摘要:

AbstractSerinol amides of triiodoisophthalic acid bearing an acylamino group are non‐ionic x‐ray contrast agents; in addition to the expected isomerism due to hindered rotations around the amide NCO bonds, the atropoisomerism associated with the hindered rotations around the aryl–CO and aryl–N bonds was investigated by1H and13C NMR.The assignment of signal multiplicity to the different rotamers in solution for a series ofN, N′‐bis[2‐hydroxy‐1‐(hydroxymethyl)ethyl]‐2,4,6‐triiodoisophthaldiamides, 5‐substituted with (hydroxyacetyl)amino (5),S‐(–)‐ (2‐hydroxy‐1‐oxopropyl)amino (6), (hydroxyacetyl)methylamino (7), andS‐(‐)‐(2‐hydroxy‐1‐oxopropyl)‐methylamino (8) groups was approached by interpreting simpler systems such asS‐(–)‐3‐N‐[2‐hydroxy‐1‐ (hydroxymethyl)ethyl]‐5‐[(2‐hydroxy‐1‐oxopropyl)amino]‐2,4,6‐triiodoissophthalmic acid (2) and its corresponding amide 3, or more symmetric molecules such asN,N′‐bis[2‐hydroxy‐1‐(hydroxymethyl)ethyl]‐5‐amino‐2,4,6‐triiodoisopht haldiamide (4).It is shown that it is possible to discriminate between the contributions of the different types of hindered rotations in order to obtain the appropriate, although approximate, free energies of activation. Secondary aryl carboxamides 5‐8 constitute a rare case of aryl–CO hindered rotation detectable at room temperature. Analysis of the NMR data clearly indicates that in 5‐8 the population ratio of thesynandantifamilies is 1: 1 and also that of theEandZconformers. In addition, the secondary anilides 5 and 6 show fast rotation around the aryl–N bond and exhibit a conformational preference for theendoisomer only. The tertiary anili

ISSN:0749-1581    

DOI:10.1002/mrc.1260250402

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe use of weighted agreement factors in the significance testing of lanthanide‐induced shift analysis is physically meaningless, and can manipulate the resulting significance values, as confirmed by the results found with two compounds. The Hamilton ℛ factor ratio significance test and the jacknife test are compared for these compounds. The ℛ ratio test is more easily applied; the jacknife test does not show any clear advantage and is more sensitive to changes originating from the use of weighted agreement fa

ISSN:0749-1581    

DOI:10.1002/mrc.1260250403

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractSelective inverse INEPT and13C →1H →1H heteronuclear relayed coherence transfer pulse sequences were employed to assign and correlate the proton and carbon NMR spectra of methyl (5R*,6S*,8Z,11Z,14Z)‐5,6‐epoxyeicosa 8,11,14‐trienoate. The transfer of coherencefromspecific carbon nuclei in the moleculetoprotons was employed as a one‐dimensional method to correlate carbon and proton resonances. The one‐dimensional C→H coherence transfer experiments are particularly useful for C‐H correlation in situations where only a small amount of sample is available and two‐dimensional methods are only marginally applic

ISSN:0749-1581    

DOI:10.1002/mrc.1260250404

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

Abstract35Cl NQR measurements were carried out on a series of chlorobenzenes with the 1,1,3,3‐tetramethylguanidinyl substituent {TMG = –N=C[N(CH3)2]2}. The substituent constants σp, σm, σaI, and σRfor the TMG group were estimated from the relationships between the NQR resonance frequencies, νQ, and substituent constant values, σ. The νQvalue for 2‐(4‐chlorophenyl)‐1,1,3,3‐tetramethylguanidine is the lowest observed for all chlorobenzenes, and arises from the strong positive conjugative effect of the TMG group. This effect is attributed to the possible resonance stabilization of the positive charge. Steric inhibition of resonance is observed for theortho

ISSN:0749-1581    

DOI:10.1002/mrc.1260250405

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractOxygen‐17 NMR spectra of several organosulfur compounds containing the arylsulfonyl group (ArSO2–) are reported. Shielding effects are interpreted in terms of γ‐orthoCH interactions with the sulfonyl oxygens rather than conjugative interactions involving the aryl substituent and the attached SO2 group. The lanthanide shift reagent Eu(fod)3is useful for discriminating ‘internal and external’ accidental chemical shift c

ISSN:0749-1581    

DOI:10.1002/mrc.1260250406

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractAcid‐catalyzed reaction between pyridoxine and acetone produced the isomeric six‐ and seven‐membered ketals, depending on the conditions used. The structures were assigned by means of the1H and13C NMR spectra of the free bases and hydrochlo

ISSN:0749-1581    

DOI:10.1002/mrc.1260250407

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe simplest methods of 2D δ‐δ correlated spectroscopy (COSY and COSY LR) allow the easy observation of long‐range coupling interactions. It is shown how these methods can lead to the discrimination between different pathways across single bonds:4Jthrough coplanar orgauchearrangement of the bonds and5Jthrough a zig‐zag pathway or bond proximity. Applications to configurational and conformational analysis of polycyclic compounds, a trimer of isophorone, two natural terpenoids (carotol and daucol) and four steroids, are pr

ISSN:0749-1581    

DOI:10.1002/mrc.1260250408

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe multinuclear NMR spectral data for an homologous series of tertiary phosphines, R3‐nP(NMe2)n, aminophos‐phonium ions, [R3PNR′R″]+, and phosphonium ions, [R4‐nPMe]+, where R = Me, Et,n‐Pr and Ph, R′ and/or R″ = H, Me andn= 0 and 1 are reported and discussed. Quaternization by alkylation or chloramination causes an increase in the31P chemical shift (Δ δPis positive), a decrease in the13C chemical shift (Δ δCis negative) for all carbons, an increase in the magnitudes of1J(PC),3J(PC),3J(PNCH) and2J(PCH) and a decrease in the magnitude of2J(PC). Substitution of a Me2N group for an alkyl or aryl group produces an increase in the31P chemical shift and in the magnitude of1J(PC). α‐ and β‐deshielding and γ‐shielding effects are noted in the13C NMR spectra and β‐deshielding and γ‐shielding effects are noted in the31P NMR spectra with substitution on

ISSN:0749-1581    

DOI:10.1002/mrc.1260250409

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractInverse heteronuclear shift correlation via long‐range coupling to the carbonyl carbons of the cyclic hexapeptide cyclo(‐Phe11‐Thr10‐Aia9‐Trp8‐Phe/‐D‐Pro6‐) allows the sequential assignment of the amino acids. This experiment has a higher sensitivity than the convention

ISSN:0749-1581    

DOI:10.1002/mrc.1260250410

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe complete assignment of the proton and carbon spectra of globularin is presented.13C multiplicities were determined by the DEPT method; the interpretation of the spectra was achieved by comparison of heteronuclear13C‐1H chemical shift correlation,1H homonuclear correlation and1H homonuclearJ‐resolved two‐dimensional NMR sp

ISSN:0749-1581    

DOI:10.1002/mrc.1260250411

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY