Incorporating BIRD-based homodecoupling in the dual-optimized, inverted ¹ J_CC 1,n-ADEQUATE experiment

1,n-ADEQUATE is a powerful NMR technique for elucidating the structure of proton-deficient small molecules that can help establish the carbon skeleton of a given molecule by providing long-range three-bond ¹³ C─¹³ C correlations. Care must be taken when using the experiment to identify the simultaneous presence of one-bond ¹³ C─¹³ C correlations that are not filtered out, unlike the HMBC experiment that has a low-pass J-filter to filter ¹ J_CH responses out. Dual-optimized, inverted ¹ J_CC 1,n-ADEQUATE is an improved variant of the experiment that affords broadband inversion of direct responses, obviating the need to take additional steps to identify these correlations. Even though ADEQUATE experiments can now be acquired in a reasonable amount of experimental time if a cryogenic probe is available, low sensitivity is still the main impediment limiting the application of this elegant experiment. Here, we wish to report a further refinement that incorporates real-time bilinear rotation decoupling-based homodecoupling methodology into the dual-optimized, inverted ¹ J_CC 1,n-ADEQUATE pulse sequence. Improved sensitivity and resolution are achieved by collapsing homonuclear proton-proton couplings from the observed multiplets for most spin systems. The application of the method is illustrated with several model compounds.