Controlling Glycosyl Bond Conformation of Guanine Nucleosides: Stabilization of the anti Conformer in 5′-O-Ethylguanosine

2012 ◽  
Vol 3 (5) ◽  
pp. 571-575 ◽  
Author(s):  
Hiroya Asami ◽  
Shu-hei Urashima ◽  
Masaki Tsukamoto ◽  
Ayaka Motoda ◽  
Yoshihiro Hayakawa ◽  
...  
Keyword(s):  
Anti Conformer

Synthesis and Characterization of Cl2HSi-O-NMe2

2004 ◽  
Vol 59 (11-12) ◽  
pp. 1505-1511 ◽  
Author(s):  
Krunoslav Vojinović ◽  
Norbert W. Mitzel ◽  
Thomas Foerster ◽  
W. H. Rankin
Keyword(s):  
Gas Phase ◽  
Reasonable Agreement ◽  
Synthesis And Characterization ◽  
Gauche Conformer ◽  
Anti Conformer ◽  
Donor And Acceptor ◽  
Multinuclear Nmr Spectroscopy ◽  
Repulsive Forces ◽  
Gas Phase Electron Diffraction

O-(Dichlorosilyl)-N,N-dimethylhydroxylamine, Cl2HSiONMe2, was synthesised by the reaction of O-lithio-N,N-dimethylhydroxylamine with an excess of trichlorosilane. The compound was characterised by multinuclear NMR spectroscopy (1H, 13C, 15N, 29Si), gas-phase IR spectroscopy and mass spectrometry. The structure of Cl2HSiONMe2 was determined by gas-phase electron diffraction. It exists as two conformers in the vapour, named anti and gauche after the position of the SiH hydrogen atom relative to the SiON skeleton. The anti:gauche ratio in the vapour was determined to be 40:60. The anti conformer shows only a weak attractive interaction between the geminal donor and acceptor centres N and Si [angle Si-O-N 111.1(20)­°], whereas these interactions are stronger in the gauche conformer [angle Si-O-N 98.8(12)°]. Further structure-determining forces from weak hydrogen bridges of the Si-Cl ···H-C type and van der Waals repulsive forces are also discussed. The experimental results are in reasonable agreement with ab initio calculations at the MP2/6-311++G** level of theory.

Gas- and liquid-phase proton NMR study of the syn-anti conformer equilibrium of ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl and neopentyl nitrite

1986 ◽  
Vol 90 (18) ◽  
pp. 4353-4358 ◽  
Author(s):  
Claire B. Conboy ◽  
J. Paul Chauvel ◽  
Phillip O. Moreno ◽  
Nancy S. True ◽  
C. M. Ott
Keyword(s):  
Liquid Phase ◽  
Proton Nmr ◽  
Tert Butyl ◽  
Nmr Study ◽  
Anti Conformer

scholarly journals Synthesis and isomerism of hydrazones of 2-(5-thioxo-4,5-dihydro-1,3,4-thiadiazol-2-ylthio)acetohydrazide

2007 ◽  
Vol 5 (4) ◽  
pp. 996-1006 ◽  
Author(s):  
Zenonas Kuodis ◽  
Albertas Rutavičius ◽  
Algirdas Matijoška ◽  
Olegas Eicher-Lorka
Keyword(s):  
Hydrogen Bond ◽  
Nitrogen Atom ◽  
Hydroxy Group ◽  
Intramolecular Hydrogen Bond ◽  
1H Nmr ◽  
Nmr Spectra ◽  
1H Nmr Spectra ◽  
Imino Group ◽  
Anti Conformer ◽  
Intramolecular Hydrogen

AbstractNew hydrazones of 2-(5-thioxo-4,5-dihydro-1,3,4-thiadiazol-2-ylthio)acetohydrazide have been obtained and the percentages of anti/syn - conformers were determined. Based on the analyses of 1H NMR spectra, it was concluded that for hydrazones obtained from the 2- hydroxybenzaldehydes and 2’-hydroxycetophenones the ratio between the anti-and syn-conformers depends on the strength of intramolecular hydrogen bond (IMHB) between the nitrogen atom of the imino group and the proton of the 2-hydroxy group. It was shown that increase in IMHB strength results in stabilization of the anti-conformer in solution.

The electronic absorption spectra of some N-sulfinylanilines. A molecular orbital treatment

1997 ◽  
Vol 75 (7) ◽  
pp. 934-941 ◽  
Author(s):  
R. Abu-Eittah ◽  
H. Moustafa ◽  
A.M. Al-Omar
Keyword(s):  
Absorption Spectra ◽  
Molecular Orbital ◽  
Electron Acceptor ◽  
Electronic Absorption ◽  
Electronic Absorption Spectra ◽  
Basis Sets ◽  
Theoretical Treatment ◽  
Molecular Orbital Calculations ◽  
Strong Electron ◽  
Anti Conformer

The electronic absorption spectra of N-sulfinylaniline and some of its derivatives were investigated using different solvents. The spectral behavior of the molecules indicated their planarity and that the NSO group is a strong electron acceptor. All the observed bands correspond to delocalized π → π* transitions; n → π* transition were not observed as discrete bands. Ab initio molecular orbital calculations were performed using four different basis sets. The results showed that the NSO group is nonlinear, the molecules studied are planar, and the syn conformer is more stable than the anti conformer. Keywords: N-sulfinylanilines, spectra and theoretical treatment.

The Molecular Structures and Conformational Preferences of Bis(dimethylstibyl)-Sulfane and -Tellurane, E(SbMe2)2, E = S or Te, Me = CH3, by Density Functional Theory Calculations and Gas Electron Diffraction

1998 ◽  
Vol 53 (3) ◽  
pp. 381-385 ◽  
Author(s):  
Arne Haaland ◽  
Dimitry J. Shorokhov ◽  
Hans Vidar Volden ◽  
Hans Joachim Breunig ◽  
Michael Denker ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Electron Diffraction ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Equilibrium Structure ◽  
Molecular Structures ◽  
Electron Diffraction Data ◽  
Functional Theory ◽  
Anti Conformer ◽  
Equilibrium Structures

Density functional theory calculations on E(SbMe2)2, E = S or Te, Me = CH3, indicate that the equilibrium structures are syn-syn or near syn-syn conformers with overall C2v or C2 symmetry. The calculations further indicate the existence of syn-anti conformers about 4 kJ mol-1 (E = S) or 1 kJ m ol-1 (E = Te) above the equilibrium structure. G as electron diffraction data show that both conform ers are present in gaseous S(SbMe2)2, while the presence of the syn-anti conformer in gaseous Te(SbMe2)2 is uncertain. The Sb - S and Sb - Te bond distances are 241.4(4) and 278.1(3) pm, respectively, the valence angles of the synsyn conformers are <SbSSb = 9 8.7(5)° and <SbTeSb = 91(2)°.

Medium-sized cyclophanes. Part 53.1 Synthesis and conformational studies, and photoinduced cyclization of syn-[n.2]metacyclophanenes

2000 ◽  
Vol 78 (8) ◽  
pp. 1089-1099 ◽  
Author(s):  
Takehiko Yamato ◽  
Koji Fujita ◽  
Keigo Futatsuki ◽  
Hirohisa Tsuzuki
Keyword(s):  
Transition State ◽  
X Ray Diffraction ◽  
Aromatic Rings ◽  
Chair Form ◽  
Transannular Cyclization ◽  
H Nmr ◽  
Anti Conformer ◽  
Anti Conformation ◽  
Polycyclic Aromatic ◽  
Mcmurry Reaction

A series of [n.2]metacyclophanenes (3) and (6) were prepared in good yields by a McMurry cyclization of 1,n-bis(3-acetyl-4-methoxyphenyl)alkanes (2) and 1,3-bis(3-formyl-4-methoxyphenyl)propane (5), respectively. Compounds 3b, 3c exist in the syn-conformation due to the steric repulsion between the methyl groups at the ethano bridge and the methoxy groups at the aromatic rings while compound 6 prefers the anti-conformation typical of [3.2]metacyclophanes. The assignment of syn-conformations has been confirmed by 1H NMR analyses and X-ray diffraction studies. Photoinduced transannular cyclization of [n.2]metacyclophanenes (3) and (6) in the presence of iodine as an oxidant afforded phenanthrene-anellated polycyclic aromatic hydrocarbons. Apparently, the rate of the photocyclization of anti-6 was found to be much faster than that of syn-3b and almost completed within 1 h. Thus, the different reactivities for the irradiation of syn- and anti-conformer were observed. The reason for the present preference for the formation of trans-dihydrophenanthrene rather than cis-dihydrophenanthrene as the intermediate might be attributable to the more stable chair form transition state than boat one and the conformational fixation to the chair form in the ground and transition state is possible in the anti-conformer.Key words: cyclophanes, strained molecule, McMurry reaction, C—C coupling, conformation analysis, cyclizations, photolysis, transannular reactions, transition states.

scholarly journals The effect of substituents on the syn-anti conformer ratio in naphthyl-based imidazolinium salts and their corresponding N-heterocyclic carbenes

ARKIVOC ◽  
2010 ◽  
Vol 2011 (6) ◽  
pp. 176-198 ◽  
Author(s):  
Michele Gatti ◽  
Linglin Wu ◽  
Emma Drinkel ◽  
Fiona Gaggia ◽  
Sascha Blumentritt ◽  
...  
Keyword(s):  
Heterocyclic Carbenes ◽  
Effect Of Substituents ◽  
Anti Conformer ◽  
Imidazolinium Salts
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