Dimerization and solvent-assisted proton dislocation in the low-barrier hydrogen bond of a Mannich base: a low-temperature NMR study

2001 ◽  
Vol 39 (S1) ◽  
pp. S81-S90 ◽  
Author(s):  
Maria Rospenk ◽  
Lucjan Sobczyk ◽  
Parwin Schah-Mohammedi ◽  
Hans-Heinrich Limbach ◽  
Nicolai S. Golubev ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Low Temperature ◽  
Mannich Base ◽  
Nmr Study

scholarly journals 51V-NMR study of low-temperature phase in δ-Ag2/3V2O5

2015 ◽  
Vol 592 ◽  
pp. 012042 ◽  
Author(s):  
Y Kawasaki ◽  
R Morioka ◽  
Y Kishimoto ◽  
K Nakamura ◽  
K Nishiyama ◽  
...  
Keyword(s):  
Low Temperature ◽  
Temperature Phase ◽  
51V Nmr ◽  
Nmr Study ◽  
Low Temperature Phase

scholarly journals Hydrogen Bond Studies. 126. A 2H NMR Study of LiClO4.3D2O at 25 and -71 degrees C.

1978 ◽  
Vol 32a ◽  
pp. 1-5 ◽  
Author(s):  
Bo Berglund ◽  
Jörgen Tegenfeldt ◽  
Hilda Kvila ◽  
Arne F. Andresen ◽  
Olav Smidsrød ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
2H Nmr ◽  
Nmr Study

Conformational sampling of bioactive conformers: a low-temperature NMR study of15N-Leu–enkephalin

1998 ◽  
Vol 4 (4) ◽  
pp. 253-265 ◽  
Author(s):  
Pietro Amodeo ◽  
Fred Naider ◽  
Delia Picone ◽  
Teodorico Tancredi ◽  
Piero A. Temussi
Keyword(s):  
Low Temperature ◽  
Conformational Sampling ◽  
Nmr Study

Dynamisches Verhalten dimerer 1,3,2,4λ2-Diazasilastannetidine und -plumbetidine in Lösung — eine Multikern-NMR-Studie/Dynamic Behaviour of Dimeric 1,2,3,4λ2-Diazasilastannetidines and -plumbetidines in Solution — a Multinuclear NMR Study

1989 ◽  
Vol 44 (3) ◽  
pp. 288-292 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Klaus Horchler ◽  
Hong Zhou ◽  
Michael Veith
Keyword(s):  
Low Temperature ◽  
Dynamic Process ◽  
Room Temperature ◽  
Dynamic Behaviour ◽  
The Other ◽  
Multinuclear Nmr ◽  
Nmr Data ◽  
Nmr Study ◽  
Intramolecular Process

1,3-Diisopropyl-2,2-dimethyl-1,3,2,4λ2-diazasilastannetidine (1b) and -plumbetidine (2b) are dimeric [(1b)2, (2b)2] in solution. At room temperature the structure of (1b)2 is fluxional. The dynamic behaviour is interpreted - on the basis of 1H. 13C, 29Si and 119Sn NMR data - as an intramolecular process in which the four-membered rings keep their identity. Such a process involves either concerted opening of the two coordinative Sn - N bonds and mutual slippage of the two rings, or consecutive cleavage of one of the coordinative Sn - N bonds and rotation about the other one. At room temperature the dimer (2b)2 is in equilibrium with its monomer 2b, whereas at low temperature the dynamic process corresponds to that established for (1b)2. In solutions which contain a mixture of the dimers (1b)2 and (2b)2, the presence of the mixed dimer 1b/2b can be proved unambiguously by consistent 29Si, 119Sn and 207Pb NMR data.

Mécanisme de la réaction de glycosylation par réversion acide en présence d'anhydride trifluorométhane sulfonique comme agent de condensation

1981 ◽  
Vol 59 (2) ◽  
pp. 482-489 ◽  
Author(s):  
André A. Pavia ◽  
Sak N. Ung-Chhun
Keyword(s):  
Low Temperature ◽  
Necessary Conditions ◽  
Free Acid ◽  
Trifluoromethanesulfonic Acid ◽  
Nmr Study ◽  
Trifluoromethanesulfonic Anhydride ◽  
Glycosylation Reaction ◽  
Comme Agent ◽  
Mechanism Of The Reaction

The acid-catalysed mechanism of the reaction using trifluoromethanesulfonic anhydride to synthesize symmetrical 1,1′-glycosyl-glycosides such as trehalose and galacto, manno, arabino, xylo etc. analogues has been elucidated. The authors were able to prove by 19F nmr study at low temperature that the efficiency of the system is due to the peculiar property of trifluoromethanesulfonic acid generated in situ to form a stable, insoluble hydroxonium trifluoromethanesulfonate CF3SO3− H3O+. The procedure satisfies the two necessary conditions for a glycosylation reaction being workable: (i) the presence in catalytic amounts of free acid which is regenerated during the condensation step; (ii) a very efficient trapping of the water liberated during the protonation step which displaces the equilibrium towards the formation of the glycoside. The α-stereoselectivity of the reaction is discussed in terms of anomerisation of the β-anomers on to the thermodynamically more stable α ones, through a cyclic oxonium intermediate.

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