摘要:

AbstractThe13C NMR chemical shifts of the α, β, γ and δ carbons of aliphatic fluorides, chlorides, bromides and iodides can be reproduced by a four‐parameter equation; the chargeQon the carbon atom, the number of hydrogen atoms three bonds away,N3H, the interactions of the polarizabilities of the halogen atoms one bond away with the hydrogens present in the first sphere, as represented byPXN1H, and the polarizabilities of halogens in the second sphere,PX(2). A regression coefficient of 0.9714 and a standard deviation of 4.85 ppm are obtained for all aliphatic halides in which the R skeleton includes alkyl, acyclic and bicyclic rings. For alkyl compounds only the correlation is of the order ofR= 0.997 and the standard deviation is less than 2 ppm. Here the influence of C, H, F, Cl, Br and I are reproduced quantitat

ISSN:0749-1581    

DOI:10.1002/mrc.1260291002

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe1H (200 MHz) and13C (50.3 MHz) NMR spectra of some hexa‐ and octahydropyrazino[1′, 2′ : 1,2]pyrido‐[3,4‐b]indoles (1–13), 15‐azayohimbanes (15–18), and related compounds (14, 19, 20) are reported. The data have been analyzed in terms of the preferred conformation (9–13, 15–20) and co

ISSN:0749-1581    

DOI:10.1002/mrc.1260291003

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe1H‐ and13C NMR spectra of forskolin have been re‐investigated. Assignments are based exclusively on unambiguous carbon–carbon and carbon‐proton correlations derived from two‐dimensional NMR spectra. Stereo‐specific differentiations were deduced from selective proton NOE measurements and the interpretation of vicinal and long‐range proton‐proton scalar couplings. The proton‐proton distances calculated from proton NOE effects fit best with a flattened boat‐like conformation of ring C, which is different from the conformation of forskolin

ISSN:0749-1581    

DOI:10.1002/mrc.1260291004

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe1H and13C NMR spectra of some bis(benzocrown ethers) were recorded and assigned by means of1H/13C HETCOR spectroscopy, heteronuclear selective decoupling experiments and the refocused INEPT experiment optimized for long‐range1H,13C coupling constants. It is shown that the efficiency of the so‐called ‘biscrown effect’ is dependent on the radii of the alkali metal ions. Long‐range1H,13C coupling constants, high‐field shifts within γ‐fragments in the13C NMR spectra and NOEs from 2D‐NOESY spectra are discussed with respect to both the configuration and the preferred conformation of the s

ISSN:0749-1581    

DOI:10.1002/mrc.1260291005

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe hydroxy group of phenoxy resin has been modified by etherification and esterification. The1H NMR spectra of these products show large differences in the splitting patterns of the methylene protons according to the chemical nature of the substituent groups. Model compounds for phenoxy resin and derivatives, as well as some other glycerol derivatives, have been synthesized in order to study in more detail the signals of the CH2group. The1H NMR spectra of these compounds show two types of splitting. In some cases both protons absorb clearly as a doublet through accidental equivalence, while in other cases they are magnetically non‐equivalent. This behaviour can be explained by non uniform conformer populations (JAX≠JBX) in some cases, but whereJAX≈︁JBXit could not be explained without taking into account the molecular as

ISSN:0749-1581    

DOI:10.1002/mrc.1260291006

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe rate of interconversion between tight and loose ion pairs of lithium fluorenide in 2‐methyltetrahydrofuran was determined from7Li relaxation in the rotating frame. The rate constant for the tight to loose ion‐pair interconversion at −60°C is 2.3 × 104s−1and for the reverse process 2.6 × 103s−1. The13C relaxation times (T1) of the fluorenyl anion, adjusted for viscosity changes, do not change significantly with the ion‐pair structure. The electric quadrupole relaxation contribution to the7LiT1was derived from6Li and7LiT1measurements. Lower limits of7Li quadrupole splitting constants (QSCs) were obtained from the7Li quadrupolar and the13C dipole‐dipole relaxation times. The QSC values are in the range 37–200 kHz and appear to reflect changes in the ion‐pair structure, with a low value corresponding to a solvent‐separated ion pair. The higher value for the contact ion pair is in agreement with a structure where the anion disrupts the symmetrical coordination of solvent molecules around the cation. A decreased QSC and a shortened13CT1at high temperature for the diethyl ether solution may be

ISSN:0749-1581    

DOI:10.1002/mrc.1260291007

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractHexakis(2,3,6‐tri‐O‐nitro)‐α‐cyclodextrin and heptakis(2,3,6‐tri‐O‐nitro)‐β‐cyclodextrin were prepared and the complete assignment of the1H,13C and15N resonance signals in each case was achieved using homonuclear shift correlation experiments, one‐bond13C1H and three‐bond15NOC1H heteronuclear shift correlation measurements. The denitration of these cyclodextrin nitrates by hydroxylamine in pyridine was investigated to study its selectivity in preparing partially nitrated derivatives of these cyclodextrins. The sites of denitration were determined in each case using13C and15N NMR and the products were completely characterized. The results indicate that denitration of these cyclodextrin nitrates is a highly regiospecific reaction occurring at the 2‐position only and giving rise to hexakis(3,6‐di‐O‐nitro)‐α‐cyclodextrin and heptaki

ISSN:0749-1581    

DOI:10.1002/mrc.1260291008

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe interaction of pyrimidine with iodine when both are dissolved in a liquid crystal solvent has been studied. The considerable changes observed in the degrees of order of pyrimidine can be quantitatively attributed to complex formation between the nitrogen atoms and iodine along axes forming angles of 30° with the nitrogen–nitrogen axis and in the molecular plane. The complex formation does not affect measurably the proton and carbon positions of pyrimidi

ISSN:0749-1581    

DOI:10.1002/mrc.1260291009

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe1H CW off‐resonance decoupled13C NMR spectra of pheromones and unsaturated fatty acids were measured for the determination of the configuration of double bonds of the type CH2CH  CHCH2. The decoupling frequency corresponded to the resonance frequency of the CH2protons. The 2nd order splittings in the observed multiplets of the olefinic carbon atoms allow an approximate determination of the vicinal coupling constant between the olefinic protons, and the configurational assignment of the

ISSN:0749-1581    

DOI:10.1002/mrc.1260291010

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

Abstract1H NMR spectra of ferricytochromec‐551 were obtained in a variety of miscible aqueous buffer‐organic solvent mixtures. The pKaof a haem carboxyl group within this protein was measured in several such solvent systems. This work was facilitated by the use of the Super water eliminated Fourier transform (SuperWEFT) technique and this was extended to the suppression of multiple solvent resonances. Nuclear Overhauser enhancement difference experiments were combined with SuperWEFT, enabling structural data to be obtained in complex solvent mixtures. The data arising from this study are relevant to the evaluation and simulation of electrostatic effects in prote

ISSN:0749-1581    

DOI:10.1002/mrc.1260291011

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY