Exploiting natural abundance 13C-15N coupling as a method for identification of nitrogen heterocycles: practical use of the HCNMBC sequence.

In this paper, we detail the results of (1)H-(15)N correlation data obtained via (13)C-(15)N coupling at natural abundance on a number of classes of azoles including pyrazoles, imidazoles and triazoles. The experiment produces data that is highly complementary to direct (1)H-(15)N HMBC type correlations in that it can provide (15)N chemical shift data for nitrogen that may not show up in the HMBC. This is particularly advantageous in the triazoles where (15)N chemical shift can be diagnostic of regiochemistry. Because of the consistency in JCN values among the azoles, the experiment produces distinctive correlation patterns that can be used for identification of regiochemistry. The experiment can also be used to directly measure (13)C-(15)N coupling constants.