摘要:

Abstract13C NMR spectra of compounds related to aristolochic acid and aristololactam, the constituents ofAristolochia indica, have been studied to determine the chemical shifts and coupling constants of polysubstituted phenanthrenes. Selective1H decoupling and long‐range couplings were utilized for the assignments. Substituent‐induced chemical shifts and also the effects on coupling constants could be deduced in some cases. Anion formation was found to be particularly helpful in the interpretation of the spectra of carboxylic compounds. Shift assignments of some structurally related compounds could also be m

ISSN:0030-4921    

DOI:10.1002/mrc.1270221202

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe17O NMR spectra of 3‐alkoxythiolane 1,1‐dioxides indicate that the sulfonyl oxygens are diastereotopic but their chemical shift differences are essentially independent of the structure of the alkyl group in the alkoxy moiety. Eu(fod)3enhances the17O chemical shift differences between the diastereotopic sulfonyl oxygens in 3‐isopropoxythiolane 1,1‐dioxide and shifts both oxygens upfield. α,β‐Unsaturation deshields the sulfonyl oxygens in both five‐ and six

ISSN:0030-4921    

DOI:10.1002/mrc.1270221203

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe17O NMR spectra for a series of17O‐enrichedp‐substituted benzoic acids, methyl benzoates, cinnamic acids and methyl cinnamates in acetone at 40°C are reported. The carboxylic acids showed one signal (benzoic 250.5 ppm, SCS rangep‐MeO top‐NO2= 10.5 ppm; cinnamic 254.1 ppm, SCS rangep‐MeO top‐NO2= 5.4 ppm). The esters showed two signals [methyl benzoate (CO) 341.3 ppm and (OCH3) 128.0 ppm; methyl cinnamate (CO) 339.9 ppm and (OCH3) 134.2 ppm]. The SCS ranges for the carbonyls of the esters were larger than those for the corresponding acids, while those for the OCH3groups of the esters were slightly smaller. The carbonyl data gave good correlations with σ+constants, while the OCH3data gave at best only a poor correlation with σ constants. Dual substituent parameter treatment improved the correlations for all the data using σR+constants. The ratios of ρIto ρR+were similar for

ISSN:0030-4921    

DOI:10.1002/mrc.1270221204

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe17O chemical shifts for six cyclic ketones which serve as models for quinones, viz. cyclohex‐2‐enone (1), α‐tetralone (2), anthrone (3), 4H‐pyran‐4‐one (4), 1‐benzopyran‐4(4H)‐one (5), xanth‐9‐enone (6), and for six quinones, viz. benzoquinone, naphthoquinone, anthraquinone, 2,5‐dihydroxybenzoquinone 5,8‐dihydroxynaphthoquinone and 1,4‐dihydroxyanthraquinone, were measured in toluene at 90°C. A shielding effect of approximately 50 ppm per fused benzene ring was noted for the quinones and related carbocyclic ketones; however, the analogous series of heterocyclic fused ring ketones 4–6 showed only a slight fused‐ring effect on the carbonyl chemical shift. A single17O resonance was observed for 2,5‐dihydroxybenzoquinone (358 ppm) and 5,8‐dihydroxynaphthoquinone (283 ppm), indicating rapid proton exchange between the oxygen atoms of these compounds. However, 1,4‐dihydroxyanthraquinone gave two discrete17O signals at 441 and 87 ppm, indicating that in this case proto

ISSN:0030-4921    

DOI:10.1002/mrc.1270221205

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe ENDOR spectrum of the triphenylmethyl radical formed by heat treatment of triphenylmethane has been measured in solution at 131°C. The derived hyperfine coupling constants of 2.770, 2.556 and 1.138 G were used to simulate the extremely well resolved EPR spectrum. These coupling constants are in good agreement with spin densities determined for the planar radical by the McLachlan method

ISSN:0030-4921    

DOI:10.1002/mrc.1270221206

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractVicinal thallium–hydrogen coupling constants are used to discuss conformations in dicyclohexylthallium chloride, bis(4‐methylcyclohexyl)thallium chloride and bis(4‐tert‐butylcyclohexyl)thallium chloride. Thallium does not have a very strong preference for equatorial positions in dicyclohexylthallium chloride, whereas bis(4‐alkylcyclohexyl)thallium chlorides exist largely in one conformation. Bis(4‐methylcyclohexyl)thallium chloride exists in three isomeric forms; the major product appears to be thecis‐isomer (equatorial methyl, axial thallium), with the other two isomers probably containing thalliumtransto the methyl group (axial thallium being preferred). The preference for thecis‐isomer (equatorialtert‐butyl, axial thallium) of bis(4‐tert‐butylcyclohexyl)thallium chloride is such that other iso

ISSN:0030-4921    

DOI:10.1002/mrc.1270221207

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe proton NMR spectra of the free base porphyrins γ‐meso‐dimethylaminopyrroetioporphyrin‐XV (1) and the corresponding γ‐diethylamino compound 2 show no temperature dependence, and are interpreted as being due to an essentially orthogonal conformation of the γ‐NR2substituents. However, both of the corresponding dications 3 and 4, respectively, in CDCl3–TFA solution, give temperature‐dependent proton NMR spectra. Nuclear Overhauser enhancement difference spectra allow complete assignment of the spectrum of 3, and hence the interpretation of the temperature dependence. The spectra arise from a skew conformation of the NR2groups in which the barrier to rotation through the orthogonal conformation isca13.6 kcal mol (56.8 kJ mol−1), and the barrier to rotation through the planar conformation

ISSN:0030-4921    

DOI:10.1002/mrc.1270221208

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

Abstract1H and13C NMR spectral data for 21N‐methyltetrahydroquinoxalines annelated with furan, pyrrole, imidazole or thiazole rings are reported. Unambiguous assignments of the ring junction13C resonances were made on the basis of selective decoupling experiments and with the aid of one‐bond and long‐range13C–1H coupling constants. The effects of five‐membered heterocycles on the1H and13C chemical shifts of the ring junction hydrogen and carbon atoms are considered. Values of one‐bond1J(CH) and vicinal3J(HH) coupling constants between the ring junction protons are also discussed as a diagnostic means for structural elucidation of tetrahydroquinoxalines condensed with five‐membered

ISSN:0030-4921    

DOI:10.1002/mrc.1270221209

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe 500 MHz proton NMR spectra of chlorophyll‐ain several non‐aggregating solvents, at high dilution, are given and that of pheophytin‐ain CDCl3at 360 MHz and at high dilution is reported. Under these conditions, the dispersion is such that separate resonances are observed and can be assigned for all protons in the molecules, except P‐5 to P‐15 in phytyl side‐chain. The complex spin systems of the C‐7 propionic ester side‐chains, and of the P‐1/P‐2 fragment, are analysed and the couplings obtained are interpreted in terms of possible conformation

ISSN:0030-4921    

DOI:10.1002/mrc.1270221210

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractHigh‐resolution13C NMR spectra of solid 1,4‐bis(n‐butylamino)anthraquinone are presented. In spectra measured at 22.6 MHz the effects of two short‐range and two long‐range residual (13C,14N) dipolar couplings have been observed. Only the short‐range effects are observable in the 50.3 MHz spectra. These typical asymmetric doublets allow the determination of the14N nuclear quadrupole coupling constant (χ=e2Qq/h=−3.0 MHz), the asymmetry parameter (η=0.3) and the orientation of the electric field gradient tensor of the14N in the mole

ISSN:0030-4921    

DOI:10.1002/mrc.1270221211

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY