摘要:

AbstractThe13C NMR spectra for selected 2‐iodosobenzoic acids, their sodium salts and the sodium salts of the corresponding iodoxybenzoic acids were measured and carbon assignments made using 2D and NOE experiments and relaxation times. Iodoso and iodoxy groups deshielded theipso‐carbon in these compounds by approximately 25 and 55 ppm, respectively, relative to the corresponding iodo compounds. The13C NMR spectra of the 2‐iodosobenzoate anions were almost identical with those of the corresponding free acids, both possessing cyclic structures. The iodoxybenzoic acids are either insoluble in, or oxidize, suitable NMR solvents (i.e. DMSO‐d6, DMF‐d7). The cyclic structure postulated for iodoxybenzoate anions is supported by their13C chemic

ISSN:0749-1581    

DOI:10.1002/mrc.1260271102

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

Abstract1H and13C NMR assignments are presented for 30 oxygenated lanostane derivatives, including lanosterol, dihy‐drolanosterol, 7‐ketolanosterol, agnosterol, 24,25‐epoxylanosterol, 8α,9α‐epoxylanostan‐3β‐ol, three 15‐oxygenated derivatives of lanost‐7‐en‐3β‐ol, lanostane‐3β,7α‐diol, lanostane‐3β,9α‐diol and their acetates. These assignments, which were largely determined by a combination of DEPT, one‐boad and long‐range13C1H chemical shift correlation and lanthanide‐induced shift experiments, are not dependent on previously reported assignments, several of which were found to be incorrect.1H and13C acetylation shifts for lanostan‐3β‐ols were sufficiently invariant among the sterols studied that they were useful for assigning carbons in rings A and B. The acetylation shifts reported for l

ISSN:0749-1581    

DOI:10.1002/mrc.1260271103

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe proton and carbon spectra for the fertility‐regulating agent, pseudolaric acid B (1), have been assigned using a combination of one‐ and two‐dimensional NMR spectroscopic techniques. NOE difference measurements revealed an unexpected conformation of the molecule, which could only be explained by a strained conformation of the six‐membered lactone ring. Molecular forcefield calculations confirmed the presence of a low‐energy conformer having the lactone ring in a half‐planar conformation. The solution conformation is closely related to the solid‐state conformation. Evaluation in a broad range of human cell lines established that 1 is a general cy

ISSN:0749-1581    

DOI:10.1002/mrc.1260271104

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractSolvent‐induced13C NMR chemical shifts ofN1,N1‐dimethyl‐N2‐phenylformamidine can be correlated with the acceptor number of solvents, AN, and also with the π* and α parameters of Kamlet and Taft. No correlation was found for the height of the rotational barrier around the CN1bond. The self‐association of formamidine and the influence of polar, aprotic solvents cause an increase in ΔG1of approximately 1 kJ mol−1whereas, contrary to expectations, the ΔG1values found in hydrogen‐bonding solvents are smaller than in cyclohexane. The barrier, however, increases with the strength of the hydrogen bond and on protonation. Downfield shifts of the N1and upfield shifts of the N2signals were observed in the15N NMR spectra of formamidine when the strength of the hydrogen bond with th

ISSN:0749-1581    

DOI:10.1002/mrc.1260271105

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe dependence of thedeuterium/hydrogenNMRisotope effectson13C chemical shift (DHIECS) values on the electron density at the hydrogen (deuterium) atom in a series ofpara‐like substituted indoles with a partially deuterated NH site, measured as 0.83 M solutions in DMSO‐d6, is established on the basis of a series of correlations relating the isotope shifts with Hammett‐type í parameters,1H(NH) chemical shifts,15N chemical shifts and group electronegativity. The sensitivity of thenΔ isotope effects appears to be connected closely with electron redistribution at the 5‐substituent of the carbon atom under cons

ISSN:0749-1581    

DOI:10.1002/mrc.1260271106

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe13C resonances for all protonated carbons have been observed and assigned for the free base esters derived from the following natural products: heme d, the prosthetic group of the bacterial cytochrome oxidase cytochrome d; heme d1, the prosthetic group of the dissimilatory nitrite reductase cytochrome cd1; and a stable form of sulfheme, the chemically modified prosthetic group from the degradation product of myoglobin known as sul‐fmyoglobin. These partially saturated porphyrins have in common that a heteroatom or atoms has added to a pyrrolic carbon.13C NMR spectra were obtained on limited amounts of naturally derived samples by proton‐detected heteronuclear correlation spectrosc

ISSN:0749-1581    

DOI:10.1002/mrc.1260271107

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractA modified version of the two‐dimensional semiselective INEPT experiment is presented which allows the determination of long‐range proton‐carbon couplings in medium‐sized molecules. The difference in theT1relaxation times is utilized for the reduction of the number of protons from which coherence is transferred. This results in a simplification of the 1D and 2D spectra obtained. The capability of the proposed pulse sequence is demonstrated by the determination of the long‐range couplings in a model

ISSN:0749-1581    

DOI:10.1002/mrc.1260271108

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractHomonuclear1H COSY, long‐range COSY and relay coherence transfer (RCT) correlation spectroscopy NMR experiments were used together with fixed‐evolution HETCOR and selective INEPT spectra for complete13C and1H spectral peak assignments for tatsidine. Stereochemical and conformational assignments were made from the two‐dimensional NOE spectrum. The results of these studies confirmed the location of the methylenedioxy group at C

ISSN:0749-1581    

DOI:10.1002/mrc.1260271109

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe relative ease with which very high resolution13C NMR spectra can now be obtained because of advances in NMR technology is shown. Spectra of four alkanes were obtained at 62.9 MHz with careful shimming, low‐power decoupling and a digital resolution of less than 0.1 Hz. Signals as little as 3 ppb apart can be clearly distinguished at this moderate field strength without resolution enhancement. Consequently, additional information can be obtained. Forn‐hexadecane, six, not the usual five, signals are evident; the chemical shifts of C‐6, C‐7 and C‐8 are within 0.16 Hz (2.5 ppb) of each other and are not all the same. For 2‐methyltridecane, all 13 signals are visible; all the signals can be assigned with confidence except those for C‐7 and C‐8, which differ by only 4 ppb. For 7‐ methylhexadecane, all 17 signals are visible; many can be assigned to a specific carbon, including the signals for C‐3 and C‐14 (both of which are in CH3CH2CH2CH2CH2CH2— environments), which differ by only 37 ppb. For the two pairs of enantiomers of 2,6,10‐trimethyldodecane, all but one carbon give a pair of resonances; the two signals for C‐3 are only 2.9 ppb apart. The potential limitations on molecular size and field strength affecting line width are considered. The same solvent, concentration and temperature must be used if chemical shift data for different compounds are to be mean

ISSN:0749-1581    

DOI:10.1002/mrc.1260271110

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe1H chemical shifts and substituent chemical shifts (SCS) were recorded for several monosubstituted norbornanes and bornanes. The observed substituent effects are generally similar for the two ring systems, but difter considerably from those observed for the cyclohexanoid systems in steroids. A consistent trend for the eclipsed C‐2—C‐3 fragment in this ring system is that all the substituents produce the largest SCS on thetransoriented proton, rather than the spatially nearercisoriented proton. Indeed, for the OH substituent these SCS are opposite in sign, that for thecisoriented proton being negative (i.e. to high field). This trend is not observed in the cyclo‐hexane system, in which the distance dependence of the vicinal SCS is as expected. The major cross‐ring SCS are of the 2‐endosubstituents with the C‐6 protons, giving a large positive SCS at the 6n proton and a small negative SCS at the 6x proton. This trend is very similar to that observed in the cyclohexane ring (axial‐axial SCS), and suggests a similar electric

ISSN:0749-1581    

DOI:10.1002/mrc.1260271111

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY