HSQC-TOCSY

HSQC-TOCSY experiments are useful for determining structures of unknown compounds via multiple bond correlations. By varying mixing time, it is possible to tune these experiments to short and long heteronuclear correlations. In the example of menthol below, the first spectrum shown in blue was acquired with a short mixing time of 5 ms. Only 1-bond and 2-bond proton correlations are observed for C1 at 72 ppm in this spectrum: C1-H1a, C1-H6e (weak), C1-H2a and C1-H6a. On increasing the mixing time to 30 ms (shown in purple) and then to 60 ms (shown in red) longer correlations  can be detected, e.g., C1-H4e and C1-H4a.