ISSN:0749-1581    

DOI:10.1002/mrc.1260310102

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe methylated metallocenes (MeCp)2M with M = V, Cr, Mn, Co, Ni (1–5) were investigated by1H and2H NMR spectroscopy at natural abundance. The2H NMR signals are narrower by a factor of up to 30 compared with the corresponding1H NMR signals, thus establishing an inexpensive method and a general improvement of the NMR spectra of paramagnetic π‐complexes. This has allowed the resolution of the signal splitting of Cp deuterons of 1 and 5 which could not be observed earlier in the1H NMR spectra. The origin of the small (1 and 5) and large (2–4) signal splittings is discussed and related to an extended Hückel calculation. The relative magnitude of the signal splitting is reproduced, but the signal assignment had to be deduced from13C NMR results. Primary isotope shifts of up to 4.0 ppm were found for 1, 2, 4 and 5. The much higher values for 3 (up to 16.6 ppm) reflect the combined influence of the intrinsic isotope shift and the isotope effect on the spin cr

ISSN:0749-1581    

DOI:10.1002/mrc.1260310103

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractSeveral 1‐(2′,4′,6′‐trinitrophenyl)dinitrobenzimidazoles (1‐picryldinitrobenzimidazoles) were synthesized as part of an ongoing study of heterocyclic nitro compounds as energetic materials and their structure–property relationships. The 1‐picryl‐4,6‐dinitrobenzimidazoles and their 1‐methyl analogs were examined by several NMR techniques in order to confirm their structures, and assignment strategies are discussed. Nuclear Overhauser enhancement (NOE) difference spectroscopy and1H/13C correlation experiments were used to make definitive assignments of the1H and13C NMR spectra. It was found that both solvent and temperature had significant effects on the chemical shifts of the benzimidazole protons. This was especially true for the

ISSN:0749-1581    

DOI:10.1002/mrc.1260310104

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractCarbon‐13 NMR spectra were recorded for two series of isoxazolidines, 3 (a 5/5 fused system) and 4 (a 6/5 fused system), over the temperature range − 100 to +60°C. Whereas all the compounds in series 3 existed solely as one isomer throughout this temperature range, some compounds in series 4 showed the presence of two isomers of unequal population at low temperatures. The major isomer was shown to be thetransconformer, which is in equilibrium with the minor isomer (cisconformer) through a relatively slow nitrogen inversion. The monosubstituted isoxazolidines 4 havingendosubstituents at either C‐2 or C‐3 and 2,3‐di‐ and 2,2,3‐trisubstituted compounds showed the presence of only one isomer throughout the temperature range. The barriers to nitrogen inversion were determined by band shape analysis and were in the range 65.2

ISSN:0749-1581    

DOI:10.1002/mrc.1260310105

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractCoupling constants and nuclear Overhauser effect measurements were used to establish the C‐20 configuration and the conformation about the C‐17C‐20 bond in a series of sixteen C‐20‐substituted 5β,14β‐pregn‐14‐enes. In the 14β‐pregnane series the conformation of the C‐17 side‐chain is variable, whereas in the pregnenes the side‐chain adopts a conformation in which H‐17 isantito H‐20. The C‐17 side‐chain conformation of two 21‐nor‐5β,14β‐pregnanes was also determined. In the 21‐nor compounds a C‐20 hydroxyl adopts a conformationant

ISSN:0749-1581    

DOI:10.1002/mrc.1260310106

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractDeuterium isotope effects on13C nuclear shielding,nΔC(OD), were investigated for a large number of substitutedortho‐substituted aromatic hydroxyacyl compounds of the type salicylaldehyde, 2‐hydroxyacetophenone, etc. The isotope effects were analysed as a function of substitution patterns.2ΔC‐2(OD) shows a linear dependence on ΔOH, with one slope for 4‐ and 6‐substituted derivatives and another for 5‐substituted derivatives. A similar pattern is also found for the long range isotope effects. In addition, isotope effects also correlate with13C chemical shifts. Isotope effects ino‐hydroxyacetophenones can be predicted from the δOHandnΔC(OD) values of salicylaldehyde, andvice versa. The isotope effects were analysed in terms of a vibrational term related to the intramolecular hydrogen bond and an electronic term related to the substituent influence on the transmission of the effect along the pathway between the deuterium‐substituted oxygen and the carbon in question.2ΔC(OD) isotope effects are found to depend on the one‐bond bond order of the CC bond of the unsubstituted hydrocarbons. Long‐range isotope effects are observed to the olefinic carbons of 2‐hydroxychalcone, whereas no effects beyond C‐1′ are seen ino‐hydroxyketones oro‐hydroxybenzophenones. The tautomeric equilibrium of usnic acid is perturbed by the removal of the weak hydrogen bond betwe

ISSN:0749-1581    

DOI:10.1002/mrc.1260310107

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of 40 vicinally substituted 2‐ and 3‐nitropyridines were recorded. The observed chemical shifts are, in general, non‐additive. These results are discussed in terms of the effects of 2‐, 3‐ and 4‐substitutents on the ring carbons and of the position of the fixed nitro group and the substituent. The chemical shifts of theparacarbon, with respect to the substitutent, follow well the dual substituent parameter approach, which shows their electronic origin. However, the substituent chemical shifts of bothipsoandorthopositions can be rationalized, in terms of multiple parameter substituent correlation analysis, only on a approx

ISSN:0749-1581    

DOI:10.1002/mrc.1260310108

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractHeteronuclear double and triple resonance experiments of the type1H{X} (X =31P,199Hg,207Pb),13C{1H,31P},29Si{1H,31P},207Pb{1H,31P}, pseudo‐triple resonance experiments [e.g.13C{1H(199Hg)},207Pb{1H(13C)}], together with two‐dimensional (2D)13C/1H heteronuclear shift correlations, were carried out to determine the signs of various coupling constants [1J(M13C),2J(MC13C),3J(MCC13C),3J(MCC1H),4J(MCCC1H); M =29Si,119Sn,207Pb,195Pt,199Hg;3J(195PtCCM); M =29Si,119Sn,207Pb] in 17 alkynyl metal compounds. In all compounds studied, the sign of the reduced coupling constantsnK(M13C) (n= 1, 2, 3) is positive. The same is true for3K(MCC1H) and3K(195PtCCM) (M =29Si,119Sn,207Pb), whereas a negative sign was found for al

ISSN:0749-1581    

DOI:10.1002/mrc.1260310109

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe conformation of ε‐caprolactam (1‐azacycloheptan‐2‐one) was studied by low‐temperature 2 D1H and13C NMR. Only one conformer was found in solution from the13C NMR spectra recorded down to −155°C. This conformer was shown, by infrared spectroscopy, to be the same as that found in the crystals of ε‐caprolactam. A conformational process with a free energy of activation of 43 kJ mol−1, coalescence temperature −65°C, was interpreted as geminal1H exchange. The assignments of the13C and1H shifts were made by 2 D NMR. Splitting of all averaged signals for geminal protons into axial and equatorial signals was d

ISSN:0749-1581    

DOI:10.1002/mrc.1260310110

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractIsotope effects on the chemical shift of13C directly bonded to the isotopes35Cl and37Cl are reported for a wide range of chlorohydrocarbons. By recording13C NMR spectra under conditions of composite pulse1H decoupling,13C resonances can be obtained that are sufficiently narrow to allow the very small splittings of the order of a few ppb due to the35Cl/37Cl isotope effect to be resolved at ambient temperature. Observation of this phenomenon allows the routine identification of13C resonances due to carbon atoms directly bonded to chlorine, since, for natural abundance samples, the isotope effect splits the13C signal into a set of lines with a characteristic intensity distribution. Various structural features influencing the magnitude of the isotope effect have been elucidated, and the temperature dependence of the isotope effect is also discussed. From low‐temperature13C NMR spectra for chlorocyclohexane, isotope shifts for the carbon atom directly bonded to chlorine were measured separately for the axial and equatorial conformations. The measured values indicate that the isotope shift is larger for the axial conformatio

ISSN:0749-1581    

DOI:10.1002/mrc.1260310111

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY