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1.
In the electron impact mass spectra of some alkyl α- and β-hydroxyesters (introduced using the gas chromatography/mass spectrometry (GC/MS) technique), the absence of the molecular ion M and the presence of the [M + 1]+ ion instead is observed. This phenomenon is especially characteristic of C3? C6 glycolates and diethyl malate, and is due to chemical auto-ionization—ion-molecule reactions in the high concentration gradient at the top of the GC peak. The existence of the [M ? 2], [M ?1]+ and M ions in the mass spectra of other β- and α-hydroxyesters is discussed.  相似文献   

2.
In the title compound, C29H42O4·H2O, cyclo­hexane rings A and B are in the sofa conformation, ring C is in a chair conformation and the five‐membered ring D is in an envelope conformation. The structure is stabilized by inter‐ and intramolecular C—H?O and O—H?O hydrogen bonds.  相似文献   

3.
Synthesis of Diastereo- and Enantioselectively Deuterated β,ε-, β,β-, β,γ- and γ,γ-Carotenes We describe the synthesis of (1′R, 6′S)-[16′, 16′, 16′-2H3]-β, εcarotene, (1R, 1′R)-[16, 16, 16, 16′, 16′, 16′-2H6]-β, β-carotene, (1′R, 6′S)-[16′, 16′, 16′-2H3]-γ, γ-carotene and (1R, 1′R, 6S, 6′S)-[16, 16, 16, 16′, 16′, 16′-2H6]-γ, γ-carotene by a multistep degradation of (4R, 5S, 10S)-[18, 18, 18-2H3]-didehydroabietane to optically active deuterated β-, ε- and γ-C11-endgroups and subsequent building up according to schemes \documentclass{article}\pagestyle{empty}\begin{document}${\rm C}_{11} \to {\rm C}_{14}^{C_{\mathop {26}\limits_ \to }} \to {\rm C}_{40} $\end{document} and C11 → C14; C14+C12+C14→C40. NMR.- and chiroptical data allow the identification of the geminal methyl groups in all these compounds. The optical activity of all-(E)-[2H6]-β,β-carotene, which is solely due to the isotopically different substituent not directly attached to the chiral centres, is demonstrated by a significant CD.-effect at low temperature. Therefore, if an enzymatic cyclization of [17, 17, 17, 17′, 17′, 17′-2H6]lycopine can be achieved, the steric course of the cyclization step would be derivable from NMR.- and CD.-spectra with very small samples of the isolated cyclic carotenes. A general scheme for the possible course of the cyclization steps is presented.  相似文献   

4.
The fragmentations of two α,β-unsaturated γ-dilactones in a mass spectrometer are studied. The main feature is conecutive carbon monoxide expulsions. Strong indication of ejection of a fragment C2O2 is presented, however. Masses were determined by the high resolution rechnique and metastable transitions were detected by defocusing. Corresponding deuterated dilactones were also studied to verify the fragmentation mechanism.  相似文献   

5.
β-Styryl isocyanate (1, R ? H) and its β-methyl- (1, R ? CH3) and β-phenyl- (1, R ? C6H5) derivatives underwent both extensive polymerization and the loss of the elements of carbon monoxide upon irradiation at 254 nm in cyclohexane. The formation of 2,5-diphenylpyrazine ( 3 ) and indole 4 , (R ? H) from 1 , (R - H) and 2,3-dimethyl-5,6-diphenylpyrazine ( 6 ) and 2-methylindole ( 4 , R ? CH3) from 1 , (R ? CH3) provided diagnostic evidence for styryl nitrene ( 2a ) intermediates. The formation of both phenylacetonitrile ( 5 , R ? H) and α-phenylpropio-nitrile ( 5 , R ? CH3) was assigned to an initial rearrangement of the residue, C8H6(R)N?: ( 2 ), into a ketenimine concerted with the elimination of carbon monoxide from 1. Isomerization then produced a nitrile. β3-(β-phenyl)styryl isocyanate ( 1 , R ? C6H5) gave no product requiring the intermediacy of a nitrene and/or an azirine. The formation of 2,3,4,5-tetraphenylpyrrole ( 8 ) was assigned to a dimerization of the isocyanate concerted with or following the elimination of the elements of carbon monoxide and isocyanic acid, and the formation of 3-phenylisocarbo-styril ( 9 ) was assigned to a ring-closure of the isocyanate in an excited triplet state. Each isocyanate gave stilbene and trace amounts of oxidative fragmentation into benzaldehyde and benzonitrile. Solvent participation produced benzylcyclohexane and bicyclohexyl. Two unidentified solids, C17H14N2O and C12H14N2O, were obtained from 1 , (R ? CH3).  相似文献   

6.
Electron impact studies on eight α,β-unsaturated carbonyl oximes revealed many interesting hydrogen and skeletal rearrangements which were substantiated by deuterium labelling, exact mass measurements and metastable studies. Loss of H· and OH· as well as formation of the indenyl and fluorenyl cations and the [C9H6N]+ fragment proceed through cyclic intermediates. All the ionized oximes undergo a Beckmann rearrangement in the gaseous phase leading to intense aroyl cation peaks. Formation of the styrene radical ions and cleavage of the bond α to the oxime function have also been noticed.  相似文献   

7.
The steric structure of poly(methyl propenyl ether) obtained by cationic polymerization was studied by NMR spectra. From the analysis of β-methyl and α-methoxyal spectra, it was found that the tacticities of the α-carbon were different from those of the β-carbon in all polymers obtained. In the crystalline polymers obtained from the trans isomer by homogeneous catalysts, BF3·O(C2H5)2 or Al(C2H5)Cl2, and from the cis isomer by a heterogeneous catalyst, Al2(SO4)3–H2SO4 complex, the structure of polymers was threo-di-isotactic. Though the configurations of all α-carbons were isotactic, a small amount of syndiotactic structure was observed in the β-carbon. On the other hand, in the amorphous polymer obtained from cis isomer by the homogeneous catalyst, the configuration of the α-carbon was isotactic, but that of the β-carbon was atactic. These facts suggest that the type of opening of a monomeric double bond is complicated, or that carbon–carbon double bond in an incoming monomer rotates in the transition state. From these experimental results, a probability treatment was proposed from the diad tacticity of α,β-disubstituted polymers. It shows that the tacticity is decided by a polymerization mechanism different from that proposed by Bovey.  相似文献   

8.
Depsipeptides and cyclodepsipeptides are analogues of the corresponding peptides in which one or more amide groups are replaced by ester functions. Reports of crystal structures of linear depsipeptides are rare. The crystal structures and conformational analyses of four depsipeptides with an alternating sequence of an α,α‐disubstituted α‐amino acid and an α‐hydroxy acid are reported. The molecules in the linear hexadepsipeptide amide in (S)‐Pms‐Acp‐(S)‐Pms‐Acp‐(S)‐Pms‐Acp‐NMe2 acetonitrile solvate, C47H58N4O9·C2H3N, ( 3b ), as well as in the related linear tetradepsipeptide amide (S)‐Pms‐Aib‐(S)‐Pms‐Aib‐NMe2, C28H37N3O6, ( 5a ), the diastereoisomeric mixture (S,R)‐Pms‐Acp‐(R,S)‐Pms‐Acp‐NMe2/(R,S)‐Pms‐Acp‐(R,S)‐Pms‐Acp‐NMe2 (1:1), C32H41N3O6, ( 5b ), and (R,S)‐Mns‐Acp‐(S,R)‐Mns‐Acp‐NMe2, C30H37N3O6, ( 5c ) (Pms is phenyllactic acid, Acp is 1‐aminocyclopentanecarboxylic acid and Mns is mandelic acid), generally adopt a β‐turn conformation in the solid state, which is stabilized by intramolecular N—H…O hydrogen bonds. Whereas β‐turns of type I (or I′) are formed in the cases of ( 3b ), ( 5a ) and ( 5b ), which contain phenyllactic acid, the torsion angles for ( 5c ), which incorporates mandelic acid, indicate a β‐turn in between type I and type III. Intermolecular N—H…O and O—H…O hydrogen bonds link the molecules of ( 3a ) and ( 5b ) into extended chains, and those of ( 5a ) and ( 5c ) into two‐dimensional networks.  相似文献   

9.
Ethylene polymerization reactions with many Ziegler–Natta catalysts exhibit several features which differentiate them from polymerization reactions of α-olefins: a relatively low ethylene reactivity, higher polymerization rates in the presence of α-olefins, a high reaction order with respect to ethylene concentration, and strong reversible rate depression in the presence of hydrogen. A detailed kinetic analysis of ethylene polymerization reactions (see ref. 1 ) provided the basis for a new reaction scheme which explains all these features by postulating the equilibrium formation of a Ti C2H5 species with the H atom in the methyl group β-agostically coordinated to the Ti atom in an active center. This mechanism predicts that the β-agostically stabilized Ti C2H5 groups can decompose in the β-hydride elimination reaction with expulsion of ethylene and the formation of a Ti H bond even in the absence of hydrogen in the reaction medium. If D2 is used as a chain transfer agent instead of H2, the mechanism predicts the formation of deuterated ethylene molecules, which copolymerize with protioethylene. To prove this prediction, several ethylene homopolymerization reactions were carried out with a supported Ziegler–Natta titanium-based catalyst in the presence of large amounts of D2. Analysis of gaseous reaction products and polymers confirmed the formation of several types of deuterated ethylene molecules and protio/deuterioethylene copolymers, respectively. In contrast, a metallocene catalyst, Cp2ZrCl2 MAO, does not exhibit these kinetic features. In the presence of deuterium, it produces only DCH2 CH2 (CH2 CH2)x CH2 CH2D molecules. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4273–4280, 1999  相似文献   

10.
The structure of ionic complex [Cp2Ti(L -Met)2]2+[Cl]2 (where Cp = η5-C5H5) possessing C2 symmetry is presented. Discrete cationic units with distorted tetrahedral geometry around the central titanium atom are connected through intermolecular H···Cl bonds between ammonium group protons of α-amino acid ligands and chloride anions. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

11.
In the title compounds, C21H30O4, (I), and C23H34O4, (II), respectively, which are valuable intermediates in the synthesis of important steroid derivatives, rings A and B are cis‐(5β,10β)‐fused. The two molecules have similar conformations of rings A, B and C. The presence of the 5β,6β‐epoxide group induces a significant twist of the steroid nucleus and a strong flattening of the B ring. The different C17 substituents result in different conformations for ring D. Cohesion of the molecular packing is achieved in both compounds only by weak intermolecular interactions. The geometries of the molecules in the crystalline environment are compared with those of the free molecules as given by ab initio Roothan Hartree–Fock calculations. We show in this work that quantum mechanical ab initio methods reproduce well the details of the conformation of these molecules, including a large twist of the steroid nucleus. The calculated twist values are comparable, but are larger than the observed values, indicating a possible small effect of the crystal packing on the twist angles.  相似文献   

12.
Hydrogen Bondings in α-KZnBr3 · 2 H2O The positions of the hydrogen atoms and the system of hydrogen bondings in the crystal structure of α-KZnBr3 · 2 H2O are discussed. The hydrogen atoms have been located by FOURIER difference synthesis. IR-spectra have given some information about the strength of the various hydrogen bondings O? H …? H and O? H …? Br.  相似文献   

13.
Dicyano-cobalt(III) complex acids of the type H[Co(α-Diox · H)2(CN)2] were obtained by air oxidation of an alcoholic aqueous solution of cobalt(II) acetate in the presence of α-dioxime (dimethylglyoxime. 1,2-cyclohexanedione dioxime or 1.2-cyclopentanedione dioxime) and KCN. From the solutions of the resulting K[Co(DH)2(CN)2], K[Co(Niox · H)2(CN)2] and K[Co(Cpdox · H)2(CN)2] the complex acids and 51 new salts were separated by means of double decomposition reactions. (DH = C4H7N2O2, Niox · H = C8H9N2O2 and Cpdox · H = C5H7N2O2.) New position and coordination isomeric compounds are described. From spectroscopical investigations in the UV and IR regions some structural problemes are discussed.  相似文献   

14.
Comparison of the structures of strychninium N‐phthaloyl‐β‐alaninate N‐phthaloyl‐β‐alanine, C21H23N2O2+·C11H8NO4·C11H9NO4, and brucinium N‐phthaloyl‐β‐alaninate 5.67‐hydrate, C23H27N2O4+·C11H8NO4·5.67H2O, reveals that, unlike strychninium cations, brucinium cations display a tendency to produce stacking inter­actions with cocrystallizing guests.  相似文献   

15.
In the title compounds, C18H20N2O2, (I), and C14H11N3O4·0.5H2O, (II), respectively, the oxime groups have an E configuration. In (I), the mol­ecules exist as polymers bound by intermolecular C—H⋯O and O—H⋯N hydrogen bonds around inversion centres. In (II), intermolecular OW—H⋯N, OW—H⋯O and O—H⋯OW interactions stabilize the molecular packing.  相似文献   

16.
Both 6‐(1H‐indol‐3‐yl)‐3‐methyl‐4‐(4‐methylphenyl)‐1‐phenyl‐1H‐pyrazolo[3,4‐b]pyridine‐5‐carbonitrile and 6‐(1H‐indol‐3‐yl)‐3‐methyl‐4‐(4‐methoxyphenyl)‐1‐phenyl‐1H‐pyrazolo[3,4‐b]pyridine‐5‐carbonitrile crystallize from dimethylformamide solutions as stoichiometric 1:1 solvates, viz. C29H21N5·C3H7NO, (I), and C29H21N5O·C3H7NO, (II), respectively; however, 6‐(1H‐indol‐3‐yl)‐3‐methyl‐1‐phenyl‐4‐(3,4,5‐trimethoxyphenyl)‐1H‐pyrazolo[3,4‐b]pyridine‐5‐carbonitrile, C31H25N5O3, (III), crystallizes in the unsolvated form. The heterocyclic components of (I) are linked by C—H...π(arene) hydrogen bonds to form cyclic centrosymmetric dimers, from which the solvent molecules are pendent, linked by N—H...O hydrogen bonds. In (II), the heterocyclic components are linked by a combination of C—H...N and C—H...π(arene) hydrogen bonds into chains containing two types of centrosymmetric ring, and the pendent solvent molecules are linked to these chains by N—H...O hydrogen bonds. Molecules of (III) are linked into simple C(12) chains by an N—H...O hydrogen bond, and these chains are weakly linked into pairs by an aromatic π–π stacking interaction.  相似文献   

17.
In the title compound, C31H40N2O·H2O, the outer two six‐membered rings are in chair conformations, while the central ring is in an 8β,9α‐half‐chair conformation. The five‐membered ring adopts a 13β‐envelope conformation and the cyano­benzyl­idene moiety has an E configuration with respect to the hydroxyl group at position 17. The steroid nuclei are linked by intermolecular O—H?O and O—H?N hydrogen bonds to form a molecular network. The molecular packing has an interesting feature, with the steroids aligned parallel to the b axis, forming a closed loop through hydrogen bonds linked via water mol­ecules.  相似文献   

18.
The title 3‐nitrophthalate–calcium coordination polymer, {[Ca(C8H3NO6)(H2O)2]·H2O}n, crystallizes as a one‐dimensional framework. The CaII centre has a distorted pentagonal–bipyramidal geometry, being seven‐coordinated by five O atoms from three different 3‐nitrophthalate groups and by two water molecules, resulting in a one‐dimensional zigzag chain along the a‐axis direction by the interconnection of the four O atoms from the two carboxylate groups. There is a D3 water cluster composed of the coordinated and the solvent water molecules within such chains. Adjacent chains are aggregated into two‐dimensional layers via hydrogen bonds in the c‐axis direction. The whole three‐dimensional structure is further stabilized by weak O—H...O hydrogen bonds between the O atoms of the nitro group and the water molecules.  相似文献   

19.
Contribution to the mass spectrometry of substituted α,ω-alkane diamines The main mass spectral fragmentation pattern of compounds of types 1 to 4 is discussed. After loss of C6H5 · CH2 · from the molecular ion the acid correspondin to the N,N-disubstituted residue is splitted off. The mechanism of this fragmentation reaction depends on the member of CH2-groups between the two nitrogen atoms (Schemes 1 and 3) and on the substitution pattern of both nitrogens (Scheme 2).  相似文献   

20.
Diphenyl(3‐methyl‐2‐indolyl)phosphine (C9H8NPPh2, 1 ) gives stable dimeric palladium(II) complexes that contain the phosphine in P,N‐bridging coordination mode. On treating 1 with [Pd(O2CCH3)2], the new complexes [Pd(μ‐C9H7NPPh2)(NCCH3)]2 ( 2 ) or [Pd(μ‐C9H7NPPh2)(μ‐O2CCH3)]2 ( 3 ) were isolated, depending on the solvent used, acetonitrile or toluene, respectively. Further reaction of 3 with the ammonium salt of 1 led to the substitution of one carboxylate ligand to afford [Pd(μ‐C9H7NPPh2)3(μ‐O2CCH3)] ( 4 ), in which the bimetallic unit is bonded by three C9H7NPPh2? moieties and one carboxylate group. Using this methodology, [Pd2(μ‐C6H4PPh2)2(μ‐C9H7NPPh2)(μ‐O2CCX3)] (X=H ( 7 ); X=F ( 8 )) were synthesised from the ortho‐metalated compounds [Pd(C6H4PPh2)(μ‐O2CCX3)]2 (X=H ( 5 ); X=F ( 6 )). Complexes 3 , 4 , 7 , and 8 have been found to be active in the catalytic β‐boration of α,β‐unsaturated esters and ketones under mild reaction conditions. Hindrance of the carbonyl moiety has an influence on the reaction rate, but quantitative conversion was achieved in many cases. More remarkably, when aryl bromides were added to the reaction media, complex 7 induced a highly successful consecutive β‐boration/cross‐coupling reaction with dimethyl acrylamide as the substrate (99 % conversion, 89 % isolated yield).  相似文献   

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