14N NMR as a General Tool to Characterize the Nitrogen-Containing Species and Monitor the Nitration Process

The usefulness of 14N NMR spectroscopy was highly underestimated compared with 15N NMR, which usually required tedious and expensive 15N-labeling manipulations. It is of great significance to make the 14N NMR spectroscopy convenient and useful considering 14N nuclei's high natural abundance of 99.6%. Herein, lots of efforts have been made to generalize routine 14N NMR to characterize nitrogen-containing species by tuning the balance between the solubility and viscosity of the samples. Satisfactory 14N NMR spectra of more than 60 nitrogen-containing compounds have been recorded, and the chemical shifts and the peaks' full width at half-maxima of more than 10 nitrogen-based functionalities have been summarized. Successful monitoring of the ortho-selective nitration of aniline has been demonstrated using the 14N NMR protocol developed in this paper, which will help realize the visualization of nitration processes in the industry.