Fig. 1.

Four common placement of hard π pulses in multidimensional NMR. Imperfect pulse with flip angle α or α′ ≤ 180° for ¹H_A/¹H_B and ¹H_N decoupling (A), ¹H_N decoupling (B), chemical shift refocusing (C), and both refocusing and decoupling in INEPT (D). Narrow bars represent 90° pulses, and the flip angles of wide pulses are α and α′ as indicated on the plot. The default pulse phase is +x. Delay Δ is 1/(4J), and J is the scalar coupling between ¹H and ¹⁵N. T is a delay. PFG G1 = (1 ms, 10%), G2 = (1 ms, 20%).