ISSN:0030-4921    

DOI:10.1002/mrc.1270051213

出版商:John Wiley&Sons Limited    

年代:1973

数据来源: WILEY

ISSN:0030-4921    

DOI:10.1002/mrc.1270051214

出版商:John Wiley&Sons Limited    

年代:1973

数据来源: WILEY

摘要:

AbstractCarbon and proton NMR spectra of 3‐hydroxypyridine and its O‐methyl and N‐methyl derivatives have been analysed, and are compared with the spectra of the corresponding 2‐ and 4‐substituted pyridines. It is shown, that contrary to quantum chemical predictions and in agreement with chemical experience, 3‐hydroxy‐pyridine has a phenolic structure in solution. For the N‐methyl derivative, however, carbon and proton NMR data clearly demonstrate that this compound should be formulated as N‐methyl‐3‐pyridone. The general problem of the 3‐pyridones is discussed on the basis of calculated π‐electron

ISSN:0030-4921    

DOI:10.1002/mrc.1270051202

出版商:John Wiley&Sons Limited    

年代:1973

数据来源: WILEY

摘要:

AbstractZusammenfassung‐die29Si‐NMR‐chemischen Verschiebungen δ(29Si) einer größeren Zahl von Verbindungen des Typs (CH3)4−nSiXnsowie δ(13C) einiger analoger Kohlenstoffverbindungen werden mit Hilfe von relativen paramagnetischen Abschirmungskonstanten σ* diskutiert, die nach einem vereinfachten Berechnungsverfahren bestimmt werden. Für die Berechnung von σ* werden nurp‐Orbitale berücksichtigt, als Ausgangsgrößen sind lediglilch die Elektronegativitäten von Si, C und X sowie ein einziger empirischer Korrekturfaktor erforderlich. Die berechneten Änderungen von σ* befinden sich in guter Übereinstimmung mit dem Gang der experimentellen Verschiebungen, die in den (CH3)4−nMXn‐Verbindungen in Abhängigkeit von Zahl und Art der Substituenten X beobachtet werden. Die erhaltenen Ergebnisse zeigen, daß δ(29Si) und δ(13C) im wesentlichen durch die σ‐Ladung am Si‐bzw. C‐Atom bestimmt werden und daß (p—d)π Wechselwirkungen am Si‐Ato

ISSN:0030-4921    

DOI:10.1002/mrc.1270051203

出版商:John Wiley&Sons Limited    

年代:1973

数据来源: WILEY

摘要:

AbstractThe variation in the one–bond couplings1J(CH) in vinyl derivatives with substituent has been examined. For the geminal proton1Jcorrelates very badly with substituent electronegativity but extremely well with σI, if conjugating substituents are excluded. In the case of halogen substituents the marked stereospecificity of1J(CH) for thecisandtransprotons can be rationalised in terms of an intrinsic dependence of πCHon the dihedral angle between the coupling atoms and the perturbing substituent, with an additional positive increment to theciscoupling due to direct interaction of the substituent non‐bonding electrons or to orbital circulation of the substituent electrons. The intrinsic specificity of β‐substituent effects on1J(CH) is also found in analogous compounds containing CN and

ISSN:0030-4921    

DOI:10.1002/mrc.1270051204

出版商:John Wiley&Sons Limited    

年代:1973

数据来源: WILEY

摘要:

AbstractNous mettons en évidence l'existence d'un équilibre de tautomérie dans la thiamine et ses esters phosphoriques. Et nous évaluons la position relative de l'équilibre dans ces différents composés. Le calcul permet de relier un grand nombre d'observations expérim

ISSN:0030-4921    

DOI:10.1002/mrc.1270051205

出版商:John Wiley&Sons Limited    

年代:1973

数据来源: WILEY

摘要:

AbstractProton chemical shifts, as well as solvent shifts induced by benzene, can be used for the structure determination of 4,5‐asymmetrically substituted 1‐(N‐isoimido)‐1,2,3‐triazoles, derived from the oxidation of α‐diketone bisaroylhydrazones. The geometry of the postulated ‘collision complex’ is discussed and an attempt is made to estimate theoretically the induced shifts of som

ISSN:0030-4921    

DOI:10.1002/mrc.1270051206

出版商:John Wiley&Sons Limited    

年代:1973

数据来源: WILEY

摘要:

AbstractUne étude comparée du borazine (0) et de six méthyl‐borazines (1à6) a été effectuée par RMN. Il apparaǐt nettement que le déplacement chimique des protons NCH3varie peu entre les mono‐, di‐ et triméthyl‐Nborazines alors que ce měme paramètre subit une modification importante (au total 0,21 ppm vers les champs forts) quand on passe du triméthyl‐Nborazine (HBNCH3)3à l'hexaméthylborazine (CH3BNCH3)3par substitution progressive sur les trois atomes de bore (cycles3,4, 5et6). En outre, une variation systématique du paramètre δ a pu ětre décelée entre les composés3, 4et5pour les protons qui conservent strictement le měme environnement immédiat. Une interprétation qualitative de ce résultat expérimental est proposée en termes d'effets électroniques généralisés au cycle hexagona

ISSN:0030-4921    

DOI:10.1002/mrc.1270051207

出版商:John Wiley&Sons Limited    

年代:1973

数据来源: WILEY

摘要:

AbstractThe palladium catalysed reaction of butadiene with aldehydes yields 2‐substituted 3,6‐divinyl‐tetrahydropyrans.1–4The reaction has been extended to isoprene and myrcene. With formaldehyde only 2,5‐substituted pyrans have been isolated. The isomeric tetrahydropyrans obtained were fully characterised by1H NMR, and representative 300 MHz spectra are given. Attempts to react aldehydes with 2‐methoxybutadiene were u

ISSN:0030-4921    

DOI:10.1002/mrc.1270051208

出版商:John Wiley&Sons Limited    

年代:1973

数据来源: WILEY

摘要:

AbstractThe1H NMR parameters for a number ofcis‐arylmethyl oxiranes are reported and discussed in comparison with those oftransderivatives and styrene oxides substituted in the phenyl ring. While the macroscopic behaviour of the results is in agreement with a perturbative mechanism through the oxirane ring that is mainly electrostatic in character, a small contribution due to conjugative interaction is not excluded. It seems likely that the effect of substituents in the phenyl ring is mainly transmitted through bonds rather than through space, and that the different polarisation of the CH bonds in the oxirane ring is mainly responsible for the different behaviour of the protons incis‐ andtrans‐ arylmethyl oxiranes towards the effect of subst

ISSN:0030-4921    

DOI:10.1002/mrc.1270051209

出版商:John Wiley&Sons Limited    

年代:1973

数据来源: WILEY