Fluorine and nitrogen containing organic compounds are often found in a variety of fields such as pharmaceutical and material sciences. Such compounds show unique properties based on their conformations and orientations, which are often induced by hydrogen bonds between N-H and F atoms. Therefore, analysis of molecular conformations and inter-molecular interactions are important. Here, we report 14N decoupled 1H–19F HOESY (hetero nuclear NOE) for fluorinated benzanilide (1) as a demonstration.
Measurements of 14N decoupling 1H–19F HOESY
It often happens that 1H NMR analysis is prevented with the severe line broadening of 1H signal that is bound to 14N atom. In such a case, the 14N decoupling technique is useful. 1H–19F 1D-HOESY spectra with and without 14N decoupling are shown in Fig.1. Selective excitation was done at F5 (Fig.1: upper) and F6 (Fig.1: bottom), respectively. The amide 1H signal intensity in 1D-HOESY is increased by twice, compared to that measured without 14N decoupling. Since NOE measurements have generally difficulty in low sensitivity, the 14N decoupling technique is useful for observation of cross peaks with 1H–14N signals. 2D-HOESY with 14N decoupling measurement is also available(Fig.2).
Fig.1 Comparison of amide 1H signal intensities in 1D-HOESY spectra with or without 14N decoupling
(upper: selective excitation at F5; bottom: F6).
Fig.2 2D-HOESY spectrum of 1 under the 14N decoupling condition.
Sample: 36 mg fluorinated benzanilide in chloroform-d
Equipment: JNM-ECZ400S with ROYALPROBE™ HFX※
※Special modification for 14N nuclei required.
G. N. Manjunatha Reddy, M. V. Vasantha Kumar, T. N. Guru Row, N. Suryaprakash, Phys. Chem. Chem. Phys., 12, 13232–13237 (2010).
L. E. Combettes, P. Clausen-Thue, M. A. King, B. Odell, A. L. Thompson, V. Gouverneur, T. D. W. Claridge, Chem. Eur. J., 18, 13133–13141 (2012).
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