Synthesis and conformational analysis of disaccharide analogues containing disulfide and selenosulfide functionalities in the interglycosidic linkages

2005 ◽  
Vol 83 (6-7) ◽  
pp. 929-936 ◽  
Author(s):  
Nagasree Chakka ◽  
Blair D Johnston ◽  
B Mario Pinto
Keyword(s):  
Nmr Spectra ◽  
Variable Temperature ◽  
Conformational Space ◽  
Molecular Orbital Theory ◽  
Line Broadening ◽  
Orbital Theory ◽  
Synthetic Strategy ◽  
Conformational Preferences ◽  
Variable Temperature Nmr Spectra ◽  
Low Energy Conformations

The synthesis of novel disaccharides containing disulfide (methyl-4-S-(β-D-galactopyranosyl-1'-thio)-4-thio-α-D-glucopyranoside (1)) and selenosulfide (methyl-4-Se-(β-D-galactopyranosyl-1'-thio)-4-seleno-α-D-glucopyranoside (2)) functionalities in the interglycosidic linkages is described. The synthetic strategy relied on the reaction of a β-glycosylthiosulfonate with a carbohydrate thiol or selenol nucleophile. The resulting protected β-dihetero-linked disaccharides were deprotected to give the target compounds. The conformational preferences of these dihetero analogues were inferred from NOESY experiments and line-broadening effects in variable-temperature NMR spectra, and are rationalized in terms of molecular orbital theory. Low-energy conformations of these compounds can populate regions of conformational space not usually occupied by β-linked disaccharides, and offer the possibility for presentation of novel ligand topographies.Key words: disaccharides, disulfides, selenosulfides, interglycosidic linkages, conformations, MO explanation.

X-ray Structure and Variable Temperature NMR Spectra of [meso-Triarylcorrolato]copper(III)

2003 ◽  
Vol 42 (15) ◽  
pp. 4495-4497 ◽  
Author(s):  
Christian Brückner ◽  
Raymond P. Briñas ◽  
Jeanette A. Krause Bauer
Keyword(s):  
Nmr Spectra ◽  
Variable Temperature ◽  
X Ray ◽  
Variable Temperature Nmr Spectra

Creation of a Simple Stable Enol. The Stabilizing Properties of the Diazonium Substituent

1979 ◽  
Vol 32 (7) ◽  
pp. 1401 ◽  
Author(s):  
MJ Ballard ◽  
WJ Bouma ◽  
L Radom ◽  
MA Vincent
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Electron Acceptor ◽  
Vinyl Alcohol ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Conformational Preferences ◽  
Alcohol System ◽  
Optimized Geometries

Ab initio molecular orbital theory is used to examine the effect of the diazonium substituent (N2+) on the keto-enol equilibrium in the acetaldehyde/vinyl alcohol system. The conformational preferences of the two isomers are examined, and optimized geometries obtained for the best conformers. The diazonium substituent is a strong π-electron acceptor and σ-electron acceptor, and accordingly destabilizes the keto isomer and stabilizes the enol isomer. The effect of the diazonium substituent is sufficiently large to make the enol isomer substantially lower in energy than the keto isomer.

Conformational preferences of the benzenedicarbaldehydes: an ab initio molecular-orbital, dipole-moment and Kerr-effect study

1984 ◽  
Vol 37 (3) ◽  
pp. 465 ◽  
Author(s):  
D Mirarchi ◽  
L Phillips ◽  
H Lumbroso ◽  
GLD Ritchie
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Kerr Effect ◽  
Dipole Moments ◽  
Effect Study ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Molecular Plane ◽  
Conformational Preferences ◽  
Kerr Constants

Ab initio molecular orbital theory at the STO-3G level is used to elucidate the structures and relative abundances of stable conformations of the three benzenedicarbaldehydes. In addition, new measurements of the infinite-dilution dipole moments and molar Kerr constants of these molecules as solutes in dioxan at 25�C are reported and analysed. The previously recognized inability of the simple group- additivity model to reliably predict the anisotropy in the polarizability of benzene-1,4-dicarbaldehyde is shown to be due to a redistribution of the polarizability in the molecular plane.

Keto-enol tautomerism. Relative stabilization of enol isomers

1978 ◽  
Vol 31 (6) ◽  
pp. 1167 ◽  
Author(s):  
WJ Bouma ◽  
L Radom
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Vinyl Alcohol ◽  
Energy Difference ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Conformational Preferences ◽  
Relative Stabilization ◽  
Alcohol System ◽  
Li Substitution

Ab initio molecular orbital theory is used to examine the effect of simple π-electron-accepting substituents (Li, BeH, BH2) on the keto-enol equilibrium in the acetaldehyde-vinyl alcohol system. The enol-keto energy difference is increased slightly by α-Li substitution and decreased to a near-zero value by a BH2 substituent. The results are rationalized in terms of geminal interactions. The conformational preferences of substituted acetaldehyde systems (XCH2CHO; X = Li, BeH, BH2, CH3, F) are discussed. Three classes of rotational potential functions are distinguished on the basis of the σ-electron-donating or -accepting nature of the substituent.

Conformational preferences of the fluoromethyl group in p-methylbenzyl fluoride and some derivatives

1980 ◽  
Vol 58 (12) ◽  
pp. 1178-1182 ◽  
Author(s):  
Ted Schaefer ◽  
Walter P. Niemczura ◽  
Rudy Sebastian ◽  
Leonard J. Kruczynski ◽  
Werner Danchura
Keyword(s):  
Benzene Ring ◽  
Molecular Orbital ◽  
Molecular Orbital Theory ◽  
Conformational Preference ◽  
Orbital Theory ◽  
Carbon Bond ◽  
Carbon Carbon Bond ◽  
Conformational Preferences ◽  
Good Agreement

The coupling over seven bonds between 19F nuclei and protons in p-methylbenzyl fluoride and a series of ring-substituted derivatives is used to estimate the value for a conformation in which the C—F bond lies in a plane perpendicular to the benzene ring. The J method is then used to show that in CS2 solution, the Conformational preference of the fluoromethyl group is very weak in 3,5-dichloro-4-methylbenzyl fluoride and in 3,5-dibromo-4-methylbenzyl fluoride. The barrier to rotation about the exocyclic carbon—carbon bond is perhaps as large as 0.2 kcal/mol. In p-methylbenzyl fluoride, the C—F bond prefers a plane perpendicular to the benzene plane by ca. 0.9 kcal/mol. Good agreement is found with the Conformational preferences based on couplings over six or seven bonds between the methylene protons and the para ring or methyl protons. The deductions are compared with calculations at various levels of molecular orbital theory.

An ab initio approach to creating a simple stable enol

1978 ◽  
Vol 31 (8) ◽  
pp. 1649 ◽  
Author(s):  
WJ Bouma ◽  
L Radom
Keyword(s):  
Potential Energy ◽  
Ab Initio ◽  
Energy Difference ◽  
Electron Acceptors ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Keto Form ◽  
Conformational Preferences ◽  
Alcohol System ◽  
Ab Initio Approach

Ab initio molecular orbital theory is used to examine the effect of four substituents (CN, NO2, NO and CHO) which are π-electron acceptors and σ-electron acceptors on the keto-enol equilibrium in the acetaldehyde/vinyl alcohol system. Each substituent destabilizes the keto isomer and stabilizes the enol isomer as desired and hence decreases the enol-keto energy difference. For the NO and CHO substituents, the effect is sufficiently large that the enol isomer is predicted to be slightly lower in energy than the keto form. The conformational preferences of the keto isomers are discussed in detail and a conformational potential energy map is presented for malondialdehyde.

The internal rotational potential in benzyl chloride

1986 ◽  
Vol 64 (7) ◽  
pp. 1322-1325
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Glenn H. Penner
Keyword(s):  
Internal Rotation ◽  
Long Range ◽  
Nmr Spectra ◽  
Benzyl Chloride ◽  
Polar Solvent ◽  
Low Energy ◽  
Coupling Constants ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
H Nmr

The 1H nmr spectra of benzyl chloride in dilute CS2 and acetone-d6 solutions are analyzed. The long-range coupling constants are consistent only with a low-energy conformation in which the C—Cl bond lies in a plane perpendicular to the benzene plane. Geometry optimized computations at the STO 3G level of molecular orbital theory agree with this conclusion and yield a nearly pure twofold barrier to internal rotation of 8.6 kJ/mol. In CS2 solution the long-range couplings yield 8.8 kJ/mol, rising to 11.2 kJ/mol in acetone solution. This increase in the internal barrier in a polar solvent is similar to that found for benzyl fluoride, but in the latter the barrier itself is very much smaller than in benzyl chloride.

Siliciumverbindungen mit starken intramolekularen sterischen Wechselwirkungen, XIV [1] Versuche zur Synthese des Tetra-tert-butylsilans: Tri-tert-butylisopropylsilan und verwandte Verbindungen / Silicon Compounds with Strong Intramolecular Steric Interactions, XIV [1] Attempted Synthesis of Tetra-tert-butylsilane: Tri-tert-butylisopropylsilane and Related Compounds

1983 ◽  
Vol 38 (9) ◽  
pp. 1062-1068 ◽  
Author(s):  
Manfred Weidenbruch ◽  
Hermann Flott ◽  
Bernd Ralle ◽  
Karl Peters ◽  
Hans Georg von Schnering
Keyword(s):  
Nmr Spectra ◽  
Hydrogen Exchange ◽  
Variable Temperature ◽  
Silicon Compounds ◽  
X Ray ◽  
Tert Butyl ◽  
Step Procedure ◽  
Variable Temperature Nmr Spectra ◽  
Related Compounds

AbstractReaction of tri-tert-butyl(dihalomethyl)silanes (halo = chloro, bromo) with organolithium compounds, by lithium/halogen or lithium/hydrogen exchange, leads to the corresponding carbenoids which by lithium halide elimination could give the carbenes (t-C4H9)3SiCX. Further intermolecular or intramolecular reaction of these reactive intermediates provides a variety of crowded molecules including alkyltri-tert-butylsilanes, 1,2-bis(tri-tert-butylsilyl)- substituted ethanes and ethenes and ring substituted 1,2-di-tert-butyl-1-silacyclo-butanes. An X-ray structure determination of (E)-1,2-bis(tri-tert-butylsilyl)-1,2-dichloroethene reveals neither a twisting nor an elongation of the CC double bond, but the C = C-Si bond angles exhibit rather unusual values (up to 137.7°) and the Si-C (sp2) bonds are as long as 195 pm.Tri-tert-butylisopropylsilane was prepared by a two step procedure and characterized by its variable temperature NMR spectra. The attempted synthesis of tetra-tert-butylsilane by reactions of the compound with bromine followed by treatment with methyllithium afforded only tri-tert-butylisopropenylsilane.

Bonding in Transition Metal Silyl Dimers. Molecular Orbital Theory

1989 ◽  
Author(s):  
Alfred B. Anderson ◽  
Paul Shiller ◽  
Eugene A. Zarate ◽  
Claire A. Tessier-Youngs ◽  
Wiley J. Youngs
Keyword(s):  
Transition Metal ◽  
Molecular Orbital ◽  
Molecular Orbital Theory ◽  
Orbital Theory
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