摘要:

Abstract13C NMR data for someN,N‐dialkylbenzylamines and their chloro‐(N,N‐dialkylbenzylamine‐6,C,N)‐tri‐phenylphosphinepalladium(II) complexes are presented and simple shift paramet

ISSN:0030-4921    

DOI:10.1002/mrc.1270220502

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractChemical shift and scalar coupling constant information has been obtained from the1H,13C,29Si and119Sn NMR spectra of a series of compounds (CH3)3SnCH2M(CH3)3, where M = Sn, Ge, Si or C and with one or two CH3(Sn) groups replaced by Cl, Br or I. The (CH3)3M and (CH3)3MCH2groups appear to have opposite substituent effects on chemical shift

ISSN:0030-4921    

DOI:10.1002/mrc.1270220503

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe13C spin–lattice relaxation times of tropine and pseudotropine have been measured in CDCl3as a function of concentration. The same relative increase in concentration serves to increase the relaxation rates much less in the region 0.9–5.0 wt.% than in the region 5.0–14.3 wt.%. The rotational diffusion coefficients have been calculated from the relaxation data using Woessner's anisotropic rotational diffusion model. Reorientation of both molecules is shown to be moderately anisotropic. The principal axes of the rotational diffusion tensor in the symmetry plane of both molecules are rotationally shifted from the principal axes of the moment of inertia tensor of the free molecules, and the main rotational axis is parallel with a line passing through the centre of mass of the molecule and the nitrogen

ISSN:0030-4921    

DOI:10.1002/mrc.1270220504

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractA number of modified retinals and retinoic esters carrying one or two methoxy groups or one methoxy and one methyl group on the polyene chain were investigated by1H and13C NMR spectroscopy. Spectral assignments were made from homo‐ and selective13C{1H} hetero‐decoupling experiments and from chemical shift comparisons. The configurations of the polyene double bonds were derived from vicinal H,H coupling constants, from1H and13C chemical shifts and by measuring nuclear Overhauser enhancements. It is found that all double bonds with no additional substituents occur in thetrans (E)and all methoxy‐substituted double bonds in thecis(alsoE) configuration. Double bonds carrying methyl groups give rise to bothcis (Z)andtrans (E)is

ISSN:0030-4921    

DOI:10.1002/mrc.1270220505

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractDipolar relaxation of15N in anilines and anilinium ions is influenced by overall motion of the molecule, by rotation about the aryl–‐nitrogen bond, by inversion of the aniline nitrogen and by interactions of the NH2or NH3+group with the solvent. These factors are assessed by comparison of the13C and15N dipolar relaxation times as a function ofpara‐substitution on the aryl ring. In the anilines (solvent CDCl3), electron withdrawal brings about faster relative motion of the amine side‐chain, contrary to expectation from consideration of CN rotation but in agreement with the effects from nitrogen inversion. The15N dipolar relaxation time correlates with the Hammett σp. For the anilinium ions (solvent Me2SO‐d6), there is no correlation with σpand no qualitative relationship with either CN rotation or N inversion. Nitrogen‐15 relaxation, corrected for overall motion as judged by ring13C relaxation, correlates with the inductive parameter σI. Electron withdrawal through induction reduces hydrogen bonding and increases side‐chain mobility. For most of the anilines and for all of the anilinium ions, solvent interactions cause the nitrogen side‐chain to be less mobile than the aryl ring. Under these circumstances, the Woessner approach cannot be used to calculate barriers. The hydrogen bond donor properties of the anilines are reduced in the absence of electron‐donating substituents, and the first barriers to NH2rotation/inversion were calculated by this procedure: aniline in CDCl33.5 kcal/mol,p‐chloroaniline in CDCl33.4 kcal/mol andp‐nitroani

ISSN:0030-4921    

DOI:10.1002/mrc.1270220506

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractCombined utilization of1H1H homonuclear and1H13C heteronuclear NMR chemical shift correlations, two‐dimensionalJ‐resolved1H NMR measurements and homonuclear1H double resonance experiments allowed specific assignments for both1H and13C NMR frequencies to be made for the tricyclic sesquiterpene cyperene. The results also provided information on the conformation of the six‐membered ring of this natural product, which was recognized as a distor

ISSN:0030-4921    

DOI:10.1002/mrc.1270220507

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

Abstract77Se and125Te chemical shifts have been measured foro‐halogenated seleno‐ and telluro‐phenetoles. Correlations exist between these parameters and the halogen electronegativities or the13C chemical shifts, except for the fluorine derivatives. The chalcogen shifts are related to the shifts of various nuclei in halobenzene derivatives, namely1H in benzenes,13C in toluenes,15N in anilines and19F in fluorobenzenes.77Se and125Te chemical shifts are correlated in theo‐halogenated seleno‐ and telluro‐phenetoles and in chalcogen analogues ofo‐methoxy‐selenoanisole and ‐tellurophenetole: Δδ(Te) = 1.60Δδ(Se). The observed gradient is close to values previously reported for other selenides and tellurides, but differs from the value observed in heterocycles. This obs

ISSN:0030-4921    

DOI:10.1002/mrc.1270220508

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

Abstract1J(13C13C) nuclear spin–spin coupling constants in derivatives of acetylene have been measured from natural abundance13C NMR spectra and in one case (triethylsilyllithiumacetylene) from the13C NMR spectrum of a13C‐enriched sample. It has been found that the magnitude ofJ(CC) depends on the electronegativity of the substituents at the triple bond. The equation1J(13C13C) = 43.38Ex+ 17.33 has been derived for one particular series of the compounds Alk3SiCCX, where X denotes Li, R3Sn, R3Si, R3C, I, Br or Cl. The1J(CC) values found in this work cover a range from 56.8 Hz (in Et3SiCLi) to 216.0 Hz (in PhCCCI). However, the1J(CC) vsExequation combined with the Egli–von Philipsborn relationship allows the calculation of the coupling constants in Li2C2(32 Hz) and in F2C2(356 Hz). These are probably the lowest and the highest values, respectively, which can be attained for1J(CC) across a triple bond. The unusually large changes of the1J(CC) values are explained in terms of substituent effects followed by a re‐hybridization of the carbons involved in the triple bond. INDO FPT calculations performed for two series of acetylene derivatives, with substituents varied along the first row of the Periodic Table, corroborate the conclusions drawn f

ISSN:0030-4921    

DOI:10.1002/mrc.1270220509

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

Abstract13C and1H chemical shifts of fourteenN‐alkylmethylquinolinium salts in DMSO‐d6are reported, and compared with those of the eleven corresponding methylquinoline bases. The influence of ring substitution by methyl groups in the salts and substitution at the nitrogen atom and the effect of the anion are discus

ISSN:0030-4921    

DOI:10.1002/mrc.1270220510

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractOn the basis of available13C NMR spectral data for indole alkaloids, substituent‐induced chemical shifts have been calculated for various types ofar‐hydroxy‐ and ‐methoxy‐substituted indole

ISSN:0030-4921    

DOI:10.1002/mrc.1270220511

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY