Two-dimensional (2D) NMR spectroscopy is often used to provide through-bond (J-coupling) or through-space (NOE) correlation. These correlations, shown as "crosspeaks" in the spectrum, can be analyzed to examine detailed molecular structure. In a 2D experiment, the direct detection dimension is usually 1H while the indirect (transient) dimension could be 1H, 13C, 15N, 31P, or other nuclei. The low sensitivity of the broadband nucleus is overcome by coherence transfer with 1H and encoding their chemical shift in the indirect dimension. The advantage of 2D NMR also lies in its ability to resolve ambiguous or overlapping resonances resulting from one nucleus (i.e 1H) along the indirect dimension of another nucleus (i.e. 13C). A close analogy of the resolving power of multi-dimensional NMR is the way we define the address of a location (i.e., longitude and latitude, or country, state, city, street, house number, etc.) that uniquely defines its position on Earth.
2D experiments are naturally more complex than typical 1D experiments because more pulses and parameters are involved and good spectrometer stability is required due to the longer running time. The following are necessary for good-quality 2D data, among others:
Good suppression of artifacts and function of the pulse sequence may also require calibration of certain pulses with your own sample due to solvent sensitivity of the pulse width (90, 180 degree etc).
While newer spectrometers (such as the Varian 600, Bruker 800, and Agilent 400) have electronic routing and require no re-cabling, older Varian spectrometers, including our 500, require a recabling for the X channel if the indirect dimension involves X nucleus.
NMR500 is equipped with a FTS temperature regulation unit, pulsed field gradients, waveform generators and gradient probes. It is capable of performing most 2D experiments. Data quality is mostly adequate for routine work. The Varian 600 is most suitable for most 2D-4D NMR because it is set up with an inverse detection probe that provides the best 1H sensitivity.
Setting a 2D experiments on the Varian system usually involves setting the following hardware and additional parameters compared to a 1D experiment, regardless of the experiment:
Spectral width in the indirect dimension (sw1) should be kept just enough to enclose all signals so that good resolution can be achieved wth the same number of ni points.
How a 2D experiment deals with phase detection in the indirect dimension (via phase parameter) is experiment specific, and may have multiple choices for an experiment. The setup also involves setting experiment specific parameters, such as NOESY mixing time, recycle delay etc, although the default setting in the parameter files should be good for most samples. See specific experiment procedures for details.
Updated, Jan 2019, H. Zhou