Abstract: Two low-pass J-filters are introduced into HMBC experiment to suppress all direct J-coupling peaks and do away with the interference of direct J-coupling peaks and long range J-upling peaks which may occur in HMBC spectra of some molecules. Theoretical analysis and experiments show that the purpose of suppressing all direct J-coupling peaks can be achieved with almost no loss of intensity of long range J-coupling peaks.

Key words: Low-pass, J-filter, HMBC experiment