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1.
When α-halo sulfides are reacted with ambident 2-pyrimidinones, the major product is due to N-alkylation, the minor product to O-alkylation. N-Alkylation is favoured by the presence of a tertiary amine in a solvent of low dielectric constant and also by a change of the α-halo sulfide substituent from chlorine to iodine. Complete selectivity can be achieved. The course of the reaction is rationalized in terms of the HSAB-principle. 相似文献
2.
CD spectra of acyclic α-N,N-dimethylamino ketones exhibit two absorption bands of opposite sign at ca. 240 and 305–315 nm. Both bands are ascribed to the same conformers. On protonation only one CD band is seen. The single CD band of α-N,N,N-trimethylammonio ketones has the same sign and almost the same wavelength maximum as the protonated amino ketones. 相似文献
3.
Ionization potential measurements of the volatile species from the three isomers of the tautomeric hydroxyl and mercapto pyridines show that these are in the hydroxy and mercapto forms rather than appearing as lactams and betaines. The corresponding N-methyl lactams and S- and O-methyl ethers were also studied for comparative purposes. 相似文献
4.
The mass spectra of the three isomeric trimethylanilinium oxides and their methyl-d3 analogues show that the m- and p- isomers undergo intermolecular trans-O-alkylation before evaporation. In the o-isomer, only 10% transalkylated product is observed and there is strong evidence that most of this isomer evaporates without undergoing structural changes. By indirect introduction, however, the o-isomer showed only transalkylated product. The most important fragmentation patterns on electron-impact are α-cleavage on the N-methyl carbon or expulsion of the O-substituent with formation of a quinoid structure. The latter dominates for the o- and p-methyl ethers while the former is the most important pathway for the m-isomer and for the corresponding phenols. Lower fragments are of modest intensity. 相似文献
5.
o-N,N,N-Trimethylanilinium oxide is evaporated structurally unchanged, admixed with the corresponding transalkylated ether. The ionization potential for the anilinium oxide was determined as 6·8 eV which was 0·8 eV lower than for the corresponding ether. An explanation for the unusually low IP value is advanced. In IP measurements in binary mixtures the semi-log plot method showed parallel curves for different compositions in the gas phase, but no linear relationship between the recorded IP and composition was found. Appearance potential measurements show that the energy of the zwitterion in the gas phase is at least 10 kcal/mol higher than in the corresponding ether. 相似文献
6.
Ionization potentials of a number of substituted pyridines have been measured. The ionization potential is dependent on the substituent properties. Derivatives of pyridinium-3-oxide are unusual in that they have considerably lower IP values than isomeric covalent structures. 相似文献
7.
The crystal structures of 4,7-phenanthrolino-5,6:5,6-pyrazine tetrahydrate (I) and 1,4,5,8,9,12-hexaazatriphenylene dihydrate (II) have been determined from low temperature (173 K) x-ray single crystal diffraction data. I crystallizes in the triclinic system, space group P
with a = 11.2687(6), b = 12.4766(6), c = 12.7068(7) Å, = 113.4740(10), = 91.605(2), = 114.587(2)°, V = 1449.33(13) Å3, and Z = 4. II crystallizes in the orthorhombic system, space group Pca21 with a = 18.187(2), b = 9.2576(11), c = 6.9672(8) Å, V = 1173.0(2) Å3, and Z = 4. In both structures the planar heterocyclic molecules stack with interplanar distances down to 3.3 Å, which is consistent with self--complexation. The crystal water molecules provide links between the columns of stacked molecules through hydrogen bonds. In each compound the N-C bond lengths fall into two distinct groups (mean values 1.330(3) vs 1.361(1) Å in I and 1.320(3) vs 1.357(5) Å in II), as do the C-C bonds of the central phenyl rings (1.411(4) vs 1.467(1) Å in I and 1.405(5) vs 1.458(4) Å in II). 相似文献
8.
Nguyen S Alund SJ Hiorth M Kjøniksen AL Smistad G 《Colloids and surfaces. B, Biointerfaces》2011,88(2):664-673
The present study investigated the surface coating of charged liposomes by three different types of pectin (LM, HM and amidated pectin) by particle size determinations and zeta potential measurements. The pectins and the pectin coated liposomes were visualized by atomic force microscopy. The adsorption of pectin onto positive liposomes yielded a reproducible increase in particle size and a shift of the zeta potential from positive to negative side for all three pectin types, whereas the adsorption of pectin onto negative liposomes did not render any significant changes probably due to electrostatic repulsion. The positive liposomes coated with HM-pectin gave the largest pectin coated particles with the least negative zeta potential, while the opposite was observed for the LM-pectin coated positive liposomes. Furthermore, results from dynamic light scattering revealed narrow size distributions, indicating that the degree of aggregation was low for the pectin coated liposomes. As liposomes are able to encapsulate drugs and pectin has been found to be mucoadhesive, these pectin coated liposomes may be potential drug delivery systems. 相似文献
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10.
Carnitine and its O-acyl derivatives undergo two major pyrolytic reactions in the mass spectrometer. Firstly elimination of water from carnitine or acid from acylcarnitine takes place followed by intramolecular displacement and formation of crotonyl lactone and trimethylamine. Secondly intramolecular displacement occurs with formation of a substituted γ-lactone and trimethylamine. For the lower acid derivatives only the elimination pathway is important. For carnitine and higher derivatives both processes are important. The electron induced fragmentations of the major pyrolysis products are relatively simple. The most important pathways for the major components are discussed. The pyrolytic composition and mode of fragmentation are characteristic and can be used for identification purposes. 相似文献