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1.
17O-NMR. Aliphatic aldehydes and ketones, additivity of substituent effects and correlation with 13C-NMR. The 17O-chemical shifts of 9 aldehydes, 22 aliphatic and 4 alicyclic ketones, in the natural abundance FT.-NMR. spectra followed a good correlation with the 13C-chemical shifts of the terminal C-atoms of corresponding methylene compounds. An additivity relation involving 6 parameters represents the 17O-shifts of 28 of the measured products with a standard deviation of 2.5 ppm. The additivity parameters are discussed with respect to the modifications of the polarity of the carbonyl group induced by the hyperconjugative interaction of π and π* orbitals with the πCH 3 orbitals of the alkyl substituent groups.  相似文献   

2.
Linear relationships between the inverse of the quadrupolar coupling constant, 1/χ and the asymmetry parameter η are obtained for the 7O-nucleus of acetone oriented in four different nematic phases, using the information contained in 1H- and 17O-NMR spectra. The absence of a unique intersecting point of thee relations shows that the quadrupolar constants differ slightly between polar and apolar nematic phases, while the orientation remains similar. By combination of the experimentally derived relations with predictions from the theory of Townes and Dailey, values for χ = 11.15 MHz and η = 0.47 in polar media and χ = 11.35 Mhz and η = 0.15 in an apolar medium are obtained, which are similar to those found in the gas and solid phases.  相似文献   

3.
The 13C- and 17O-chemical shifts of 31 aliphatic ethers are measured and discussed. The 17O-chemical shifts of the ethers ROR′ correlate with chemical shifts for the methylene groups of the corresponding alkanes RCH2R′. The constant of proportionality can be related to the orbital expansion term 〈r?32p. The δc for carbon atoms can also be correlated with δc for the corresponding alkanes. The origin of the correlation is discussed taking into account the conformational modifications resulting from introduction of an oxygen atom in an alkyl chain.  相似文献   

4.
The 13C NMR parameters of 3-O-acetyl-1,2:5,6-di-O-isopropylidène-α-D-[U-13C] glucofuranose, used as a sample for analysis in double labelling biosynthetic experiments, have been measured. Homonuclear double resonance experiments 13C? {13C} at 62.8 MHz have permitted the determination of all the 13C? 13C coupling constants. By theoretical computation of spectra, in connection with the second order effects existing at 25.2 MHz and 15.08 MHz, the sign of the coupling constants has been determined. The theoretical computation of spectra took into account all the isotopomers and was calculated with the help of a program (adapted from the LAOCOON program) allowing for the weighted addition of the spectra.  相似文献   

5.
Carbon-13 NMR spectra of various aliphatic ketones and thioketones were determined and interpreted. As shown by the relation between 13C chemical shifts in C=A groups, the C=S is more sensitive to the substituents than the C=O group. Conjugative effects are more pronounced in α-cyclopropyl thioketones than in α-cyclopropyl ketones.  相似文献   

6.
Studies in Stereochemistry XIV. Diels-Alder adducts in the resin series; action of peracids and acid-catalysed ring opening of epoxides The synthesis of Diels-Alder compounds of type 2 with a 17-nor-13(14)-atisène skeleton is described (cf. Schemes 1–3). Depending on the nature and configuration of substituents R1 and R2 on the carbon atoms 15 and 16, an epoxide ( 24–33 ) or a ketone ( 35–38 ) or a mixture of epoxide, ketone and lactone is obtained by the action of p-nitroperbenzoic acid on the double bond of these adducts (cf. Scheme 4). A simplified reaction scheme is suggested to explain the formation of the various products. In an acid-catalysed reaction, the epoxides isomerize mainly into ketones. Nevertherless, in some cases, dienes (e.g. 52 ) or hydroxy-γ-lactones of (13R*, 14S*)-configuration (e.g. 50 ) resulting from the opening of the epoxide ring with retention of configuration were obtained.  相似文献   

7.
The cleavage of a single SO2? O bond occurs during the polarographic reduction of a tosyloxy group (p? CH3C6H4SO2O = TsO) in aprotic medium and intramolecular cyclisation may ensue when a second TsO group is present on the same molecule. The polarographic behaviour of aliphatic ditosyloxy derivatives is discussed on the assumption that oriented vicinal derivatives at the interface assume a conformation which resembles the geometry of the transition state for an intramolecular elimination with anchimeric assistance of one of the tosyloxy groups. This situation favours the electron transfer, whereas the same geometric requirements hinder the intramolecular interaction of the TsO groups of the oriented non-vicinal derivatives. This interpretation agrees well with the fact that the large scale electrolysis of vicinal ditosyloxy derivatives give much higher yield of cyclic ethers than the higher homologues. It is also shown that intramolecular interaction between TsO groups can occur through an intervening double bond in a non-vicinal derivative.  相似文献   

8.
In 8- and 9-membered cyclic ketones, transannular interactions of an EtN group or an O atom shift considerably the 17O signal of the carbonyl group to higher fields; S appears to have no such effect. The same ketones show markedly diminished speeds of water addition, compared to simple ketones; this reaction was followed by measuring the rate of oxygen exchange between 17O-labelled ketones and (unenriched) water. Transannular interaction inhibits completely in N-ethyl-azacyclodecane-6-one the exchange reaction, including labelling attemps.  相似文献   

9.
A series of 12-alkyl tricosanes (four compounds) was examined by use of 13C nuclear magnetic resonance at 62,89 MHz as model compounds for isolated short- and long-chain (C5, C6, C7, C8) branches in low-density polyethylene and ethylene-α olefin copolymers. An array of 13C resonances was observed and we note that the 13C chemical shifts became insensitive to branch length with octyl and longer branches at this field.  相似文献   

10.
35Cl nuclear quadrupole resonance spectra of cyclic α-chloro ethers of known configuration are presented. The resonance frequencies of chlorine atoms in equatorial positions are in every case some 2.5 MHz higher than those of corresponding chlorine atoms in axial positions. Similar results are obtained for open-chain trichloromethyl ethers and the effect is sufficiently well-defined to distinguish between configurational isomers and establish their conformation. These results may be rationalised in terms of a model in which the lone-pair electrons on the oxygen atom hyperconjugate with the electrons of the C? Cl bond.  相似文献   

11.
《Chemphyschem》2006,7(1):117-130
Ultra‐wideline 27Al NMR experiments are conducted on coordination compounds with 27Al nuclei possessing immense quadrupolar interactions that result from exceptionally nonspherical coordination environments. NMR spectra are acquired using a methodology involving frequency‐stepped, piecewise acquisition of NMR spectra with Hahn‐echo or quadrupolar Carr–Purcell Meiboom–Gill (QCPMG) pulse sequences, which is applicable to any half‐integer quadrupolar nucleus with extremely broad NMR powder patterns. Despite the large breadth of these central transition powder patterns, ranging from 250 to 700 kHz, the total experimental times are an order of magnitude less than previously reported experiments on analogous complexes with smaller quadrupolar interactions. The complexes examined feature three‐ or five‐coordinate aluminum sites: trismesitylaluminum (AlMes3), tris(bis(trimethylsilyl)amino)aluminum (Al(NTMS2)3), bis[dimethyl tetrahydrofurfuryloxide aluminum] ([Me2‐Al(μ‐OTHF)]2), and bis[diethyl tetrahydrofurfuryloxide aluminum] ([Et2‐Al(μ‐OTHF)]2). We report some of the largest 27Al quadrupolar coupling constants measured to date, with values of CQ(27Al) of 48.2(1), 36.3(1), 19.9(1), and 19.6(2) MHz for AlMes3 , Al(NTMS2)3 , [Me2‐Al(μ‐OTHF)]2 , and [Et2‐Al(μ‐OTHF)]2 , respectively. X‐ray crystallographic data and theoretical (Hartree–Fock and DFT) calculations of 27Al electric field gradient (EFG) tensors are utilized to examine the relationships between the quadrupolar interactions and molecular structure; in particular, the origin of the immense quadrupolar interaction in the three‐coordinate species is studied via analyses of molecular orbitals.  相似文献   

12.
From a carbon magnetic resonance study of several alkylcobaloximes RCo(DMG)2B (DMG = dimethylglyoximate monoanion), it was possible to estimate the α, β and γ effects of the Co(DMG)2B group on the chemical shifts of the carbon atoms of various alkyl groups R. The chemical shifts of the carbon atoms belonging to the equatorial ligands and to the axial base B are not significantly affected by structural modification of the R groups. Values of δ in benzylcobaloximes XC6H4CH2Co(DMG)2B agree with a donor effect of the ? CH2Co(DMG)2B radical. Values of 1J(13C? H) coupling constants, measured in 13C enriched methylcobaloximes, do not vary appreciably when B is changed (J(13C? H) = 137 ± 1 Hz) and are close to the value obtained for methylcobalamine.  相似文献   

13.
Unusual behaviour was observed in the study of the 17O, 13C and 1H NMR and IR spectra of crowded (1‐adamantyl)alkyl ketones. As the size of the alkyl substituent is increased, abnormal upfield chemical shifts in the 13C NMR and downfield shifts in the 17O NMR of the carbonyl group, as well as downfield shifts in the 1H NMR of the adamantyl γ'‐protons, are found. In the IR spectrum, the νC?O stretching frequencies of the ketones with bulky substituents show considerable red shifts. Correlation of the NMR shifts with the number of γ‐carbon atoms of the alkyl substituents and comparison with the IR results indicated that there is an intramolecular through‐space CH···O interaction in crowded ketones. This was supported by the results of ab initio calculations. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

14.
The density matrix of a spin S = 9/2 excited by a radiofrequency pulse is calculated. The interaction involved during the excitation of the spin system is first‐order quadrupolar. Consequently, the results are valid for any ratio of the quadrupolar coupling ωQ to the pulse amplitude ω1. The behavior of the central transition intensities versus the pulse length is discussed. The 115In and 113In nuclei in a powdered sample of indium phosphide (InP) are used to illustrate the results. It is found that the ratio of the quadrupolar coupling constants determined in this work is in excellent agreement with the ratio of the quadrupole moments of the two nuclei. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

15.
Pyridinium chloride and bromide react with 1,6-hexanediol through a complex multireactional chain process mostly furnishing unsaturated hydrocarbons, cyclic ethers, unsaturated halides and unsaturated alcohols. The similar transformations undergone by 5-hexene-1-ol and 1-hexanol under the same conditions suggest several hypotheses about the mechanism. Several original assignments from 13C NMR data were involved in determining the structures of the products.  相似文献   

16.
The 13C and 1H spectra of a series of aromatic ketones, ethers and keto-ethers were studied using the lanthanide shift reagent (LSR) Yb(fod)3 and the data analyzed using the lanthanide induced shift (LIS) ratio method. Studies were carried out on phenalenone, 6-methoxyphenalenone, 1- and 2-methoxynaphthalene, 1-indanone, 5- and 6-methoxy-1-indanone and flavone and the data obtained subjected to LSR-substrate geometry analysis as a means of making 13C assignments. The utility and limitations of the LSR method for making 13C assignments is discussed and the LIS ratio method for LSR-substrate geometry analysis is described in detail.  相似文献   

17.
Hydrosilylation of saturated and α,β-unsaturated carbonyl compounds by heterogeneous catalysis without solvent and in the presence of salts (HCO2K, o-Ph(CO2K)2, FK, FCs) was carried out with good yields. FCs is a very efficient salt for hydrosilylation of aldehydes and ketones: for instance α-NpSiH3 reacts quantitatively at room temperature with PhCOPh giving α-NpSi(OCHPh2)3. With α,β-unsaturated ketones FCs leads to 1,2-addition. It allows the isomerization of allysilyl ethers in silyl enol ethers, providing that the transferring hydrogen is benzylic.  相似文献   

18.
Versatile procedures for the preparation of the title compounds are described. Representatives of ketones ( 12 and 27 ), hydrocarbons ( 19 and 28 ), acids ( 13 ), esters ( 15 . and 20 ), ethers ( 22 ) and nitriles ( 18 ) possess wide-range nematic phases, provided their terminal chains R2 and R3 contain at least three methylene units.  相似文献   

19.
A visible-light-induced palladium-catalyzed Dowd–Beckwith ring expansion/C–C bond formation cascade is described. A range of six to nine-membered β-alkenylated cyclic ketones possessing a quaternary carbon center were accessed under mild conditions. Besides styrenes, the electron-rich alkenes such as silyl enol ethers and enamides were also compatible, providing the desired β-alkylated cyclic ketones in moderate to good yields.

An intermolecular Dowd–Beckwith ring expansion/C–C bond formation is achieved through light-induced palladium catalysis. Not only styrenes but also the electron-rich alkenes such as silyl enol ethers and enamides were also compatible in this reaction.  相似文献   

20.
The 17O and 13C chemical shifts (δ) of 14 α,β-unsaturated aldehydes and ketones and 33 acyl derivatives RXC = O (X = Cl, OH, OMe, OEt, NH2 and R = H or alkyl) have been measured. In the unsaturated carbonyl series, a correlation exists between δ 17O and the π electron density at the β-carbon atom. From this correlation, an δ 17O of 530 ppm was extrapolated for the loss of one electron at the oxygen atom. In the acyl series, the δr 17O were also sensitive to changes in the polarity of the carbon-oxygen bond. A partial correlation between 17O-NMR. chemical shifts and the nuclear quadrupole coupling constants exists for aldehydes, ketones, esters and amides but not for acyl chlorides.  相似文献   

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