BIRD-J-resolved HMBC and BIRD-high-resolution HMBC pulse sequences for measuring heteronuclear long-range coupling constants and proton-proton spin coupling constants in complicated spin systems

Efficient pulse sequences for measuring long-range C-H coupling constants (J(C - H)) and proton-proton spin coupling constants (J(H - H)), named BIRD-J-resolved HMBC and BIRD-high-resolution HMBC, respectively, have been developed. In spin systems possessing a secondary methyl group positioned between protonated carbons (e.g.-CH(2)-CH(CH(3))-CH(2)-), the methine proton splits in a complicated fashion, resulting in difficulty in the determination of its spin coupling constants. For easy and accurate measurements of the long-range J(C - H) and J(H) (-) (H) in such a spin system, the BIRD pulse [90 degrees x(H)-180 degrees x (H/C)-90 degrees (-x)(H)] or [90 degrees x(H)-180 degrees x(H/C)-90 degrees (-x)(H)180 degrees x(C)] is incorporated into the J-resolved portion of the pulse sequence. As a result, the above secondary methyl group can be selectively decoupled, providing simplified cross-peak patterns, which are suitable for the accurate measurements of the long-range J(C) (-) (H) and J(H) (- H). Copyright (C) 2011 John Wiley & Sons, Ltd.