Effects of misoptimization of the BIRD pulse on one-bond modulation effects in long-range heteronuclear chemical shift correlation spectra

BIRD pulses have been shown to provide an effective means of decoupling one‐bond modulation of long‐range response intensity. It is not possible to optimize the BIRD pulse effectively when there is a range of one‐bond coupling constants. To examine the effects of misoptimization of the fixed delays (τ) in the BIRD pulse, the simple alkaloid norharmane was employed. Long‐range heteronuclear correlation spectra were recorded using a modified pulse sequence containing a BIRD pulse midway through the Δ2 interval. The experiment was optimized for 10.3 and 11.1 Hz, which correspond to a valley and a peak in the response intensity curve when the experiment is performed without the BIRD pulse midway through Δ2. The delays in the BIRD pulse were variously optimized for values ranging from 80 to 175 Hz. The results suggest that the BIRD pulse is effective in decoupling one‐bond modulations of response intensity even when the τ delays are grossly misoptimized for the one‐bond coupling constantin question.