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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 21, Number 11
BKCSDE 21(11)
November 20, 2000 

Study on Direct Dipolar Effect of Neighboring Protons in Proton Coupled 13C Relaxation Experiment
Hyun Namgoong, Impyo Lee, Jo Woong Lee
The dipolar effect of neighboring protons that are not directly bonded to the carbon of interest on coupled carbon-13 relaxation in a simple organic molecule has been studied by comparing the relaxation behaviors of labeled carbon-13 in Br13CH₂COOH with those in BrCH₂13COOH. Various pulse sequences, such as coupled inversion recovery pulse sequence, J-negative and J-positive pulse sequence, and nonselective and selective proton πpulse sequence, were employed to perform the required coupled spin relaxation experiments. To gain information on various spectral densities, including that of dipolar-CSA cross correlation, the experiments were performed on two different spectrometers, operating, respectively, at 50.31 and 125.51MHz for 13C. The magnitude of CH dipolar spectral densities for BrCH₂13COOH was found to be about 8% of those for Br13CH₂COOH, which means the effect due to the protons not directly bonded to the carbon of interest is small but not completely negligible.
1077 - 1084
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