ISSN:0030-4921    

DOI:10.1002/mrc.1270081115

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractSubstituent shift effects on geminal protons are consistent with cumulative α‐, β‐ and γ‐effects of a long chain substituent, e.g. whereby not only the first, but also the subsequent β‐ and γ‐atoms of the sidechain should be taken into consideration. These shift contributions depend on rotational conformation in a way that lends itself to calculation where the necessary data are available. Therefore the shifts of the unsubstituted parent compound, the individual increment‐contributions of the β and γ groupings and the rotameric distribution must be known. This would enable, conversely, a semi‐quantitative prediction of one of these parameters if the o

ISSN:0030-4921    

DOI:10.1002/mrc.1270081102

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractIt is shown that the proton chemical shift may be predicted with fairly good precision for a proton in an ethano fragment carrying a (long) vicinal substituent. Caution must be used however in calculating geminal effects.

ISSN:0030-4921    

DOI:10.1002/mrc.1270081103

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractNous avons enregistré les spectres RMN du13C d'une série de quatorze chlorocyclohexanones afin d'examiner les variations du déplacement chimique du13C en fonction de la position de l'orientation et du nombre de substituants chlore. On détermine par comparaison entre les valeurs des déplacements chimiques expérimentaux et calculés de molécules chlorée, des incréments Δδ13C et les conditions de leur additivité. La comparaison des déplacements chimiques observés et calculés dans le cas de molécules mono et dichlorées en interconversion, montre que les effets du chl

ISSN:0030-4921    

DOI:10.1002/mrc.1270081104

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractThe vitamins, pyridoxine, pyridoxal, pyridoxamine, pyridoxal‐5′‐phosphate and pyridoxamine‐5′‐phosphate, have been studied in aqueous solution over a pH range of 2–12 by13C nuclear magnetic resonance spectroscopy. Resonance assignments are made primarily by the spin–spin coupling constants of carbons with protons and with phosphorus. The proton–carbon coupling constants show a marked conformational dependence in the hemiacetal form of pyridoxal. Furthermore, the H‐6C‐5 coupling constant in the vitamins is much smaller than the corresponding constant in pyridine. This may be due either to an effect of the C‐5 substituent in vitamins or to a different electronic configuration of the zwitterionic hydroxypyridine ring. The addition of manganese to a solution of pyridoxal phosphate causes line broadenings consistent with the interaction of the metal ion with this vitamin at the formyl and phenolic oxygens. The chemical shifts of the aromatic carbons of pyridoxine have been calculated, as a function of pH, by summing shielding parameters which were estimated empirically from pyridine derivatives. The calculated shifts agree well with the experimental data for C‐3, C‐5 and C‐6, less well for C‐2, and poorly for C‐4. The deviation from additivity for C‐4 indicates a preferred orientation for the 4‐hydroxymethyl substituent caused by internal hydrogen bonding between the substituents at C‐3 and C‐4. Evidence is presented for the existence of the free aldehyde form of pyridoxal at alkaline pH. Aldimine complexes of pyridoxal and pyridoxal phosphate with amines and amino acids have also been studied. Characteristic chemical shift changes caused by both pyridinium and aldimine nitrogen deprotonations are seen. Additionally, the chemical shifts of carbons of the pyridine ring are dependent upon the structure of the imine, especially when the aldimine nitrogen is protonated. We conclude that this dependency is due to steric effects in an aldimine complex which is constrained by internal hydrogen bonding. We also discuss the merits of carbons 3 and 4 as possible sites

ISSN:0030-4921    

DOI:10.1002/mrc.1270081105

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractL'analyse des spectres de résonance magnétique nucléaire des deux isomères du triméthyl‐1,6,6 phényl‐3 dioxa‐2,8 aza‐5 phosphav‐1 bicyclo [3.3.0]octane permet de proposer une conformation pour chacun des cycles pentagonaux d'une part, et une configuration de l'atome de phosphore d'autre part. La mobilité du proton HP, révélée par des expériences à haute température et par l'échange PH ⇌ PD, est sensiblement di

ISSN:0030-4921    

DOI:10.1002/mrc.1270081106

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractAt the present time no completely satisfactory quantum mechanical calculations exist for carbon, proton or fluorine chemical shifts in various substituted aromatic or olefinic systems. However, the chemical shifts in such systems have been shown to be well correlated by a linear multiple regression analysis with the Swain and Lupton field and resonance para meters ℱ and ℛ, and the semiempirical parameterQ. The utility ofQin testing substituent stereochemistry has been exemplified previously. Here the applications of the complete regression analysis to a wide variety of different systems for the three nuclei are given. The correlation is also shown to apply to selenium in substituted selenophenes. The13C chemical shifts for a series oforthosubstituted toluenes are presented and comparisons made with otherorthodisubstituted benze

ISSN:0030-4921    

DOI:10.1002/mrc.1270081107

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractThe13C n.m.r. spectrum of mutarotatedD‐ribose is completely assigned by using 2‐ and 3‐deuterio‐D‐ribose as reference compounds. The signal intensities of the largely relaxed13C n.m.r. spectrum are evaluated, and the equilibrium mixture of mutarotatedD‐ribose is found to consist of 6·1% α‐furanose, 11·6% β‐furanose, 20·3% α‐pyra

ISSN:0030-4921    

DOI:10.1002/mrc.1270081108

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractEs wird ein Verfahren beschrieben, das eine Reaktion direkt im Spektrometer zu beobachten erlaubt, bei der kontinuierlich ein gasförmiger Reaktand über eine Glaskapillare in das rotierende 5 mm‐Proberöhrchen eingeleitet wird. Bei richtiger Versuchsführung werden die Signale durch die Kapillare und die aufsteigenden Gasblasen nur unwesentlich verbreitert (Halbwertsbreiten<1 Hz). Eine Versuchsanordnung mit zwei Kapillaren gestattet, gleichzeitig zwei gasförmige Reaktanden zuzuführen and deren Reaktion zu verfolgen. Als Beispiel für die Anwendungsmöglichkeiten dieser Methode werden die bei der Autoxidation von Trialkylboranen aufgenommenen Protonenresonanzspektre

ISSN:0030-4921    

DOI:10.1002/mrc.1270081109

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractThe barrier to internal rotation in a series ofp‐substituted acetophenones has been determined by means of low temperature carbon‐13 n.m.r. and total bandshape analysis, resulting in: ΔG 140≠= 5·4 ± 0·1 kcal mol−1(22·4 ± 0·4 kJ mol−1) for the unsubstituted acetophenone. The substituent effects on the barrier are found to be the same as for the corresponding benzaldehydes. The barrier height is discussed in terms of contributions from resonance

ISSN:0030-4921    

DOI:10.1002/mrc.1270081110

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY