Protonation of a conjugated Schiff base by weak to strong acids: a 13C and 15N nuclear magnetic resonance study

1987 ◽  
Vol 65 (3) ◽  
pp. 661-665 ◽  
Author(s):  
Daniel Cossette ◽  
Daniel Vocelle
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Schiff Base ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Nuclear Magnetic Resonance Study ◽  
Nonpolar Solvents ◽  
Polar Groups ◽  
Tert Butylamine ◽  
Strong Acids ◽  
Nuclear Magnetic

The interactions (mostly protonation) between several carboxylic and mineral acids and trans,trans-2,4-heptadienylidene tert-butylamine (HBA) were determined by 13C and 15N nuclear magnetic resonance spectroscopies. Results indicate that protonation is only partial with weak acids in both polar and nonpolar solvents. No interaction between polar groups located on the acids and the polyenic chain of HBA seems to occur. The chemical shifts of all carbon atoms and also of the Schiff base nitrogen are linearly correlated with the acidity strength of the carboxylic acids.

A 13C and 15N nuclear magnetic resonance study of the protonation of a retinal Schiff base by acids of different pKas and in solvents of different polarities

1987 ◽  
Vol 65 (7) ◽  
pp. 1576-1583 ◽  
Author(s):  
Daniel Cossette ◽  
Daniel Vocelle
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Schiff Base ◽  
Magnetic Resonance ◽  
Specific Interaction ◽  
Nuclear Magnetic Resonance Study ◽  
Polar Groups ◽  
Nuclear Magnetic Resonance Spectra ◽  
Mineral Acids ◽  
Tert Butylamine ◽  
Nuclear Magnetic

13C and 15N nuclear magnetic resonance spectra of mixtures of all-trans-retinylidene tert-butylamine (RtBA) and substituted acetic acids in equimolar concentrations in both CDCl3 and CD3OD were studied in relation to two questions: the nature of the state of protonation of a retinal Schiff base in the presence of carboxylic and mineral acids in solvents of different polarities, and secondly, to determine the nature of the interactions (if any) between the polar groups located on the acids and the polyenic chain of the retinal derivative. Using carboxylic acids of different pKas and three mineral acids, we present results that indicate that, in solvents of low polarity, weak acids can only partially protonate RtBA while, in a more polar milieu, the protonation percentages are higher. With polar groups such asNO2, Cl, Br, I, and CN, no specific interaction could be found between the polyenic chain of the imine and these groups. Variations in the intensity of certain peaks of RtBA were noted and these could possibly be related to the presence of the polar groups on the acids. Comparisons of our results with those obtained on rhodopsin and bacteriorhodopsin indicate that the milieu surrounding the chromophore must be polar if protonation is complete, while in a less polar environment partial protonation can be expected.

A carbon-13 CP/MAS nuclear magnetic resonance study of several 1,4-disubstituted benzenes in the solid state

1989 ◽  
Vol 67 (3) ◽  
pp. 525-534 ◽  
Author(s):  
Glenn H. Penner ◽  
Roderick E. Wasylishen
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Solid State ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Nuclear Magnetic Resonance Study ◽  
Solution Studies ◽  
Temperature Solution ◽  
Cp Mas Nmr ◽  
Nuclear Magnetic

The carbon-13 chemical shifts of several 1,4-disubstituted benzenes in the solid state are reported. At least one of the substituents is unsymmetrical and in most cases this leads to different 13C chemical shifts of C-2 and C-6 and in some cases to different shifts for C-3 and C-5. The 13C chemical shifts observed in the solid state are compared with those measured in solution and, where possible, with those obtained in low temperature solution studies where internal rotation of the unsymmetrical substituent is slow on the 13C chemical shift time scale. Agreement between the chemical shifts observed in the solid state and solution is excellent. The potential application of CP/MAS nuclear magnetic resonance in deducing the conformation of benzene derivatives with two unsymmetrical substituents is discussed. Keywords: carbon-13 CP/MAS NMR, 13C NMR chemical shifts, substituent effects.

Nuclear Magnetic Resonance Study of Caesium-133 in Binary Molten Trifluoroacetate Salt Mixtures

2001 ◽  
Vol 56 (3-4) ◽  
pp. 288-290 ◽  
Author(s):  
V. N. Mirny ◽  
V. V. Trachevski ◽  
T. A. Mimaya
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Chemical Shifts ◽  
Nuclear Magnetic Resonance Study ◽  
Magnetic Resonance Study ◽  
Sodium Potassium ◽  
Salt Mixtures ◽  
Nuclear Magnetic

Abstract The chemical shifts of Cs+ in binary melts of caesium trifluoroacetate with lithium, sodium, potassium or thallium trifluoroacetates have been studied as a function of composition. An influence of added foreign cations on chemical shift of caesium nuclei has been found. The nature of the intra-and intermolecular paramagnetic contributions into the shifts of 133Cs is discussed.

A 1H and 13C nuclear magnetic resonance study of nucleosides with methylated pyrimidine bases

1982 ◽  
Vol 60 (24) ◽  
pp. 3026-3032 ◽  
Author(s):  
Frank E. Hruska ◽  
Wayne J. P. Blonski
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Nuclear Magnetic Resonance Study ◽  
Coupling Constants ◽  
Magnetic Resonance Data ◽  
Proton Coupling ◽  
13C Nuclear Magnetic Resonance ◽  
Pyrimidine Bases ◽  
Nuclear Magnetic

Alkylated pyrimidine bases are of interest from the viewpoint of mutagenesis and carcinogenesis. 1H nuclear magnetic resonance data are presented for a series of ribosides and arabinosides alkylated at the O2,O4, N3, and C5 positions of the pyrimidine base. The data provide information about the stereochemical effects of base methylation. The J(5—6) proton coupling constants show that O-alkylation leads to a decrease in the π-bond order of the C5—C6 bond. The 13C chemical shifts are related to the tautomeric changes effected by O-alkylation.

A nitrogen-15 nuclear magnetic resonance study of N-aryl phosphoramidates and phosphorimidates

1980 ◽  
Vol 58 (23) ◽  
pp. 2442-2446 ◽  
Author(s):  
G. W. Buchanan ◽  
F. G. Morin ◽  
R. R. Fraser
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Aromatic Ring ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Nuclear Magnetic Resonance Study ◽  
Magnetic Resonance Study ◽  
Nuclear Magnetic

15N nuclear magnetic resonance chemical shifts and one-bond 15N—31P couplings are reported for a series of five N-arylphosphoramidates and four N-arylphosphorimidates. Results are interpreted in terms of an extensively delocalized N lone pair in the phosphoramidates, with pπ–pπ donation into the aromatic ring being dominant over pπ–dπ donation from nitrogen to phosphorus.

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