Suppressing One‐Bond Correlations in HMBC Spectra: Improved Performance for the BIRD–HMBC Pulse Sequence

An improved version of the BIRD–HMBC experiment is proposed. In comparison to the original version, the filtering (suppression of ¹ J_CH signals) is accomplished using a double tuned G‐BIRD filter positioned in the middle of the long‐range correlations evolution period. Compensation of offset dependence by replacing the rectangular 180° pulses with the broadband inversion pulses (BIPs), with superior inversion performance and improved tolerance to B₁ field inhomogeneity, significantly improves the sensitivity of the original BIRD–HMBC experiment. For usual one‐bond coupling constants ranges (115–180 Hz), optimal results are easily obtained by adjusting the delays, δ, of the BIRD elements to an average J value. For larger ranges (e.g. 110–260 Hz), the use of a double tuned G‐BIRD filter allows excellent suppression degrees for all types of one‐bond constants present in a molecule, superior to the original scheme and other purging schemes. These attributes make the improved version of the BIRD–HMBC experiment a valuable and robust tool for rapid spectral analysis and rapid checks of molecular skeletons with a minimum spectrometer time. Copyright © 2009 John Wiley & Sons, Ltd.