1. Purpose

For the observation of nitrogen, ¹⁵N with I = 1/2 is the isotope of choice, despite its low natural abundance (0.37 %) and low NMR sensitivity; its receptivity as compared to ¹³C is only 0.022. Additionally one has to take into account that under the conditions of ¹H broad-band decoupling a decrease in intensity may occur due to a negative NOE effect resulting from the negative gyromagnetic ratio of ¹⁵N. This problem may be circumvented using the inverse gated ¹H decoupling technique (see Exp. 4.13). However, the preferred methods for direct observation are those with polarization transfer, such as the INEPT [1] or DEPT sequences (see Exps. 6.7 and 6.9, respectively), which may be performed with or without ¹H broad-band decoupling and can be tuned either to ¹J(¹⁵N,¹H) or to ²J(¹⁵N,¹H) / ³J(¹⁵N,¹H). Currently, nitrogen is observed in the inverse mode with gradient selection as described in Experiment 12.21. Here we describe the forward DEPT experiment on formamide with ¹H broad-band decoupling.

2. Literature

G. A. Morris, J. Am. Chem. Soc. 1980, 102, 428–429.
W. Witanowski, L. Stefaniak, G. A. Webb, Annu. Rep. NMR Spectrosc. 1993, 25, 1–480.
S. Berger, S. Braun, H.-O. Kalinowski, NMR Spectroscopy of the Non-Metallic Elements, Wiley, Chichester, 1997.
J. Mason, L. F. Larkworthy, E. A. Moore, Chem. Rev. 2002, 102, 913–934.
R. Marek, A. Lycka, Curr. Org. Chem. 2002, 6, 35–66.

3. Pulse Scheme and Phase Cycle

Proton-decoupled nitrogen-15 DEPT pulse sequence and phase cycle