HSQC-TOCSY


The HSQC-TOCSY (Heteronuclear Single Quantum Coherence-Total Correaltion Spectroscopy) is a 2D TOCSY that has been resolved into the carbon dimension. This is especially useful when overlap in the proton spectrum prevents analysis since often the corresponding carbons will be resolved. Cross peaks are seen between all J coupled protons in a spin system and each carbon in that spin system.


Below is a spectrum of sucrose taken at 500 MHz. Notice the patterns of the two spin system groups designated in red and green representing the two sugar moieties. The oxygen between the two rings breaks up the magnetization transfer between the two groups. To interpret the HSQC-TOCSY spectrum, one should start with the direct correlation HSQC peaks. For example, in the HSQC the 1 (anomeric) proton and carbon are at 5.42 ppm and 92 ppm, respectively. TOCSY then transfers proton signal to coupled protons such as the 2, 3, 4, and 5 protons. These transfered signals appear at the 1 carbon frequency of 92 ppm. By looking at this anomeric carbon frequency, one can see all the protons coupled to the anomeric proton. There is no overlap problems as there would be in the proton-only 2D TOCSY - the 5, 6', and 6 protons are all very close.