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1.
5-Alkyl-2-methyl-2-carbomethoxy-1,3-dioxanes were found to have a cis preferential configuration in the equilibrium state, and the ester hydrolysis rate of the trans-isomers was faster than that of the cis-isomers. Conformational analysis and charge calculation of the carbomethoxy group in both dioxanes elucidated this selectivity. 相似文献
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T.Bruce Grindley 《Tetrahedron letters》1982,23(17):1757-1760
The conformations of methyl, ethyl and isopropyl formate were shown to be present in equilibrium in a polar solvent with the conformations to significant (> 1% 230 K) but much lower extents than for t-butyl formate; rotational barriers for the former compounds are greaters. 相似文献
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O. V. Shishkin A. S. Polyakova S. N. Desenko D. V. Orlov S. V. Lindeman Yu. T. Struchkov 《Russian Chemical Bulletin》1995,44(3):470-474
The equilibrium geometry and inversion barriers of 5,6-dihydropyrimidine, 6,7-dihydroazolopyrimidines with node nitrogen atoms and their alkyl (Me, Et, Pri, But) and phenyl derivatives were calculated using a molecular mechanics approach. Annelation with azole cycles and the introduction of substituents have a slight effect on the equilibrium conformation of the dihydrocycle (distorted sofa). Alkyl substutuents at saturated carbons have an essentially equatorial orientation in 5,6-dihydropyridimine derivatives and are axial in the annelated analogs. On the other hand, the equatorial conformers are more stable in phenyl derivatives of dihydroazolopyrimidines. Factors determining the relative stability of conformers were analyzed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 487–491, March, 1995. 相似文献
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V. V. Kuznetsov 《Russian Journal of General Chemistry》2010,80(12):2491-2494
Computer simulation of the routes of conformational isomerization of 1,3,2-dioxathiane and its Soxides by nonempirical quantum-chemical method RHF/6-31G(d) revealed the main and local minima and transition states of this
process. It was shown that the barrier of ring inversion is reduced in going from 1,3,2-dioxathiane to its oxides. The established
ΔG
0 (300 K) value of S=O group in cyclic sulfite (−15.0 kJ mol−1) is in good agreement with the experimental data. 相似文献
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Force field calculations have been extended to include carboxylic acids and esters. Necessary parameters were chosen mainly by fitting to available experimental data on small molecules. A few key facts are not known experimentally, and these were found by carrying out ab initio (STO-3G) calculations. Other molecules were then studied and structural predictions were made. It is predicted that in isobutyric acid a methyl group is twisted 15° from eclipsing the carbonyl oxygen in the ground state. The relative energies and torsional functions for cyclohexanecarboxylic acid are reported. Except for rather simple compounds, such as normal chains, the carboxyl is usually twisted with respect to the attached chain. Some conformations of lactones were also examined. For δ-valerolactone it is predicted that the boat conformation is more stable than the chair. Heats of formation of the compounds can be calculated with fair accuracy. 相似文献
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Shishkin O. V. Polyakova A. S. Desenko S. M. Orlov V. D. Lindeman S. V. Struchkov Yu. T. 《Russian Chemical Bulletin》1994,43(6):944-947
The geometry of dihydropyridine and its alkyl derivatives was studied by the molecular mechanics method. The dihydrocycle was found to be mobile; however, substituents exert little effect on its distorted sofa conformation. The alkyl groups attached to the saturated carbon atoms occupy pseudo-equatorial position in monosubstituted and pseudo-axial positions in disubstituted 3,4-dihydropyridines. Unusually high barriers to inversion of the dihydrocycle were observed incis-3,4-dialkyl-3,4-dihydropyridines caused by the eclipse of the substituents in the transition state.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1009–1012, June, 1994. 相似文献
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G.A. Crowder 《Journal of fluorine chemistry》1973,3(2):133-140
Infrared spectra obtained for seven alkyl esters of heptafluorobutyric acid show that 18 vibrations of the CF3CF2CF2CO2 group have characteristic frequencies in these esters, with most having average deviations of only about 1 cm?1. The relative intensities of the bands are also quite constant. The infrared spectrum obtained for heptafluorobutyric acid indicates that the acid is completely associated in the neat liquid. 相似文献
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V. Ya. Kauss A. F. Mishnev I. Ya. Kalvin'sh 《Chemistry of Heterocyclic Compounds》1992,28(12):1439-1444
The betaines 2-amino-4,4-dimethyl-2-1,3,4-thiadiazolin-4-io-5-acetates are formed in the reaction of 1,1-dimethylthiosemicarbazides with propiolic acid. 2-Amino-4,4-disubstituted-5-carboalkoxy-methyl-2-1,3,4-thiadiazolinium chlorides, the structure of which has been confirmed by X-ray crystallography, are formed by the reaction of 1,1-disubstituted thiosemicarbazides lower alkyl propiolates in the presence of hydrochloric acid.Translated from Khimiya Geterotsiklicheskikh Soedenenii, No. 12, pp. 1674–1679, 1992. 相似文献
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Xiao Zhong Fu Sai Hong Jiang Jian Xin Yu She Yang RU Yun Ji 《中国化学快报》2007,18(7):817-819
A series of novel L-amino acid esters prodrugs of acyclic nucleoside phosphonates was synthesized and their anti-HBVactivity was evaluated in HepG2 2.2.15 cells. Compound 1d exhibited more potent anti-HBV activity and lower cytotoxicity than those of adefovir dipivoxil with EC50 and CC50 values of 0.207 mmol/L and 2530 mmol/L, respectively. 相似文献
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M. A. Allakhverdiev V. M. Farzaliev T. M. Khoiskaya N. Yu. Ibragimov E. M. Cherkasova 《Chemistry of Heterocyclic Compounds》1984,20(3):261-263
The reaction of amino thiols with chloroacetic acid esters leads to the formation of amino mercapto esters, whereas 6-alkyl(alkoxy)-N-aryltetrahydro-1,4-thiazine-3-ones are formed in the reaction with chloroacetic acid.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 327–329, March, 1984. 相似文献
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Two novel X-ray structures of the sulfonic ester derivatives 2-(6-iodo-1,3-benzodioxol-5-yl)ethyl 4-nitrobenzenesulfonate, 3, and 2-(6-iodo-1,3-benzodioxol-5-yl)ethyl 4-methylbenzenesulfonate, 4, have been obtained in a study aimed at analyzing the structures and conformations of sulfonic ester derivatives that are routinely used in alkaloid syntheses. The crystal structure of 4 is highly unusual, containing four independent molecules that belong to two distinct conformational types: (1) a hairpin conformation (stabilized mainly by intramolecular pi-stacking) and (2) a stepped conformation (stabilized mainly by intermolecular pi-stacking). Compound 3, on the other hand, crystallizes exclusively as the hairpin conformer. New MM+ force field parameters for sulfonic esters have been developed using the X-ray data, empirical rules, and DFT calculations to estimate the bond dipole parameters. Grid searches of conformational space for 3 and 4 using MM methods show that there are several gas-phase conformations within 5 kcal/mol of the global minimum and that the lowest energy conformations (by approximately 4.6 kcal/mol) are of the hairpin type. Analysis of the MM conformational energies suggests that the dominant intramolecular interaction stabilizing the hairpin conformations of 3 and 4 is van der Waals attraction. Moreover, the lattice energies for packing the hairpin conformations of 3 and 4 are approximately 4 kcal/mol more favorable than for the stepped conformations. Various intermolecular interactions contribute to the complexity of the observed crystal structures of 3 and 4, including electrostatic attraction between O and I atoms in neighboring molecules. Langevin dynamics (LD) simulations at several temperatures (6.0 ns, friction coefficient = 2.5 ps(-1)) indicate that the conformational exchange rates are approximately 10(10)-10(11) s(-1) over the temperature range 213-400 K, accounting for the temperature-independent (1)H NMR spectra of 3 and 4. 相似文献
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The syntheses and ambient-temperature 19F NMR data are reported for 27 asymmetric ethanes of the general formula RCF2CXYZ, including a complete series of 10 compounds with R = Cl and all combinations of the 5 ligands H, F, Cl, Br and Ph. Within the theoretical framework of a previously proposed heuristic mathematical model the geminal 19F chemical shift differences are fitted to chirality functions X = ?R (λx - λy) (λy - λz) (λz - λx) to yield acyclic conformational ligand constants λ and substituent parameters ?. It is demonstrated that the λ constants already reported for an analogous series of 10 compounds with R = Br are transferable to the Cl series with ?Cl = 0.63 ± 0.07. Crude first approximations are also reported for the normalised (according to ?Br = 1) ligand constants λCh3, λOH, λOCH3 and λ1 and for the substituent parameter λH. It is argued that the λ values thus ext play a role in the conformational analysis of asymmetric ethanes that is conceptually analogous to the conformational free energies in monosubstituted cyclohexanes. 相似文献
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P. N. Kondrat'ev Z. É. Skryabina V. I. Saloutin M. N. Rudaya T. A. Sinitsyna K. I. Pashkevich 《Russian Chemical Bulletin》1990,39(6):1273-1277
Esters of fluorinated acylpyruvic acids were obtained for the first time. PMR and IR spectroscopy, dipole moment measurements, and quantum chemical calculations showed that these compounds exist as equilibrium mixtures of E and Z enolic isomers.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1410–1414, June, 1990. 相似文献