1H-13C HMBC | hmbc
Appliedtothepurposeof1H–13CHMBCexperiments,theheteronuclearlow-passJ-filter(LPJF,Figure4)isapulseelementthatsuppressesthemagnetizationHdassociatedwithlargeone-bondheteronuclearcouplingconstants1JCH,whileleavingvirtuallyunaffectedthemagnetizationHrassociatedwithsmalllong-rangeheteronuclearcouplingconstantsnJCH.Figure4.GeneralschemeforconstructingN-stepslow-passJfilters.Low-passfilteringprocesscanberepeatedandimprovedseveraltimeswithdifferentintervalsτ1,τ2,…inordertoproperlyeliminateall1JCHpea...
Applied to the purpose of 1H–13C HMBC experiments, the heteronuclear low-pass J-filter (LPJF, Figure 4) is a pulse element that suppresses the magnetization Hd associated with large one-bond heteronuclear coupling constants 1JCH, while leaving virtually unaffected the magnetization Hr associated with small long-range heteronuclear coupling constants nJCH.
Figure 4. General scheme for constructing N-steps low-pass J filters. Low-pass filtering process can be repeated and improved several times with different intervals τ1, τ2, … in order to properly eliminate all 1JCH peaks when a wide range of one-bond coupling constants 1JCH is present in the molecule.
The simple one-step low-pass J filter has severe deficiencies if the sample has a wide range of one-bond heteronuclear coupling constants 1JCH, which is practically always the case of organic, inorganic, and biomolecular compou...