NMR experiments for determination of coupling constants between equivalent atoms
Recently, two new pulse sequences for determination of coupling constants between equivalent atoms were developed. Both methods utilize one-bond hydrogen-carbon coupling for creation of effective chemical shift difference. The first method, SYMONA (SYmmetrical MOlecules Natural Abundance double-quantum experiment), uses indirect detection via hydrogen and possesses good sensitivity. It is mainly suitable for determination of large single-bond carbon-carbon couplings in symmetrical molecules. On the other hand, the STRONG INADEQUATE experiment uses direct carbon detection and is suitable for measurement of small couplings between equivalent carbon atoms over several bonds. STRONG INADEQUATE works superbly for nJCC, where n ≥ 3. Then the resulting pattern in F1 dimension is reduced to a simple antiphase doublet with nJCC separation. This pattern is preserved even when the symmetrical HC···C’H’ system is coupled to other hydrogen atoms. This is the main advantage of the STRONG INADEQUATE experiment compared to other experiments for determination of coupling constants between equivalent carbon atoms.
SYMONA, Journal of Magnetic Resonance 2019, 298, 107. DOI:10.1016/j.jmr.2018.12.002
STRONG INADEQUATE, Magn Reson Chem. 2019, 57(12), 1107.DOI:10.1002/mrc.4897