Pii: 0022-2364(80)90083-9

A recent communication (I) has suggested a method of studying 13C-13C couplings in samples with the natural 13C abundance by suppressing the strong cemral resonance from molecules containing a single isolated 13C nucleus, revealing the weak satellite signals from the coupled 13C-13C systems. Excellent suppression ratios were achieved by momentary conversion of the magnetization from coupled spins into double-quantum coherence (2,3), exploiting the characteristic phase properties of the latter. The principal restriction on the generality of this technique arises from the condition for optimum transfer into double-quantum coherence (4,5). For the case of weakly coupled spins, this condition is