Abstract
Indirect, three-spin effects in the 13C isotopomers arising from abundant or dilute spins are analyzed theoretically and by experiments including mono- and biselective heteronuclear NOE measurements, homonuclear NOE factors, and selective relaxation rates. An extension of the Kuhlmann-Grant-Harris heteronuclear NOE theory to dilute spins allows the determination of direct relaxation rates in AMX spin systems. This method was used successfully for carbon-proton distance measurement in the range of 0.1–0.4 nm in small, rigid, isotropically reorienting organic molecules even in the presence of negative, indirect NOE. The first example of such effects at quaternary carbons in their natural abundance is presented.
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