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 CH coupling constants ( J CH ) and proton‐proton spin coupling constants ( J HH ), 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 CH and J HH in such a spin system, the BIRD pulse [90° x (H)− 180° x (H/C)− 90° (− x )(H)] or [90° x (H)− 180° x (H/C)− 90° (− x )(H)180° 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 CH and J HH . Copyright © 2010 John Wiley & Sons, Ltd.