Two-dimensional (2D) NMR spectroscopy is a general concept that enables chemical information to be encoded into a second dimension making use of spin-spin interactions like the J-coupling. It is particularly useful to simplify 1D spectra with overlapping signals and to identify coupled chemical groups. While 2D techniques are routinely used at high field they are not exploited on benchtop NMR spectrometer. One of the main reasons for this is the high stability required to sample the data along the indirect dimension. Frequency or phase instabilities between scans result in stripes along the t1 direction also known as t1 noise. Furthermore, the acquisition of meaningful 2D spectra is only possible if the spectrometer provides enough resolution and high signal-to-noise, otherwise the acquisition time for a 2D spectrum can become excessively long.
In this work we demonstrate the performance of 2D NMR on a 1 Tesla permanent magnet benchtop spectrometer. The magnetic field homogeneity of the magnet can be finely shimmed to achieve sub Herz resolution by means of shim coils up to order three, and high field stability is achieved by means of an external lock system. From the large variety of available 2D pulse sequences we tested the performance of J-resolved spectroscopy, correlation spectroscopy (COSY), and double quantum filtered (DQ-COSY). The results presented here demonstrate that 2D NMR is of great assistance for benchtop NMR spectroscopy where the spectrum of small molecules may appear crowded due to the strong coupling limit.