Me substituents, based on the ring stereochemistry. These parameters are obtained from simultaneous equations, and clearly agree with those calculated by the use of pattern molecules. The calculated parameter for the C‐4 shift due to a 2‐Me group differs notably from that proposed by other workers.

Vainiotalo, Anto; Vepsäläinen, Jouko

doi: 10.1002/mrc.1260240905pmid: N/A

The 1H and 13C NMR spectra of 1‐nitroso‐2‐naphthol and its disodium 3,6‐disulphonate, 2‐nitroso‐1‐naphthol and its sodium 4‐sulphonate and the complexes of the sulphonated ligands with dioxouranium(VI) were recorded and analysed. The results show the nitrosonaphthols exist predominantly in the oxime form, and that the 1‐nitroso compounds have a preferred structure. The quinonoid oxygen does not take part in the complexation with dioxouranium(VI), which is effected by chelation through the oxime oxygen and nitrogen.

Swanson, Jon T.; Davis, Larry P.; Dorey, R. Cameron; Carper, W. Robert

doi: 10.1002/mrc.1260240906pmid: N/A

Electron paramagnetic resonance spectroscopy has been used to probe the decomposition pathway of neat molten 2,4,6‐trinitrotoluene (TNT). The analogs of TNT labelled in the 2‐, 2,6‐, 4‐ and 2,4,6‐positions with 15N, and labelled in the α‐, 3,5‐ and α,3,5‐position with 2H have been studied, and their spectra recorded at 240°C. The results indicate that the earliest observable radical produces a spectrum resulting from coupling with a para‐N (aN = 10.8G), five equivalent hydrogens (aH = 2.7G) and two benzylic hydrogens (aH = 10.7G).

Chang, Ching‐Jer; Díaz, Luis E.; Morin, Frederick; Grant, David M.

doi: 10.1002/mrc.1260240907pmid: N/A

Natural abundance 13C NMR spectra of different crystal habits of pure aspirin and several aspirin tablets in the solid state have been measured by using the combined techniques of high‐power decoupling, cross‐polarization and magic angle spinning. Solid‐state NMR of aspirin had excellent sensitivity compared with liquid‐state NMR, and the carbon signals were assigned using a modified pulse sequence to detect non‐protonated carbons. The solid‐state 13C NMR spectra of two crystalline forms of aspirin were identical, suggesting that the origin of their difference is not polymorphic.

Hansen, Poul Erik; Lyčka, Antonín

doi: 10.1002/mrc.1260240908pmid: N/A

Carbon‐carbon coupling constants of 1‐phenylazo‐2‐naphthol and 2‐phenylazo‐1‐naphthol have been measured with the SEMINA‐1 pulse sequence. The carbon–carbon couplings provide an unambiguous assignment of the 13C spectra. The magnitudes of the carbon–carbon coupling constants are discussed in relation to the tautomeric nature of the compound. Substituent effects on couplings are also considered.

Charushin, V. N.; Sorokin, N. N.; Chernyshev, A. I.; Baklykov, V. G.; Ponizovsky, M. G.; Chupakhin, O. N.

doi: 10.1002/mrc.1260240909pmid: N/A

The 1H and 13C NMR spectra of tetrahydroquinoxalines condensed with pyridazine, pyrazine, oxazine, oxadiazine, thiadiazine or triazine rings have been measured in DMSO‐d6 solution. The effects of six‐membered heterocycles on 1H and 13C chemical shifts and the values of one‐bond 1J(CH) and vicinal 3J(HH) coupling constants for the ring junction fragment are considered. The differences between the 1H and 13C spectral parameters of tetrahydroquinoxalines annelated with five‐ or six‐membered heterocycles with the same set of heteroatoms attached to the ring junction carbons are also discussed.

Craik, David J.; Adcock, William; Levy, George C.

doi: 10.1002/mrc.1260240910pmid: N/A

13C NMR spin‐lattice relaxation times (T1) have been measured for a series of meta‐ and para‐substituted phenylbicyclo[2.2.2]octanes in CDCl3 solution. The non‐equivalence of NT1 values (N = number of attached hydrogens) for the various protonated carbons in these molecules indicates that motion is highly anisotropic. Analysis of the T1 data using the Woessner formalism for axially symmetric ellipsoids yields a set of diffusion coefficients for overall and internal motion. In para‐substituted derivatives, motion about the symmetry axis is 3–12 times faster than motion about the perpendicular axes, depending on the substituent. Both the size (inertia) and the interacting properties of the substituent are important in determining the motional anisotropy, as indicated by the following observed order: H < NH2 < CH3 < NO2 < CH2OH < Br < NH3+ < CO2H. The change in anisotropy is a result of the anchoring effect of the substituent (via either its inertia or its hydrogen‐bonding ability), which restricts motion about axes perpendicular to the long axis of the molecule. In meta derivatives, a similar model of motional anisotropy is observed, although the absolute magnitudes of diffusion coefficients are smaller than for the para series. In both series, the bicyclooctane ring undergoes fast internal motion relative to the phenyl ring. This reflects the fact that the bicyclooctane ring is able to rotate essentially in its own volume, with minimum disturbance to neighbouring solvent molecules. On the other hand, the planar phenyl ring must displace solvent molecules as it rotates.