Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1260240401pmid: N/A

Torri, J.

doi: 10.1002/mrc.1260240402pmid: N/A

The 13C NMR shielding effects of the carbonyl‐BF3 interaction for a series of methyl‐ and methoxy‐tetralones were determined. Once the conformations of the complexes have been defined, the major shift data which can be related to charge density changes can be qualitatively discussed in terms of the transmission of the electronic properties of the CO:BF3 group. Complexation mainly causes a reorganization of the conjugated π‐system via a resonance mechanism. Delocalization of the π‐electrons towards the BF3 electron‐withdrawing group increases the carbonyl reactivity of the base, while complex stability is favoured.

Van Haverbeke, Yves; Muller, Robert N.; Elst, Luce Vander

doi: 10.1002/mrc.1260240403pmid: N/A

As an extension of previous work on simple amino acids, deuterium nuclear relaxation rates were used to study the molecular dynamics of γ‐2,2‐[2H2]aminobutyric acid, d,l‐2‐[2H1]glutamic acid and d,l‐2‐[2H1]lysine, and also model compounds 2,2,2‐[2H3]acetic acid and 1,1‐[2H2]butylamine. This study was carried out in aqueous solution in the pH range ca 0–14. From the observed rotational correlation times and solution viscosities, molecular volumes of various ionic forms were calculated using the Gierer and Wirtz model. The results obtained are in good agreement with conformational changes expected in the pH range investigated.

Sardella, D. J.; Boger, E.

doi: 10.1002/mrc.1260240404pmid: N/A

The 13C NMR spectra of 7‐, 8‐, 9‐ and 10‐fluoro‐benzo[a]pyrenes have been recorded and the chemical shifts of all protonated (and fluorine‐substituted) carbons have been assigned. The effect of fluorine on carbon shifts (and also on electron densities, which correlate reasonably well with the shifts) is confined largely to the fluorinated ring and contiguous sites, such as peri positions or carbons across bay regions. A variety of short‐ and long‐range couplings are observed, and correlations with π‐bond orders (two‐bond couplings) and ato n polarizabilities (one‐bond couplings) are observed. Long‐range coupling patterns are less obvious, but six‐bond couplings appear to correlate with atom‐atom polarizabilities, as expected for transfer of spin information through the π‐system.

Begley, Michael J.; Crabb, Trevor A.; Roch, Olive G.

doi: 10.1002/mrc.1260240405pmid: N/A

2‐(Piperidin‐2‐ylmethyl)cycloalkanols have been synthesized by the reaction between 2‐picolyllithium and cycloalkene oxides, followed by catalytic hydrogenation of the resulting 2‐(pyridin‐2‐ylmethyl)cycloalkanols. The configurations of the 2‐(piperidin‐2‐yl‐methyl)cycloalkanols were assigned by comparing their 13C and 1H NMR parameters with those of 2‐(piperidin‐2‐ylmethyl)cyclohexanols of known (x‐ray) configuration.

Raber, Douglas J.; Hájek, Milan

doi: 10.1002/mrc.1260240406pmid: N/A

Lanthanide‐tris(fod) reagents interact reversibly in solution with Ag(fod) to form binuclear adducts having the formula AgLn(fod)4. The formation constant (K) for AgYb(fod)4 in CDCl3 is 500 M−1, and this equilibrium is in the slow exchange region below 20°C. Slow exchange is also found for AgDy(fod)4. The NMR data support a structure for the binuclear adduct consisting of an ion pair with a silver cation and a lanthanide‐tetrakis(fod) anion. The binuclear reagent associates weakly with benzene (K = 3M−1). The primary interaction involves coordination of the silver cation to the aromatic ring, and the tetrakis(fod) anion is situated in close proximity to the silver cation. Induced shifts for the aromatic moiety are primarily pseudo‐contact in origin.

Baine, Peter

doi: 10.1002/mrc.1260240407pmid: N/A

Rate constants for the interconversion of N‐trifluoroacetyl‐N‐methylbenzylamine between its conformers were measured over a temperature range by two‐dimensional NMR spectroscopy. These rate constants were compared with those obtained by line shape analysis, saturation transfer and selective pulse transfer. The rate constants measured by the two‐dimensional method were, over the temperature range of the experiments, about 40% higher than those from line shape analysis. At lower temperatures, the agreement between the two‐dimensional data and the rate constants obtained by saturation transfer and selective pulse transfer studies were much closer. The two‐dimensional NMR method for measuring rate constants gives good agreement with rate constants obtained by other NMR methods, particularly in the slow rate region.

Jenneskens, L. W.; de Kanter, F. J. J.; de Wolf, W. H.; Bickelhaupt, F.

doi: 10.1002/mrc.1260240408pmid: N/A

Carbon‐13 NMR data of [5]metacyclophane (1a), its 8,11‐dihalosubstituted derivatives 1b‐1d and of some model compounds are reported and discussed. A remarkable downfield shift is observed for the aromatic carbon between the bridging carbons; this is tentatively ascribed to long‐range effects of the bridge and to the bending of the aromatic ring.

Pandiarajan, K.; Mohan, R. T. Sabapathy; Hasan, Misbah Ul

doi: 10.1002/mrc.1260240409pmid: N/A

13C NMR spectra have been recorded for eleven piperidin‐4‐one oximes and for seven of them 1H NMR spectra have been recorded at 270 MHz. The effect of oximation on the NMR chemical shitts is discussed. The conformations of the oximes are also discussed, based on the observed chemical shifts. Although several oximes appear to adopt a chair conformation, in the same manner as the corresponding ketones, the oximes of 3,5‐dimethyl‐2,6‐diarylpiperidin‐4‐ones with cis‐methyl groups seem to adopt an asymmetric non‐chair conformation. Analysis of the chemical shifts of cis‐2,6‐dimethylcyclohexanone oxime suggests that this compound also exists in a non‐chair conformation, and not in a chair conformation with two axial methyl groups as suggested previously.

Sydnes, Leiv K.; Skjetne, Tore

doi: 10.1002/mrc.1260240410pmid: N/A

COSY and NOESY spectra (400 MHz) have been used to complete the assignment of the 1H NMR spectra of 1‐ and 3‐nitrobenzo[e]pyrene. Both compounds show strong bay region nuclear Overhauser enhancement and significant coupling across bay regions. Both compounds also exhibit extensive long‐range couplings. For 1‐nitrobenzo[e]pyrene the most spectacular couplings are between H‐4 and H‐6 and between H‐4 and H‐8. The most unusual long‐range couplings in 3‐nitrobenzo[e]pyrene are between H‐1 and H‐5, H‐2 and H‐7 and H‐4 and H‐8. Simulation of the spectra reveals that all short‐range coupling constants are normal, and confirms the presence of the long‐range couplings.