Measurement of J(H,H) and long-range J(X,H) coupling constants in small molecules. Broadband XLOC and J-HMBC
New methods for the measurement of homonuclear J(H,H) and heteronuclear long-range J(C,H) coupling constants are presented. The heteronuclear and homonuclear coupling constants are measured by schemes based on J-HMBC and XLOC, respectively, and they all employ a low-pass J filter to eliminate one-bond J(C,H) responses. The J-HMBC experiments are automatically broadband in their excitation over a range of J(C,H) coupling constants whereas the broadband feature for XLOC is achieved by employing the approach used in broadband HMBC.
2J,(3)J-HMBC: A new long-range heteronuclear shift correlation technique capable of differentiating (2)J(CH) from (3)J(CH) correlations to protonated carbons
The development of a series of new, accordion-optimized long-range heteronuclear shift correlation techniques has been reported. A further derivative of the constant time variable delay introduced in the IMPEACH-MBC experiment, a STAR (Selectively Tailored Accordion F(1) Refocusing) operator is described in the present report. Incorporation of the STAR operator with the capability of user-selected homonuclear modulation scaling as in the CIGAR-HMBC experiment, into a long-range heteronuclear shift correlation pulse sequence, (2)J,(3)J-HMBC, affords for the first time in a proton-detected experiment the means of unequivocally differentiating two-bond ((2)J(CH)) from three-bond ((3)J(CH)) long-range correlations
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