摘要:

AbstractA study of the correlation of haloform proton solvent shifts in 13 aromatichydrocarbons gives clear evidence that the nature of the interactions is predominantly dipole‐induced dipole and not specific acid‐base interactions. The presence of halogen bonding interactions between the halogen atoms and the π electrons are not detected for CHCl3and CHBr3, and can only be present to a marginal extent for CHI3. The ASIS effect is not related to the molar concentration of the aromatic solvents, and the effect of alkyl substituents is explained in terms of exctuded zones around the aromatic

ISSN:0030-4921    

DOI:10.1002/mrc.1270160202

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractA study of the correlation of solvent effects on the chemical shifts of the methyl protons of sylvan, toluene and α‐picoline led to the conclusion that the preferential site of solvation of the furan ring in acidic solvents is the π‐electron cloud and not then‐electron orbital of the oxyg

ISSN:0030-4921    

DOI:10.1002/mrc.1270160203

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe mechanical and electronic design of a ‘magic angle’ NMR probe is described. This probe can be incorporated in a conventional small gap13C FT spectrometer, without any hardware or software change, to obtain high resolution13C NMR spectra on organic solids. A simple way of tuning the homogeneity and adjusting the angle is also proposed. Illustrative experimental results on various types of molecular crystals with different molecular mobilities, a clathrate compound and a polymer are discus

ISSN:0030-4921    

DOI:10.1002/mrc.1270160204

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe1H NMR spectra of the protonated and unprotonated forms ofcis‐ andtrans‐N‐methylhexahydroisoindoline, of 1,3,3,4,4‐pentamethylpyrrolidine and of 1,3,3‐trimethylpyrrolidine were analyzed. The coupling constants between the NH⊕ and the CH protons α to the nitrogen allowed the study of the conformation of the cyclic systems in ps

ISSN:0030-4921    

DOI:10.1002/mrc.1270160205

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe configurational and conformational assignments of the carbonyl group in theZ‐ andE‐1‐(3‐substituted‐5,5‐dimethyl‐2‐cyclohexen‐1‐ylidene)‐2‐butanones are carried out using only the through‐space effects of the carbonyl group. It is demonstrated that, regardless of theZ‐ orE‐configuration or the nature of the substituent in position 3, the conformation of the

ISSN:0030-4921    

DOI:10.1002/mrc.1270160206

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractCarbon‐13 chemical shifts, spin‐lattice relaxation times and nuclear Overhauser enhancement factors are reported for five polyfluoroaromatic compounds at 28°C. In all cases the relaxation of the fluorine bearing carbon is predominantly dipolar. Effective correlation times are smaller than those of the analogous benzene derivatives by a factor of 3–4, in qualitative agreement with predictions from the Stokes–Einstein diffusion theory. TheT1values for thepara‐carbon of monosubstituted fluorobenzenes is clearly shorter than theT1values for theortho‐ andmeta‐carbons. This phenomenon was traced to anisotropic tumbling, andD∥ and D⊥ diffusion coefficients were computed using Woessner's equations for molecules assumed to behave like symmetric rotors about their C2in‐plane principal symmetry axis. Equal tumbling ratios,D∥/D⊥, were found in this way for tolu

ISSN:0030-4921    

DOI:10.1002/mrc.1270160207

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe magnetic shielding constants of the1H,13C and15N nuclei of imidazole are calculated for the isolated and hydrated molecules. The results show that the hydrogen bonds produce not only large variations of the chemical shifts for the nitrogen nuclei and the NH proton which are directly involved in the intermolecular bonding, but also measurable shifts for the carbon nuclei. The calculated shielding constants and their variation with hydration are discussed in relation to experimental results concerning imidazole, the 5‐membered ring of the purine bases and the imidazole ring of histidine. The calculated values of the spin‐spin coupling constants confirm that it is possible to study the tautomeric equilibrium of the imidazole ring from the measurement of these coupling constants and that spin‐spin coupling constants are not very sensitive to solvent ef

ISSN:0030-4921    

DOI:10.1002/mrc.1270160208

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractImproved methods for the assignment of resonance multiplicity in13C NMR spectra are described. Assignments are achieved either by direct observation of resonance intensity modulations resulting from gated spin echo (GASPE) experiments, or from the derivation of ‘selected multiplet’ spectra containing only C, CH, CH2or CH3carbon resonances. The methods are time‐efficient and, by comparison with the single frequency off‐resonance decoupling assignment technique, show improved spectral resolution. Chemical mixtures are used to illustrate the procedures. Possible application to materials deriving from fossil fuel sources is con

ISSN:0030-4921    

DOI:10.1002/mrc.1270160209

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe proton magnetic resonance spectrum of partially oriented 1‐phenylpropyne has been studied and the values of the chemical shifts, the direct and the indirect coupling constants determined from the analysis of the spectrum. The ratios of the interproton distances have been derived. No significant deviations have been observed between the relative proton positions on the aromatic ring in 1‐phenylpropyne and those expected for the regular hexagonal geometry of the benzene ring. The results are insensitive to the mode of internal rotation of the methyl group about the CC

ISSN:0030-4921    

DOI:10.1002/mrc.1270160210

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractCarbon‐13 spin–lattice relaxation times and nuclear Overhauser enhancement factors are reported for triethylaluminium in toluene‐d8solution in the temperature interval 208–318 K. Aluminium‐27 linewidths are reported for the same solution in the temperature range 212–334 K. The effective correlation times at different positions in the molecule are determined and used for qualitative discussion of inter

ISSN:0030-4921    

DOI:10.1002/mrc.1270160211

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY