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1.
The proton NMR spectral analysis of eight different 1,3,2-dithiaphospholanes with various groups attached to the phosphorus atom has been performed. The AA′BB′X (X phosphorus atom) system shows that the two 3J(P? S? C? H) coupling constants have a small magnitude and opposite signs. Using the 3J(HH) values, the torsion about the C4—C5 bond has been evaluated. The conformational requirements in the two isomers of the 2 phenyl-4-methyl-1,3,2-dithiaphospholane are also discussed.  相似文献   

2.
The signs of the phosphorus-proton coupling constants in various allenic organophosphorus compounds have been determined by either analysis of the AB2X spectra or double resonance. Probable absolute signs have been obtained by taking 3J(P? H) as positive. In allenic phosphine oxides, the following signs are obtained: 2J(P? H) +ve, 3J(P? H) +ve, 4J(P? H) ?ve, 5J(P? H) +ve and the 4J(P? H) coupling constant varies mostly with the inductive effect of the substituents bound to the phosphorus atom. In allenic phosphines, these sings are: 2J(P? H) +ve, 3J(P? H) +ve, 4J(P? H) ?ve and +ve and the 4J(P? H) coupling constant varies with both the inductive and resonance effects to the substituents. This coupling constant is negative except when the phosphorus atom is bound to groups which are electron-donating by resonance effects. These results are discussed in relation to the pπ? dπ bonding in phosphine.  相似文献   

3.
Reactions of Mononucleophiles with a Bromoenurononitrile, Precursor and Partial Synthetic Equivalent of an Ynurononitrile Several mononucleophiles (bases) have been reacted with one or the other of the geometrical isomers of the bromoenurononitrile 1. Depending on the nucleophile and the conditions, many different mechanistic pathways were followed, f. ex.: with OH?, stereospecific elimination from (Z)- 1 leading to 2 , with N?3 and F?, stereospecific E-AN reactions leading from (Z)- 1 to (Z)- 8 and (Z)- 12 respectively, with PhCH2SH, conjugate nucleophilic addition to 7, with Me2NH, conjugate nucleophilic addition followed by a SN2 to 11 , as well as several cases of nonstereoselective, probably AN-E, reactions leading to 3,6,9 and 10. In spite of their diversified reactivity, bromoenurononitriles like 1 , partial synthetic equivalent of 2 , constitute useful synthetic intermediates.  相似文献   

4.
The NMR parameters are determined for a series of disubstituted (R = CH3, (CH3)3C; X = COOCH3, CN) and specifically deuterated cyclohexenes. The 3 J(HH), 3J(HD), 4J(HH) and 5 J(HH) coupling constants are used to evaluate the conformational equilibria. Three of the five compounds with an allylic t-butyl substituent, are conformationally heterogeneous; these equilibria, and those between stereoisomers are used for an analysis of this phenomenon, carried out within the framework of the hypothesis of additivity of conformational free energies and gauche interactions.  相似文献   

5.
All J(P? H) and J(P? C) values, including signs, have been obtained in acetylenic and propynylic phosphorus derivatives, R2P(X)? C?C? H and R2P(X)? C?C? CH3 (X ? oxygen, lone pair and R ? C6H5, N(CH3)2, OC2H5, N(C6H5)2, Cl) from 1H and 13C NMR spectra. In PIV derivatives the following signs are obtained: 1J(P? C)+, 2J(P? C)+, 3J(P? C)+, 3J(P? H)+, 4J(P? H)? . Linear relations are observed between 1J(P? C), 2J(P? C) and 3J(P? C) versus 3J(P? H), indicating that these coupling constants are mainly dependent on the Fermi contact term, though the other terms of the Ramsey theory do not seem to be negligible for 1J(P? C) and 2J(P? C). In PIII derivatives these signs are: 1J(P? C)- and +, 2J(P? C)+, 3J(P? C)-, 3J(P? H)-, 4J(P? H)+. Only 3J(P? C) and 3J(P? H) reflect a small contribution of the Fermi contact term while in 1J(P? C) and 2J(P? C) this contribution seems to be negligible relative to the orbital and/or spin dipolar coupling mechanisms.  相似文献   

6.
The orientation of the cycloaddition of diazomethane on unsaturated branchedchain sugars has been studied. For 3-C-cyanomethylidene-3-deoxy-1,2-O-isopropylidene-α-D-glycero-tetrofuranose the orientation was ‘normal’ and did not depend on the configuration at the double bond. The same situation prevailed with derivatives of 3-deoxy-1,2:5,6-di-O-isopropylidene-3-C-methylidene-α-D-xylo-hexofuranose. For the 3-C-acylmethylidene- and the 3-C-cyanomethylidene-3-deoxy-1,2:5,6-di-O-isopropylidene-α-D-ribo-hexofuranoses, the trans-(H–C(3′)–C(2))-isomer gave the ‘normal’ cycloadduct whereas the cis-isomer gave predominantly the αabnormal spiro-pyrazoline. This observation represents the first instance where the regioselectivity of a cycloaddition reaction is affected by the geometrical isomerism of the dipolarophile. The most probable explanation of the phenomenon is the conformational perturbation about the C(4)--C(5) bond of the unsaturated sugars induced by a change in the configuration at C(3). The consequence of that ‘conformational transmission’ of a difference in configuration at C(3) is that the steric crowding on the cis- than in the trans-isomer. Several novel examples of a new series of C-glycosylidenic derivatives, the spiro-pyrazolines, are described.  相似文献   

7.
Coupling between P and (N)? H has been observed in the 1H{14N}NMR spectra of a series of phosphorus substituted thioformamides, R12/P(X)C(S)NHR2. For R2 = H one of the two couplings constants 3J(PCNH) is much larger than the other. The larger constant is assumed to be 3J(PCNH) (trans) and the magnitude of 3J(PCNH) for several compounds with R2 = Me or Ph is used to assign the configuration about the C(S)? N bond.  相似文献   

8.
Novel types of acetylenic sugars The coupling, following Cadiot's procedure, of a 6-bromo-5,6-dideoxy-1,2-O-isopropylidène-3-O-methyl-α-D -xylo-hex-5-yno-1, 4-furanose (1) with phenylacetylene, 2-propyn-1-ol or terminal acetylenic sugars gave with excellent yields the expected diynes (an enediyne when the terminal acetylene was the 3,5, 6-trideoxy-1,2-O-isopropylidene-α-D -glycero-hex-3-en-5-yno-1,4-furanose 7 ). The chloro analogue 8 of 1 on treatment with lithium thiophenate gave the corresponding phenylthio-acetylenic sugar 9 . An acetylene was also formed by reacting the gem-difluoro-olefinic sugar 10 with butyllithium whereas the same olefinic sugar and its 3-O-benzyl analogue 11 gave only a gem-fluoro-arylthio-olefinic sugar (13–15) as a mixture of the Z and E isomers (Z/E > 4) when treated with the conjugate base of an arylmercaptan.  相似文献   

9.
The 1H NMR spectra of several 1,3,2-dioxaphosphorinanes bearing an extracyclic P? N bond have been analysed. The 3J(POCH) couplings are strongly dependent upon the orientation of the bond around the phosphorus atom. Depending upon the nature of the bonds attached to the nitrogen atom, the dioxaphosphorinane ring may adopt either a fixed chair conformation with the P? N bond in the axial or equatorial orientation, or it may be in equilibrium between two chair conformations where the P? N bond is alternately axial or equatorial. The equilibrium is fast on the NMR time scale.  相似文献   

10.
INDOR experiments indicate 4J(P? C? C? O? H) to be positive for the β-hydroxyphosphonate ester RS,RS dissolved in (CD3)2CO or (CD3)2SO. The higher value observed in (CD3)2SO than in (CD3)2CO shows that a W geometry makes this coupling constant more positive.  相似文献   

11.
The treatment of the 1, 2:5, 6-di-O-isopropylidene-α-D -ribo- and xylo-hexofuranos-3-uloses with cyanomethylenetriphenylphosphorane led in each case, and in almost quantitative yields, to a pair of geometrical isomers of C-cyanomethylenic sugars having respectively the ribo and the xylo configurations. Permanganate oxidation of these branched-chain unsaturated sugars afforded the corresponding gem-hydroxyformyl compounds bearing the formyl group on the more hindered face of the molecule. The formyl group of these sugars is easily derivatized to an oximino or reduced to a hydroxymethyl. The configuration at the new asymmetric carbon has been established by comparison with known compounds or by synthesis of a C(3) epimer by the classical route involving a Grignard reagent.  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.
Proton–proton 3J, 4J and 5J NMR coupling constants have been calculated for cyclohexane and monosubstituted cyclohexane conformers (substitiuents: Li, CH3, OH, F) by the two methods mentioned. Comparing the two methods on the basis of group theory, we show the necessity to use the second. The results from this method are compared with those of the literature.  相似文献   

14.
We present a method to use long‐range CH coupling constants to derive the correct diastereoisomer from the molecular constitution of small molecules. A set of 79 2JCH and 3JCH values collected from a single HSQMBC experiment on a sample of strychnine were used in the CASE‐3D (computer‐assisted 3D structure elucidation) protocol. In addition to the most commonly used 3JCH coupling constants, the subset of 32 2JCH values alone showed an excellent degree of configuration selection. The study is mainly based on comparison of DFT‐calculated 2,3JCH values with experimental ones, critical for the case of 2JCH. But the configuration selection also works well using 3JCH values predicted from a semi‐empirical Karplus‐based equation limited to H?C?C?C fragments. The robustness, shown using strychnine as a proof of concept, makes the J‐based CASE‐3D analysis a viable option for the application in fields such as peptide and carbohydrate research, organic synthesis, natural‐product identification and analysis, as well as medicinal chemistry.  相似文献   

15.
By PMR, three dioxane–Li+ complexes have been detected for the oligopolyisoprenyl–lithium–dioxane mixtures in benzene solution. The (4-1) living end isomerizes into the cis configuration when the sample temperature or the dioxane concentration is increased, but the isomerization phenomenon is reversible only if dioxane/Li+ ratios are smaller than unity. The specificity of the vinyl addition (86%), mainly (4-3) (70%), due to the stronger negative charge at the Cγ carbon atom is effective only at low temperature (+15°C). At higher temperature, because of the steric hindrance of the methyl group, this stereospecificity decreases.  相似文献   

16.
Some monomer model compounds of lignin have been selectively 2H and 13C labelled: vanillin, ethyl ferulate, coniferyl alcohol and ethyl hydrogen malonate. Deuterium isotope effects on the 13C chemical shifts in [formyl-2H]vanillin, [5-2H]vanillin and [α,α,5-2H3]coniferyl alcohol made the unambiguous assignment of the aromatic 13C signals possible. Absolute 1,2,3J(CC) values have been determined on 13C spectra of [formyl-13C]vanillin, and of ethyl ferulate and coniferyl alcohol in which the vinylic C-γ and C-β carbons were 13C enriched. It has been possible to measure 4J(C?O, C-4) in vanillin and 4J(C-γ, C-4) in ethyl ferulate. The determination of 1,2,3,4J (CH) absolute values was done by means of gated decoupled 13C spectra of the non-labelled compounds. When second order effects made the use of this technique impossible we determined certain J(CH) values and their signs either by analysing the 1H NMR spectra of 13C labelled coniferyl alcohol [2J(C-β, H-γ), 2J(C-β, H-α), 2J(C-γ, H-β), 3J(C-γ, H-α)] or by a double irradiation experiment on the 250 MHz 1H NMR spectrum of ethyl [β-13C] ferulate [for 2J(C-β, H-γ)].  相似文献   

17.
The four pseudoprotoberberins extracted from Isopyrum thalictroides L. were reduced with sodium borohydride to the corresponding tetrahydropseudoprotoberberins. Comparison between the 13C NMR spectra of these and of synthetic protoberberins allowed us to assign a trans-1 configuration to the four reduced alkaloids and also to provide for this particular configuration an unequivocal criterion for the differentiation (based on the chemical shift of C-8) between tetrahydroprotoberberins (9, 10 substituted) and tetrahydropseudoprotoberberins (10, 11 substituted).  相似文献   

18.
A Novel Example of Reversible Ring Opening: The Epimerization at C(3) of Sugar 3-Hydroxy-Δ1-pyrazolines Reaction of 1 (either geometrical isomer) with hydrazine followed by in situ Ag2O oxidation led to two pairs of interconverting isomers 4 ? 5 and 6 ? 7 . By the same treatment, (Z)- 10 and (or) (E)- 10 gave the pair 11 ? 12 . Acetylation of 4 ? 5 led to a non interconverting mixture of 8 and 9 . This fact, and the lack of incorporation of 18O when the epimerization took place in the presence of H218O indicated that the most probable mechanism consisted in a reversible ring opening ( D ? E ? F ). The kinetic parameters of these reactions are given and structural assignments proposed for the new compounds.  相似文献   

19.
Several 1:1 adducts of gallium trihalides with triarylphosphines, X3Ga(PR3) (X=Cl, Br, and I; PR3=triarylphosphine ligand), were investigated by using solid‐state 69/71Ga and 31P NMR spectroscopy at different magnetic‐field strengths. The 69/71Ga nuclear quadrupolar coupling parameters, as well as the gallium and phosphorus magnetic shielding tensors, were determined. The magnitude of the 71Ga quadrupolar coupling constants (CQ(71Ga)) range from approximately 0.9 to 11.0 MHz . The spans of the gallium magnetic shielding tensors for these complexes, δ11?δ33, range from approximately 30 to 380 ppm; those determined for phosphorus range from 10 to 40 ppm. For any given phosphine ligand, the gallium nuclei are most shielded for X=I and least shielded for X=Cl, a trend previously observed for InIII–phosphine complexes. This experimental trend, attributed to spin‐orbit effects of the halogen ligands, is reproduced by DFT calculations. The signs of CQ(69/71Ga) for some of the adducts were determined from the analysis of the 31P NMR spectra acquired with magic angle spinning (MAS). The 1J(69/71Ga,31P) and ΔJ(69/71Ga, 31P) values, as well as their signs, were also determined; values of 1J(71Ga,31P) range from approximately 380 to 1590 Hz. Values of 1J(69/71Ga,31P) and ΔJ(69/71Ga,31P) calculated by using DFT have comparable magnitudes and generally reproduce experimental trends. Both the Fermi‐contact and spin‐dipolar Fermi‐contact mechanisms make important contributions to the 1J(69/71Ga,31P) tensors. The 31P NMR spectra of several adducts in solution, obtained as a function of temperature, are contrasted with those obtained in the solid state. Finally, to complement the analysis of NMR spectra for these adducts, single‐crystal X‐ray diffraction data for Br3Ga[P(p‐Anis)3] and I3Ga[P(p‐Anis)3] were obtained.  相似文献   

20.
The purpose of this study was to gain a closer knowledge of the molecular constitution of the linear fluorine-terminated oxygen-bridged methylphosphanoxy/dimethylsilane polymers, for example, to find evidence for preferential sorting (or, on the contrary, for random scattering) of the substituents and building units. The title polymers were prepared by reaction of MeP(O)F2 with cyclic dimethylsiloxanes (Me2SiO)n (n = 3 or 4). An equilibrium is reached in the redistribution of fluorine vs. bridging oxygen atoms among the phosphorus and silicon-based centers, and among the resulting building units, after about 2 months at 120°C. The excellent resolution of the 1H-NMR spectra (Fig. 2), even at 60 MHz, allowed identification of seventeen different fragments (Table II). Nineteen equilibrated samples of varied overall compositions (R = F/(Si + P); R′ = P/(Si + P)) have been analyzed (Table IV), and their molecular constitution is described by a set of four basic constants. The fundamental features which govern the structure of these polymers are as follows. (a) The regular (Si-O-P) alternation of the two different centers, which is thermodynamically favored, as shown by the linkage constant K0 = [Si-O-Si][P-O-P]/[Si-O-P]2 ? 104, which describes the sorting of the silicon and phosphorus atoms on the bridging oxygens, and which deviates by four orders of magnitude from its random value of 0.25. (b) A somewhat surprising lack of preferential distribution of fluorine and oxygen between the two centers (KI = [MeP(O)F2][Me2SiO1/2]2/[Me2SiF2]-[MeP(O)(O1/2)2]) differs little from (a), which contrasts with the preferential affinity of fluorine for silicon and oxygen for phosphorus (KI ? 107) that was found when F atoms and OCH3 groups were exchanged between the same centers. (c) The sorting of the fluorine atoms and oxygen bridges on each center, to give neso molecules and the terminal and medium building units, resulting in a slight preference for the formation of the terminal units, as expressed by   相似文献   

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