Localization and transfer of protons between nitrogen-15 atoms of meso-tetraphenylporphine probed by nuclear Overhauser effects and dipole-dipole relaxation times

1984 ◽  
Vol 106 (2) ◽  
pp. 292-298 ◽  
Author(s):  
Jurgen Hennig ◽  
Hans Heinrich Limbach
Keyword(s):  
Relaxation Times ◽  
Dipole Relaxation ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects

Relaxation Processes in the N-Methyl Group of 1,2,2,6,6-Pentamethylpiperidine

1990 ◽  
Vol 43 (2) ◽  
pp. 447 ◽  
Author(s):  
ID Rae ◽  
ML Woolcock
Keyword(s):  
Relaxation Times ◽  
Spin Rotation ◽  
Relaxation Processes ◽  
Methyl Group ◽  
Methyl Methyl ◽  
Overhauser Effect ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects

Relaxation times (T1) and methyl-methyl nuclear Overhauser effects were measured for 1H, 13C and 2H nuclei in 1,2,2,6,6-pentamethylpiperidine and its N-CHD2 analogue which was synthesized by LiAlD4 reduction of the N-CHO compound. The relaxation pathways for hydrogens of the N-CH3 group were estimated to be as follows: spin-rotation 0.046 s-1, dipole-dipole within N-methyl 0.069 s-1, and dipole-dipole with the hydrogens of the C- methyls 0.027 s-1. The 1H{1H) Overhauser effect at the N-CH3 was 7.6%.

Positive and negative intramolecular nuclear Overhauser effects in an all-proton system

1968 ◽  
Vol 46 (21) ◽  
pp. 3421-3423 ◽  
Author(s):  
R. A. Bell ◽  
J. K. Saunders
Keyword(s):  
Relaxation Mechanism ◽  
Qualitative Explanation ◽  
Negative Effects ◽  
Dipole Relaxation ◽  
Positive Effects ◽  
Overhauser Effect ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects

The Overhauser effects recorded for the alkaloid ochotensimine (1) show positive effects (area increases) for adjacent protons but negative effects (area decreases) for two protons separated by an intervening proton. A qualitative explanation based on the dominance of a dipole–dipole relaxation mechanism is advanced. The Overhauser effect between geminal protons on an sp2-carbon has been measured.

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