STRONG INADEQUATE, an experiment for detection of small J(C,C) couplings in symmetrical molecules

A new version of the two-dimensional INADEQUATE experiment was designed for detection of small couplings between equivalent carbon atoms separated in the molecule by several bonds, where other techniques fail due to rich line splitting and mutual peak cancellation in many molecules. As the proposed method is suitable for detection of couplings in strongly coupled systems in general, we propose the name STRONG INADEQUATE in the paper. Similar to other methods for detection of couplings between equivalent carbons, the STRONG INADEQUATE experiment utilizes one-bond carbon-proton coupling for creation of the effective chemical shift differences. The STRONG INADEQUATE experiment works superbly for ⁿ J_CC , where n ≥ 3. Then the F1 pattern is reduced to a simple antiphase doublet with ⁿ J_CC separation, and this pattern is also preserved when a symmetrical HC···C'H' system is coupled to other protons. Even in the measurement of ² J_CC couplings, the STRONG INADEQUATE experiment generates a much simpler pattern than the original pulse sequences for measurement of couplings between equivalent carbons.