摘要:

AbstractThe n.m.r. spectra of various derivatives of the cyclic acylal of malonic acid and of dimethylbarbituric acid are described. From the long range coupling constant, conformational evidence on the dihedral angle θ between the aromatic ring and the diketodioxane ring or theN,N‐dimethylbarbituric acid ring can be derived. The investigated substances show a dependence of θ on the aromatic substitut

ISSN:0030-4921    

DOI:10.1002/mrc.1270090102

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractThe natural abundance13C magnetic resonance spectra of reduced proaporphines are reported, with complete assignments based on peak multiplicity and empirical calculations of chemical shifts. The chemical shift values of C‐8, C‐12 and C‐7 are found to be strongly diagnostic of the spiro carbon configur

ISSN:0030-4921    

DOI:10.1002/mrc.1270090103

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

Abstract13C n.m.r. spectra of a number of methyl substituted cyclohexanes, some of them conformationally homogeneous, have been recorded in CDCl3and used to determine shift effects engendered by the introduction of methyl groups on carbon atoms remote from the site of substitution. Sizeable changes in shifts are found, including a substantial effect of an equatorial methyl group on an axial methyl group δ to it (+0.67ppm, ‘δea’). The effects reported are of consequence in investigations of conformational problems by13C n.m.r. techn

ISSN:0030-4921    

DOI:10.1002/mrc.1270090104

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractThe13C chemical shifts of several alkyl and phenyl substituted pyrylium perchlorates, together with related pyridine and pyridinium salts, are reported. The shifts in the isoelectronic series benzene, pyridine, pyrylium cation correlate well with charge densities calculated by INDO MO theory. Charge densities also account for the shift changes found at C‐3, C‐4 and C‐5 for protonation of pyridine and 2,4,6‐trimethylpyridine. The shift changes observed on protonation for C‐2 and C‐6, along the series pyridine, 2,4,6‐trimethylpyridine and 2,4,6‐triphenylpyridine can only be rationalized by consideration of both charge density and π‐bond order changes. The effects of alkyl substitution on the shifts of the pyrylium cations are not accounted for by charge density changes. Empirical correlations of these shifts with literature data for the alkylbenzenes and the shifts of the phenyl substituted 6‐membered hetero

ISSN:0030-4921    

DOI:10.1002/mrc.1270090105

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractThe polymerization of 1,1,1‐trifluoroacetone with aliphatic secondary amines is reported. The polymerization product is found to be a mixture of four diastereoisomers of the cyclic trimer, the structure of which has been determined using proton and fluorine magnetic resonance spectroscopy. The proportions of the isomers have been estimated to be 70:19:8:3 from the19F resonance spectrum. A comparative study of the reaction products of trifluoroacetone with metallic sodium and diethylamine is also discusse

ISSN:0030-4921    

DOI:10.1002/mrc.1270090106

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractThe n.m.r. spectra of triterpenoids related to 12‐ursene have been examined using the shift reagent Eu(fod)3. The assignment of all the methyl resonances has been achieved for ursolic acid derivatives and the corresponding compounds of the 3‐epi series, which have not been investigated previously. The additive shielding effects of various substituents on the methyl resonance frequencies have been deduced from the resu

ISSN:0030-4921    

DOI:10.1002/mrc.1270090107

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

Abstract13C chemical shifts and31P13C spin–spin coupling constants are reported for 10 alkyl‐, 20 benzyl‐ and 3 (naphthylmethyl)‐phosphonates. While in saturated aliphatic chains P–C couplings over more than four bonds cannot be resolved, couplings over up to seven bonds are observed in the benzyl type systems. Conformational and substituent effects onJ(PC) are studied and discussed.nJ(PF) (n = 4, 5, 6) are reported for the isomeric (fluorobenzyl)phosphonates andnJ(PP) (n = 5, 6, 7) were obtained from the13C satellites in the31P n.m.r. spectra of the isomeric diphosphonates, C6H4[CH2P(O)(OEt)2]2. Comparison of those13C absorptions of the latter, which represent the X parts of ABX or AA′X spin systems, with the spectra of the corresponding (methylbenzyl)phosphonates, CH3C6H4CH2P(O)(OEt)2, yielded the relative signs ofnJ(

ISSN:0030-4921    

DOI:10.1002/mrc.1270090108

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractTotal bandshape analysis of the temperature‐dependent n.m.r. spectrum of the bridge methylene protons in 6,6‐dicarbethoxy‐1,2,3,4‐dibenzcyclohepta‐1,3‐diene has been carried out to yield the following activation parameters: ΔG 298K‡= 60.96 ± 0.17 kJmol−1(14.57 ± 0.04 kcal mol−1), ΔH‡= 47.3 ± 0.8 kJ mol−1(11.3 ± 0.2 kcal mol−1) and ΔS‡= −45.6 ± 3.3 J mol−1K−1(−10.9 ± 0.8 cal mol−1K−1). A value of ΔG‡in agreement with the above may be obtained from a bandshape analysis (at a suitable temperature) of the spectrum of the methylene protons in the carbethoxy groups. In our opinion, the rate process described by these activation parameters must be the configurational inversion of the biphenyl system, and thus the polarimetric data on this compound reported by Iffland and Siegel [J. Am. Chem. Soc.80, 1947 (1958); half‐life of 80 min at room temperature] are seriously called to question, as previously noted by Sutherland and Ramsay [Tetrahedron21, 3401 (1965)]. We have attempted unsuccessfully to repeat the polarimetric work, and have been able to show by means of thin‐layer chromatography in the cold, mass spectral analysis and polarimetry that an optically active impurity (as yet unid

ISSN:0030-4921    

DOI:10.1002/mrc.1270090109

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractThe carbon‐13 n.m.r. spectra of some 3‐substituted‐2‐cyclohexenones show very wide variations in chemical shift at C‐3 that correlate with Pauling electronegativity χ, even wider variations at C‐2 that correlate with the Taft resonance parameter σRº and almost no variation at C‐1. These very different effects are shown to be consistent with the electronic distribution for these and related compounds revealed by other spectroscopic techniques. Reasons for the insensitivity of carbon‐13 n.m.r. to configurational and conformational variation in simple enamino‐k

ISSN:0030-4921    

DOI:10.1002/mrc.1270090110

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractThe1H and13C n.m.r. spectra ofN‐methylated pyridine, pyridazine, pyrimidine and pyrazine andN,N‐dimethylated pyrimidine and pyrazine have been recorded and analysed. The change in the13C chemical shifts under the influence ofN‐methylation (Δδ) in the diazabenzenes could be predicted by the Δδ values of pyridine. A comparison of the Δδ values ofN‐methylation with those ofN‐protonation showed that both reactions have a

ISSN:0030-4921    

DOI:10.1002/mrc.1270090111

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY