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1.
The partial methylation of methyl β-glucoheptopyranoside has given a complex mixture of methyl ethers, from which five monomethyl ethers have been isolated by preparative GLC. Methylation of the latter gave a mixture in which ten dimethyl ethers were detected. The retention indices on the phase NPGS of the mono- and dimethyl ethers of methyl β-glucoheptopyranoside have been measured, and their mass spectra have been recorded and discussed. The mass spectra of these position isomers unambiguously characterize the pattern of methylation.  相似文献   

2.
Nine tri- and five tetramethyl ethers have been obtained by the partial methylation of methyl α- and β-glucoheptopyranosides and methyl 2,3,4,6,7-penta-O-acetyl1-α- and-β-glucoheptopyranosides. The retention indices of both types of methyl ethers on the liquid phase NPGS have been measured and the main directions of the fragmentation of these compounds under electron impact have been determined. The laws of the mass spectra of the position isomers that have been found will permit their use in GLC-MS analysis for determining the structure of a polysaccharide by the methylation method.  相似文献   

3.
The cationic copolymerizations of geometrical isomers of 1,2-dimethoxy- and 1,2-diethoxyethylenes with vinyl isobutyl ether as a reference monomer have been carried out in methylene chloride at ?70° using boron trifluoride etherate as catalyst. The kinetics of the acid-catalyzed hydrolysis of these ethers has also been investigated in 80% aqueous dioxane, in order to compare the results with the polymerizabilities. It has been found that the cis ethers are ca. four times as reactive as their trans isomers in both reactions. On the other hand, it has been proved that a β-alkoxyl substitution reduces the hydrolysis reactivity of vinyl alkyl ethers by a factor of ca. 10?3 while it even enchances the cationic polymerizability. These contrasting results are interpretable from the nature of the transition states which are different for the two reactions.  相似文献   

4.
4'-(2,6,6-Trimethyl-2-cyclohexen-1-yl)-3'-buten-2'-ketoxime-N-O-alkyl ethers have been synthesized starting from alpha-ionone, separated into their E and Z isomers and characterized on the basis of (1)H-NMR and mass spectra.  相似文献   

5.
Aromatic bispropenyl ethers are a new class of highly reactive thermosetting monomers that have been prepared and characterized. Two synthetic routes to their preparation have been developed. The first of these involves the base-catalyzed isomerization of bisallyl ether precursors that gives predominantly the Z bispropenyl ether isomers. The second method employs tris(triphenylphosphine)ruthenium(II) dichloride as an isomerization catalyst and produces predominantly the E isomers. Using these methods, a number of bispropenyl ether monomers containing different aromatic groups have been synthesized. The cationic polymerization of these novel monomers to give crosslinked network polymers using diaryliodonium salts as photo and thermal initiators has been studied.  相似文献   

6.
The relative thermodynamic stabilities of four isomeric vinyl ethers obtained by acid-catalyzed cleavage of MeOH from the dimethyl acetals of both 2-acetyltetrahydrofuran and 2-isobutyryltetrahydrofuran have been determined by chemical equilibration in cyclohexane solution. In addition, the structures and relative energies of many of these compounds have also been studied theoretically by DFT calculations. In each series of compounds, the endocyclic isomers, 5-(1-methoxyethyl)-2,3-dihydrofuran and 5-(1-methoxy-2-methylpropyl)-2,3-dihydrofuran, respectively, show the highest thermodynamic stabilities. This is particularly prominent for the vinyl ethers derived from 2-isobutyryltetrahydrofuran in which the equilibrium mixture consists of 90% of the endocyclic isomer at room temperature. The geometrical (exocyclic) isomers of the latter series of compounds show unexpected relative thermodynamic stabilities, but on the basis of the geometry-optimized structures provided by the DFT calculations, a reasonable explanation can be found.  相似文献   

7.
Summary Two crown ethers, di(tert-butylbenzo)-propyl-15-crown-5 polysiloxane (PSO-DTB-15C5) and dibenzo-propyl-15-crown-5 polysiloxane (PSO-DB-15C5) have been synthesized and coated onto fused-silica capillary columns. The chromatographic characteristics, including column efficiency, polarity, phase transition temperature, operating temperature range and selectivity, were studied.Excellent selectivity was obtained for the separation of polar position isomers, especially phenol and dinitrotoluene isomers. The separation mechanism is discussed.  相似文献   

8.
Thermal decarboxylation of potassium salts of perfluorocarboxylic acids in the presence of 20 mole % of crown ethers takes place in 1 h at 180°C and gives internal perfluoroolefins in yields of up to 95%. The predominance in product mixtures of isomers whose double bond is adjacent to the trifluoromethyl group is associated with kinetic control of the reaction. The kinetic parameters of the process have been found and the relative activities of a series of crown ethers have been established. A scheme is advanced to show their influence on the reaction studied.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2259–2261, October, 1991.  相似文献   

9.
Efficient reaction of bis-indolyl podand with different aldehydes using Fe(HSO43 as catalyst to afford the corresponding new indolyl crown ethers is described.The structures of three distinct isomers have been optimized using HyperChem geometry optimizations.Also percentage of each isomer was obtained with 1H NMR spectroscopy.  相似文献   

10.
Meso and racemic isomers of 1,1′-bis(α-hydroxyalkyl)ferrocene derivatives, and trans and cis isomers of 7-oxa[3]ferrocenophanes have been isolated. The configurations of these isomers have been determined both by spectroscopy and from their reaction behavior. It has been found that the ring-closure and ring-opening interconversion reactions between 1,1′-bis(α-hydroxyalkyl)ferrocenes and 7-oxa[3]ferrocenophanes are stereospecific. PMR spectra of the diols and ethers have been examined at 100 MHz in CF3COOH, and the existence of α-[1′-(α-hydroxyalkyl)ferrocenyl]carbonium ions has been demonstrated in this acid. A mechanism for the various interconversion reactions is proposed on the basis of their stereospecific reactivity and from the PMR spectra of the carbonium ions.  相似文献   

11.
To elucidate the effect of the introduction of a methyl group in the β-position of a vinyl monomer, propenyl alkyl ethers were copolymerized with vinyl ethers having the same alkoxy group. Propenyl alkyl ethers with an unbranched alkoxy group (ethyl or n-butyl propenyl ether) were more reactive than the corresponding vinyl ethers. This behavior is quite different from that of β-methylstyrene derivatives. However, propenyl alkyl ethers with branched alkoxy groups at the α carbon atom (isopropyl or tert-butyl propenyl ether) were less reactive than the corresponding vinyl ethers. Also, cis- isomers were more reactive than the trans isomers, regardless of the kind of alkoxy group and the polarity of the solvent.  相似文献   

12.
In this paper, we present generating functions for counting constitutional isomers and stereo isomers of acyclic saturated compounds consisting of O, C and H for the first time, and obtain the numbers of constitutional isomers and stereo isomers of acyclic saturated hydroxyl ethers. The numerical results are tabulated.  相似文献   

13.
This study presents the self-ion/molecule reaction (SIMR) spectra of three xylene isomers, and proposes an approach to differentiating them based on observed differences in relative abundances of ions formed by SIMR in an internal source ion trap instrument. It also demonstrates the applicability of SIMR for isomer discrimination, which is better than electron ionization (EI) and dimethyl ether chemical ionization (DME CI) in an ion trap mass spectrometer (ITMS) since no CI reagent, metal ions or internal standards are required to perform SIMR. The merits of the new method for distinguishing isomers are that it is simple, rapid and economic. To date, methyne addition products ([M+13](+) ions) have been observed for several nitrogenated compounds including aza-crown ethers, aniline and dopamine from SIMR in the ITMS. The xylene isomers are, however, the first three non-nitrogenated compounds that have been shown to produce the methyne addition ions in SIMR.  相似文献   

14.
O-Alkylation of thiotetronic acids gives a mixture of 2- and 4-position enol ether products. Comparison of the physical data revealed that UV spectroscopy was the most reliable method of distinguishing between these related ethers. We have determined that 4-position ethers have a distinct absorption between 235-240 nm, while 2-position ethers have two absorbance peaks, one between 205-220 nm and the other between 305-310 nm. This report describes the synthesis and unambiguous characterization of 2- and 4-methoxy-3,5-dimethylthiotetronic acids. The UV absorption properties of several other pairs of thiotetronic acid ethers confirm that these differences are general features that provide a simple method for distinguishing between 2- and 4-substituted isomers.  相似文献   

15.
用不对称二苯并14-冠-4-双羟基冠醚的顺式异构体(Ⅰ、Ⅲ)和反式异构体(Ⅱ)分别与丙二酰氯、丁二酰氧和己二酰氯反应,合成了14种桥链冠醚,用IR、1H NMR、MS和元素分析确证了它们的结构。结果表明,顺式异构体与丁二酰氧和己二酰氧反应可生成1:1和2:2缩合物,而与丙二酰氯反应则只生成2:2缩合物;反式异构体与3种脂肪二酰氯反应都生成2:2缩合物。  相似文献   

16.
The infrared spectra of the cis and trans geometric isomers of methyl and ethyl propenyl ethers have been recorded in the liquid and vapour phase, in the region 4000-200 cm?1. Solid phase spectra have also been recorded for all but trans methyl propenyl ether. Evidence is given for the existence of two rotameric forms for both the trans compounds, in each case the more stable conformer being planar s-cis; but a single non-planar conformation is suggested for the two cis isomers. The enthalpy difference between the two rotameric forms in trans ethyl propenyl ether was found to be 4.6 ± 1.0 kJ mol?1 (1100 ± 250 cal mol?1).  相似文献   

17.
E. Taskinen 《Tetrahedron》1978,34(4):433-436
13C NMR spectra of 5- and 6-membered heterocyclic vinyl ethers containing an endocyclic or exocyclic CC bond have been determined and the chemical shift of the β carbon of the vinyl group has been used as a measure of the extent of p-π conjugation in the vinyloxy system. The results show that in the 6-membered heterocyclic vinyl ethers with an exocyclic double bond, such as 2-methylenetetrahydropyran, p-π conjugation is essentially weaker than in the corresponding 5-membered heterocycles, such as 2- methylenetetrahydrofuran. In the respective endocyclic isomers, the difference in the extent of conjugation is considerably smaller, although the same relative order still applies. The spatial structures of these compounds are discussed on the basis of these findings.  相似文献   

18.
Fused silica capillary columns coated with several alkyl or acyl cyclodextrin derivatives, especially those of α- and β-cyclodextrins, are suitable for the enantiomer separation of a wide variety of volatile compounds of different molecular size and functionality. Positional isomers and more than 250 pairs of optical isomers have been resolved, including chiral hydrocarbons, acetals, ethers, epoxides, carbonates, lactones, esters, acids, ketones, aldehydes, alcohols, halocarbons, and also nitrogen-and sulfur-containing compounds. The physical properties of the cyclodextrin derivatives, even those obtained as viscous fluids, could be improved by dissolving them in polysiloxane liquid phases commonly used for GLC.  相似文献   

19.
Several v-triazoles were synthesized by 1,3-dipolar cycloaddition of certain α-azido ethers and α-azidothioethers to phenylacetylene. In most of the cases the reaction led to the formation of the two isomeric v-triazoles. Structural assignments for the products obtained were made on the basis of NMR data and chemical reactions. Characteristic differences between the NMR spectra of the isomers have been noted.  相似文献   

20.
All four stereoisomers of p-tert-butylsulfinylcalix[4]arene [4(rccc), 4(rcct), 4(rctt), and 4(rtct)], arising from the disposition of the four sulfinyl groups with respect to the mean plane of the four bridging sulfur atoms, have been prepared via oxidation of p-tert-butylthiacalix[4]arene (2) or its tetra-O-benzyl ethers 5 of defined conformations. Thus, treatment of 2 with 4.4 molar equiv of NaBO(3).4H(2)O gave the rtct and rctt isomers in 27% and 17% yields, respectively, while oxidation of cone 5 (5(C)) and partial cone 5 (5(PC)) proceeded stereoselectively to give, after debenzylation of the resulting tetrasulfoxides 12 and 15, the rccc and rcct isomers in 56% and 28% yields, respectively, based on 5. The sulfinylcalix[4]arenes 4 were treated with iodomethane in the presence of a base to give the corresponding tetramethyl ethers 16, the structures of which in regard to the disposition of the sulfinyl groups and the conformation of the phenol units were determined by X-ray crystallography. Also reported is the synthesis of all four conformational isomers of tetra-O-benzyl ether of 2 (5(C), 5(PC), 5(1,2-A), and 5(1,3-A)).  相似文献   

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