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Investigation of prototropic equilibria by carbon‐13 relaxation time analysis
Author(s) -
Elst L. Vander,
Van Haverbeke Y.,
Maquestiau A.,
Muller R. N.
Publication year - 1987
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260250105
Subject(s) - chemistry , relaxation (psychology) , dipole , spin–lattice relaxation , proton , computational chemistry , hydrogen , crystallography , organic chemistry , psychology , social psychology , physics , quantum mechanics
Quaternary 13 C dipole–dipole spin–lattice relaxation times are used to analyse prototropic equilibria of 2‐acetylbenzimidazole (1) and 4‐azabenzimidazole in DMSO‐ d 6 solutions. For the first compound, fast exchange between the two chelated structures prevails for 13 C relaxation times, whereas proton and 13 C chemical shifts characterize a slow exchange. For 4‐azabenzimidazole, 13 C and 1 H spectra do not exhibit absorptions from structures in slow exchange. Analysis of the T 1 values of carbons 8 and 9 before and after isotopic exchange of the labile amino hydrogen clearly show that the major component of the equilibrium is the 3 H structure.