摘要:

AbstractThe eight spin NMR spectrum (400 MHz) of bicyclopropylidene oriented in a nematic phase has been analysed. The absolute signs and values of5J(HH) long‐range spin‐spin coupling constants have been determined for the first time for this molecule. The ratios of interatomic HH distances have been deduced from the direct coupling cons

ISSN:0030-4921    

DOI:10.1002/mrc.1270190202

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe1H NMR Spectra of 28 substituted phenazines have been measured and analysed with computer assistance. Substituent increments of chemical shifts were calculated for methoxy, carbomethoxy and methyl derivatives. The influence of these substituents on coupling constants has been examined.

ISSN:0030-4921    

DOI:10.1002/mrc.1270190203

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe structure of the carbanionic species 4 formed from diethyl(2‐oxopropyl)phosphonate andt‐BuOK has been studied by1H,13C and31P NMR. In an associating medium (pyridine), a single chelated (C) carbanionic species 4Z(C) is observed. Two slowly interconverting species 4Zand 4Eco‐exist when the anion‐cation interaction is loose, i.e. in Me2SO and when the gegenion K+is complexed to (2,2,2)cryptand in Me2SO. The anionic carbon of 4Zand 4Eis planar, and they have a strong enolate character as shown by the barrier to rotation around the C‐1C‐2 bond (ΔGc‡∼92 KJ mol−1). Their structures are compared to those of the relatedEandZ1‐diethylphosphonato‐2‐trimethylsilyloxypropenes and to (acetylmeth

ISSN:0030-4921    

DOI:10.1002/mrc.1270190204

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe13C and77Se NMR spectra of eight new unsubstituted biheterocycles containing a thiophene or selenophene ring condensed with an isothiazole or isoselenazole ring were recorded. The assignments of the13C signals were made by the examination of chemical shifts,1J(CH) coupling constants and, for the quaternary carbons, on the basis of1J(C,77Se) coupling constants. The results are compared and discussed.

ISSN:0030-4921    

DOI:10.1002/mrc.1270190205

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe population ratios of thesynto theanticonformers in 9‐(2‐substituted phenyl)fluorenes have been determined by1H NMR spectroscopy to range from 0.25 (for 2′;‐NH2) to>20 (2′;‐CHNNHC6H3(NO2)‐2,4). They appear to increase, firstly, with the steric bulk of the 2′;‐substituents and, secondly, with the electronic repulsion between the substituent and the π electrons on the fluorene ring. The unusually low population of thesynisomer in the 2′;‐NH2compound was found by IR absorption to be due to stabilization of theantiform by NH …︁ π hydrogen bonding. Whereas the substituents on the fluorene ring do not affect the population of the two isomers in 9‐(2‐tolyl)fluorenes, the same series of substituents exhibit a positive slope in the Hammett plots of the equilibrium constants in 9‐(2‐methoxymethylphenyl)fluorenes. Through‐space interaction between the methoxymethyl group and the π‐donating fluorene ring is postulated. The free energy of activation (ΔG‡) for the interconversion between the two conformers in 9‐(2‐substitued phenyl)fluorenes have been obtained from the line‐shape depindence on temperatures. The ΔG‡ values ranged from 56.8 (for 2′‐NH2) ot 78.6kJ mol−1when there is no fluorene ring substituent. IN three typical examples, a full line‐shape analysis gave, additionally, the ΔH‡ and ΔS‡ data of the interconversion. Introduction of a meth

ISSN:0030-4921    

DOI:10.1002/mrc.1270190206

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractA survey of18O isotope effects on13C chemical shifts shows that a linear relationship exists between the magnitude of the one‐bond isotope effect and the chemical shift of the carbon atom for carbonyl groups. No such correlation was found for functional groups in which the oxygen atoms are connected to the carbon atoms via single bond

ISSN:0030-4921    

DOI:10.1002/mrc.1270190207

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe13C NMR chemical shifts of α‐pinene andcis‐ andtrans‐pinanes have been reassigned on the basis of deuterium exchange experiments. Hydrogen at allylic positions in α‐pinene is exchanged for deuterium by treatment with D2over an amorphous Pd‐Si alloy. Further reaction gives a mixture of pinanes labelled at four positions. The newly assigned shifts correspond well with other examples of confomationally dependent shifts in bicyclo[3.1.1]heptane

ISSN:0030-4921    

DOI:10.1002/mrc.1270190208

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

Abstract13C NMR spectra (22.63 MHz) of 23 cyclic amine derivatives ofN‐alkynylphthalimides,N,N′;‐dialkynylpyromellitic acid diimides,N‐alkynyloxyphthalimides and 5‐p‐chlorophenyl‐2‐(4‐t‐amino‐2‐butynyl)thio‐1,3,4‐thiadiazoles were analysed. The influence on the13C chemical shift of oxygen insertion between the nitrogen of the phthalimides and the met

ISSN:0030-4921    

DOI:10.1002/mrc.1270190209

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of a number of partial clerodane structures and analogous compounds were recorded. The information thus obtained enabled the assignment of the13C NMR shifts in a number of naturally occurring clerodanes.

ISSN:0030-4921    

DOI:10.1002/mrc.1270190210

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

Abstract13C NMR chemical shifts and13C31P couplings are reported for triphenyl phosphate and 13 alkyl derivatives. Inortho‐alkylated materials, it is found that the upfield γ shielding effect is only operative when the carbon atom, situated γ to the exocyclic oxygen, bears at least one hydrogen. Conformational changes about the arylO bond can be monitored via the vicinal31pOC

ISSN:0030-4921    

DOI:10.1002/mrc.1270190211

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY