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1.
Carbon-13 NMR chemical shifts and one-bond carbon–hydrogen coupling constants have been obtained at 15·09 MHz. The trends in the carbon chemical shifts obtained for the pyrazines parallel those of monosubstituted benzenes and 2-substituted pyridines, except for the direct effect of substitution where the pyrazines resemble pyridines not benzenes. The substituent effects on the 13C NMR spectra are generally quite similar to those in the 1H NMR spectra. The 13C NMR spectrum of the tautomeric hydroxypyrazine has been compared with the 13C NMR spectra of 2-, 3- and 4-hydroxypyridines. Hydroxy compounds that can exist as a cyclic amide show a large meta substituent effect on the chemical carbon shift.  相似文献   

2.
Proton-coupled and noise-decoupled 13C NMR spectra of 1-azulenecarbaldehyde, 1-acetylazulene and 1,3-azulenedicarbaldehyde have been studied, and complete assignments have been made based on the 13C? 1H coupling constants, additivity of substituent effects (SIS), and previous assignment for the parent hydrocarbon. The barriers to rotation of the aldehyde group in the above azulenecarbaldehydes and in some naphthaldehydes have been determined by 13C dynamic NMR, (DNMR), resulting in free energies of activation of 42.7, 26.8 and 34.4 kJ mol?1 for 1-azulenecarbaldehyde, 1-naphthaldehyde and 2-naphthaldehyde respectively. The same order of barriers is obtained by CNDO/2 calculations. A 4-methoxy substituent in 1-naphthaldehyde and a 6-methoxy substituent in 2-naphthaldehyde increases the rotational barrier by 4.6 and 2.9 kJ mol?1, respectively, whereas a 3-methoxy substituent in 2-naphthaldehyde reduces the barrier by 6.7 kJ mol?1. The conformations of the dominant rotamers are deduced from 13C chemical shifts to be Z for 1-azulenecarbaldehyde and 1-naphthaldehyde, and E for 2-naphthaldehyde.  相似文献   

3.
13C n.m.r. spectra of methyl substituted thianes and thianium cations have been determined. The magnitude of the 13C substituent effects of an equatorial methyl group or of a gem-dimethyl grouping appear to depend in a systematic way on whether the carbon atom concerned is adjacent to, or removed from, the heteroatom. The shieldings are discussed in relation to the conformational properties of the thiane ring. Moreover, the average 13C substituent parameters obtained from conformationally biased systems are applied to potentially mobile systems to assess the position of the conformational equilibrium.  相似文献   

4.
13C NMR spectra are reported for derivatives of toxic sesquiterpenes, anisatin (I) and neoanisatin (II). Chemical shifts for each compound have been assigned on the basis of off-resonance decoupling experiments, known chemical shift rules, and comparison of the spectra among the compounds examined. Toxic anisatin (I) is known to isomerize under mild conditions to a non-toxic compound, anisatinic acid. The structure of anisatinic acid has been determined unambiguously to be IIIa by the 13C NMR spectral analysis of a derivative 8 of anisatinic acid. Some aspects of the substituent effects on the 13C chemical shifts obtained in the present investigation are described.  相似文献   

5.
The natural abundance 13C NMR spectra of bromobenzene and ten derivatives have been obtained using the technique of noise modulated decoupling of the proton resonances. Assignments have been made for all 13C resonance signals using an additivity rule. The chemical shifts of the aromatic carbon nuclei in the para-substituted compounds are discussed in terms of the Taft parameters (σR, σI) and the electronegativity of the substituent.  相似文献   

6.
The proton-coupled and proton-decoupled pulsed Fourier-transform 13C NMR spectra of a series of neutral ferrocene derivatives and ferrocenylalkylium ions have been recorded and analysed. The influence of a substituent group upon the 13C shifts of the carbons of the ferrocene rings has been investigated. The spectra of the ferrocenylalkylium ions are discussed in relation to the distribution of positive charge and to the various structural models which have been proposed for such species.  相似文献   

7.
13C NMR spectra of a series of substituted nortricyclene derivatives have been measured, and the 13C chemical shifts interpreted in terms of α, β, γ and δ-effects. The nature of these substiuent shifts is discussed together with some analytical possibilities. The substituent shifts provide valuable data about the steric effects in strained molecules and can be used as increments for structural analysis, particularly for the determination of orientations of substituent groups.  相似文献   

8.
The 13C NMR spectra of the diterpenoid aminoglycoside wedeloside and certain of its derivatives, representatives of a new kaurenoid series, have been assigned. Shift calculations and labelling experiments have established a general substituent additivity relationship for chemical shifts in kaur-16-enes which allowed the reassignment of certain 13C resonances in the previously reported spectra of other kaur-16-enes.  相似文献   

9.
The characteristics of the 1H and 13C NMR spectra of 1,3-oxazolidines with substituents in the 2-, 3-, and 5-positions have been studied. The relation of the spectral characteristics to the structure and configuration of the compounds has been examined, and information on the transmission of the substituent effect through the atoms of nitrogen and oxygen has been obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1255–1260, September, 1986.  相似文献   

10.
13C and 1H nuclear magnetic resonance (NMR) spectra have been obtained in order to identify the six nitration products of pyrene—1-nitropyrene, 1,3-dinitropyrene, 1,6-dinitropyrene, 1,8-dinitropyrene, 1,3,6-trinitropyrene and 1,3,6,8-tetranitropyrene. 13C chemical shifts in DMSO-d6 were assigned using empirical rules, with particular emphasis on the additivity of the substituent effects. Carbon spectra of separated dinitromixtures enabled identification of the previously unreported 1,3-isomer, and proton spectra differentiated the 1,6- and 1,8- isomers.  相似文献   

11.
1H and 13C nmr spectra of several N‐ and C‐substituted carbazoles (Series 1, 2, 3 and 4) were measured. Correlations between chemical shifts and substituent constants show that these parameters describe properly the substituent effect on the nmr phenomena. Atomic charge densities for carbazoles of Series 1, 2, 3 and 4 were calculated by using the semi empirical PM3 method. These values also show a linear correlation with the 13C chemical shifts. The synthesis of several carbazole derivatives 1a – 1g, 2a – 2g, 3a – 3j and 4a – 4g have been carried out according to literature procedures. The carbazoles 3i, 3j and 4c have been synthesized and fully characterized for the first time.  相似文献   

12.
G. Höfle 《Tetrahedron》1977,33(15):1963-1970
Proton coupled and proton noise decoupled 13C-NMR spectra of 18 1,4-napthoquinones and 13 anthraquinones with oxygen, nitrogen and halogen substituents have been measured. The assignment of the spectra was largely achieved with the aid of the two- and three-bond spin-spin coupling between 13C and protons and the substituent effects.  相似文献   

13.
Substituent Effects on NMR Spectra of Pentafulvenes. 13C, 13C-NMR Coupling Constants (1J(C, C)) 1H- and 13C-NMR spectra of 6-monosubstituted pentafulvenes 1 – 8 have been analysed, and 1J(C, C) coupling constants have been determined from ID-inadequate spectra of 13C satellites. It turns out that 13C,13C coupling constants of the ring C-atoms, and especially J(1,2)/J(3,4) and J(2,3), reflect the extent of π delocalisation in the fulvene ring. With increasing electron-donating capacity of the substituent R, J(1,2)/J(3,4) values are decreasing, while J(2,3) (and J(1,5)/J(4,5) as well) are increasing, and linear correlations of Hammett substituent constants σ+ and 1J(C,C) values are obtained.  相似文献   

14.
Proton and carbon-13 chemical shifts of para-substituted stilbenes have been measured. 1H-1H, 1H-13C COSY spectra were obtained to analyze unambiguously the chemical shifts of protons and carbons. A long range coupling between 2-H and α-H was observed in a 1H-1H COSY spectrum. The observed chemical shifts have been correlated with Hammett substituent parameters. Among ethenyl protons and carbons, all but the chemical shifts of α-H show good correlation with both dual substituent parameters and single substituent parameters. In addition to this finding, the excellent linear correlations of C-l, and 4′-H of 4-substituted trans-stilbenes are also reported. Besides the correlations of chemical shifts with Hammett parameters, a good correlation between the chemical shifts and the calculated charges of position C-4′ are reported.  相似文献   

15.
S. Braun  J. Kinkeldei 《Tetrahedron》1977,33(14):1827-1832
The 13C chemical shifts of all possible monomethyl azulenes and of some polymethyl derivatives have been determined by the Pulse Fourier Transform technique and have been assigned on the basis of 13C,H coupling constants and/or splitting patterns taken from proton coupled 13C NMR spectra. The shift differences observed in the monomethyl derivatives as compared to azulene itself are additive as far as sterically unperturbed polymethyl derivatives are concerned and can be viewed on as substituent constants. As is shown by the results of HMO- and EHT-calculations the substituent induced shifts in monomethyl azulenes without sterical hindrance can be correlated with charge density changes, with the exception of the β -effect, which is proportional to the bond length resp. the π bond order.  相似文献   

16.
Methyl and acetyl substituent effects on 13C chemical shift have been determined on (α 1→3), (α 1→4), (β 1→3) and (β 1→4) linked polysaccharides such as pseudo-nigerane, β-cyclodextrine, amylose, laminarane and cellulose. Methyl α- and β-D -glucopyranoside have been used as monomer model compounds. Shift determination of hydroxylated and substituted polysaccharides requires unambiguous assignment of their 13C spectra. Selective heteronuclear spin decoupling and the isotope effect of deuterated hydroxyl have been used as assignment techniques.  相似文献   

17.
Carbon-13 NMR chemical shifts are reported for six angular and one linear dichloropyridoquinolines in CDCl3. The chemical shift assignments have been made using model compounds, fully coupled spectra, selective proton decoupling and results from lanthanide shift studies. Chlorine substituent effects are compared to those reported for chloroquinolines. The effect of the heteroaromatic nitrogen atoms on 13C? 1H coupling constants in these polycyclic systems are compared to those reported for pyridine systems.  相似文献   

18.
The 1H and 13C NMR spectra of a series of 1,3,2-dioxarsolanes have been obtained at 2.1 T and some at 9.4 T. The chemical shifts and spin-spin coupling constants have been obtained from complete spectral analyses of the 1H and proton-coupled 13C spectra. The spectral data are interpreted on the basis of two rapidly interconverting half-chair conformers with a pseudoaxial substituent at arsenic. Unique assignment of syn/anti or cis/trans geometries have been made from 1H or 13C NMR spectroscopy alone. The syn and trans isomers of the 4-methyl- and 4,5-dimethyl-1,3,2-dioxarsolanes, respectively, appear to be conformationally biased towards the forms with pseudoequatorial methyl groups. The general trends in the geminal and vicinal 1H? 1H and 13C? 1H coupling constants are interpreted in terms of stereospecific, electronegativity and lone-pair effects of the oxygen heteroatoms and conformational factors. The NMR data on the 1,3,2-dioxarsolanes are discussed with reference to related 1,3-dithoxa- and 1,3-dithia- five-membered rings with As, P, S or C at the 2-position.  相似文献   

19.
The effects of an hydroxy substituent on 13C? 13C coupling constants and 13C chemical shifts have been measured in 1-hydroxynaphthalene-2-13C and 1-hydroxypyrene-1-13C. The changes observed in the 13C? 13C couplings show the effect of a substituent attached directly to the labelled carbon or to a carbon ortho to this. In both situations the effect is a decrease in the numerical magnitude of most of the long range 13C? 13C coupling constants.  相似文献   

20.
The 13C NMR spectra of forty-six cyclic dithioacetals and their derivatives have been studied. A set of shift parameters was established for each of these heterocycles as substituent. Based on the Hammett type correlation for substituted benzenes, the σP +values of cyclic dithioacetal groups have been determined.  相似文献   

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