Accordion BIRD‐HMBC experiments: improved one‐bond correlation suppression in accordion heteronuclear multiple‐bond correlation‐type experiments

Modifications of the BIRD‐HMBC experiment, in which the accordion principle and a constant time period have been introduced, are presented. With the simple accordion BIRD‐HMBC, the use of a BIRD r, X element in the middle of the variable long‐range couplings evolution period efficiently eliminates unwanted 1 J CH signals and samples a broad range of long‐range heteronuclear couplings. While the accordion BIRD‐HMBC experiment shows reduced F 1 modulation, superior suppression of unwanted 1 J CH signals and sensitivity comparable to the ACCORD‐HMBC, the addition of another constant time period suppresses F 1 modulation due to 1 H‐ 1 H coupling, while preserving the excellent suppression of unwanted 1 J CH signals. The constant‐time (CT) accordion BIRD‐HMBC experiment combines sensitivity similar to the CIGAR‐HMBC and superior suppression of unwanted 1 J CH signals. Results of identically optimized ACCORD‐HMBC, accordion BIRD‐HMBC, CT accordion BIRD‐HMBC and CIGAR‐HMBC experiments performed on a sample of strychnine are compared and discussed. Copyright © 2006 John Wiley & Sons, Ltd.