摘要:

Abstract13C,15N and17O NMR chemical shifts, and also1J(CH) and1J(NH) values, have been determined for variously substituted sulphonamides and some sulphinamides, either neat or in acetone or dimethyl sulphoxide solution.The effect of benzene ring substituents on the chemical shifts of nitrogen and oxygen nuclei is slight, butN‐substitution changes the shielding of both nuclei. Generally, anN‐methyl substituent shields an amide nitrogen and anN,N‐dimethyl substituent gives further slight shielding. On the other hand, anN‐phenyl substituent deshields the nitrogen strongly, but the deshielding effect of anN,N‐diphenyl substituent is markedly smaller. The sulphonyl oxygens are deshielded relative to the sulphinyl oxygens, andN‐methyl andN,N‐dimethyl substituents shield the oxygen nucleus. The effect ofN‐phenyl andN,N‐diphenyl substituents on the shielding of the oxygen atoms of the sulphonyl group is slight.The direct1J(CH) coupling constants are similar, but they are characteristic of different type of sulphur amides. The1J(NH) values are of the same order of magnitude for sulphonamides and sulphinamides, but are clearly smaller forN‐unsubstituted amides than forN‐

ISSN:0749-1581    

DOI:10.1002/mrc.1260250302

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThree groups of alkyl‐substituted naphthazarins were studied by1H and13C NMR in chloroform‐dat ambient temperature. Preliminary1H NMR studies were carried out on selected members of each group at low temperatures (down to –120 °C) in dichloromethane‐d2solution. Monoalkylnaphthazarins were found to exist predominantly as the 2‐alkyl tautomers (I) and the dimethylalkyl species as the 2,3‐dimethyl‐6‐alkyl tautomers (I). However, both symmetrically and unsymmetrically substituted 2,6‐ and 2,7‐dialkylnaphthazarins exhibited averaged chemical shifts and coupling constants indicating rapid proton exchange between the two minimum energy 1,4‐dione tautomers (IandII).13C NMR shifts were utilized to calculate tautomer populations of the unsymmetrical 2,6‐ and 2,7‐(

ISSN:0749-1581    

DOI:10.1002/mrc.1260250303

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe13C NMR resonances of a series of pseudoguaianolides are reported, which have been assigned on the basis of multiplicities, chemical shift theory and comparison with related substances.

ISSN:0749-1581    

DOI:10.1002/mrc.1260250304

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractTheE/Zconfigurational equilibrium of the nitroethylenic moiety of the antiulcer agent ranitidine was studied in aqueous solution and in DMSO‐d6and CDCl3using1H and13C NMR spectroscopy. In aqueous solution the room temperatureE/Zisomerization of the unprotonated nitroketenediamine moiety is fast on the NMR time scale, but becomes slow for the species protonated at this moiety owing to intramolecular hydrogen bonding between the nitro group and a neighbouring NH2R+group. In DMSO‐d6a free energy of activation of the order of 70 kJ mol−1was estimated for theE/Zisomerization of the unprotonated moiety of ranitidine, in good agreement with values previously found for 2,2‐disubstituted nitroethylene model co

ISSN:0749-1581    

DOI:10.1002/mrc.1260250305

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe interaction of β‐cyclodextrin with propanolol hydrochloride was shown by NMR to produce diastereomeric pairs observable in D2O solution at 400 MHz. By addition of racemate to pure (–)‐isomer, the usefulness of this novel technique in being able to measure optical purity in water down to the 1% level was demonstrated. Using changes in chemical shifts and NOE effects, a possible structure for the inclusion complex is proposed. γ‐Cyclodextrin induced larger shifts in the spectrum than the β‐equivalent, whereas α‐cyclodextri

ISSN:0749-1581    

DOI:10.1002/mrc.1260250306

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe absolute configuration of an unknown 2′‐ or 4‐ and (or) 4′ phenyl‐substituted chalcone oxide can be predicted from the chemical shift behaviour of the1H NMR spectrum of the substrate in the presence of the lanthanide chiral complex

ISSN:0749-1581    

DOI:10.1002/mrc.1260250307

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractHydrophobic binding of 2,2‐dimethyl‐2‐silapentane‐5‐sulfonate (DSS) to guanosine 5′‐monophosphate (5′‐GMP) and cytidine 5′‐monophosphate (5′‐CMP) results in an upfield shift of the1H NMR trimethylsilyl resonances with respect to an internal reference tetramethy lammonium ion. The nature of the nucleotide‐DSS interaction and the stability of the resulting complexes have been studied. The magntiude of the effect is dependent on the nature and extent of the self‐association of the nucleotide and the nucleotide concentration. For nucleotides which self‐associate non‐cooperatively to form disordered base stacks, such as Li2(5′‐GMP) and M2(5′‐CMP), where M = Li+, Na+, K+and Rb+, the formation of 2 : 1 complexes (nucleotide to DSS molar ratio) has been proposed. Apparent equilibrium constants for the 2 : 1 complexes are 0.44 M−2for Li2(5′‐GMP) at 2 °C and an average value of 0.30 M‐2for M2(5′‐CMP) at 1 °C. For the Na+and Rb+salts of 5′‐GMP, which form strongly associated, ordered self‐aggregates, the interaction between DSS and 5′‐GMP is considerably reduced owing to the inabilit

ISSN:0749-1581    

DOI:10.1002/mrc.1260250308

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of five pairs of 18β‐ and 18°‐11‐oxooleanolic acid derivatives have been assigned. The chemical shifts of C‐12, C‐13, C‐17, C‐18 and C‐28 are of diagnostic value for the determination of the D/E junctio

ISSN:0749-1581    

DOI:10.1002/mrc.1260250309

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe1H and13C NMR spectra of amiodarone and several derivatives are reported and assigned. The hypothesis of anO‐transtoO‐cisconformational equilibrium in most of these molecules has been investigated by examining the1H and13C chemical shifts, and by NOE and LIS experiments, variable‐temperature NMR and IR spectroscopy.The assumedO‐trans/O‐cisequilibrium would be fast on the NMR time scale for amiodarone, which has noorthosubstituents on the C‐3 benzoyl substituent. However, in the 2′,6′‐dibromobenzoyl derivatives, separateO‐transandO‐cisconformers are observed at room temperature in the NMR spectrum in the ratio ofca60:40, favouring theO‐transconformer. The coalescence temperatures and activation energies (ΔG Tc≠) of the 2′,6′‐disubstituted compounds are obtained; the activation energy increases with the size of theorthosubstituents but the conformer ratio remains unchanged. In contrast, removal of the C‐2 butyl substituent on the benzofuran ring

ISSN:0749-1581    

DOI:10.1002/mrc.1260250310

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe structure of nitroguanidine was investigated by the application of15N,1H and13C NMR spectroscopy of a fully15N‐labeled sample in DMSO‐d6and DMF solutions and by15N CP/MAS NMR in the solid state. These spectra confirm the nitroimine structure which has been suggested by other investigations in recent years, and do not lend any support to the commonly used nitroamine structure or for a tautomeric equilibrium with the nitroamine. Useful15N spin coupling constants to the1H and13C nuclei in the assigned structure are repor

ISSN:0749-1581    

DOI:10.1002/mrc.1260250311

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY