How to Fit an Homonuclear Correlation experiment [Exchange]

 Example :  1H 2D exchange spectrum fitted as an homonuclear correlation  

By "homonuclear correlation" we assume that both dimensions (F1 & F2) of the spectrum have the same characteristics. This will be the case for the exchange experiments, no matter the recoupling mechanism, this will not be the case for a Double Quantum/Single Quantum correlation (because the two dimensions are not equivalent) nor for a LG/MAS correlation because the lines do not have the same characteristics in both dimensions.

 Step 1 : Fit of a 1D spectrum containing all the peaks that will be present in the 2D spectrum.

This step is not necessary but can simplify the process of fitting the 2D dataset.

If you need you can learn more about fitting a 1D spectrum with Gaussian/Lorentzian lines have

 Step 2 : Switch to the 2D dataset.

Having the 1D spectrum and fit loaded, just go the the [Menu/File/Open] and open the 2D dataset (*.rr files for Bruker).


Load in the 2D dataset [Menu/File/Open] and open the 2D dataset (*.rr files for Bruker) and load the 1D fit parameters [Menu/Decomposition/Load Other]

Step 3 : Switch the decomposition mode from 1D to 2D

In the lef panel, change the fitting mode from "Fit 1D" to "Fit 2D" (if you do not see this option, enlarge the dmfit window to make it appear).

Step 4 : Call the Cross Peaks dialog box and set values

  1. Call the "Cross Peaks dialog box" by clicking the button that appeared in the left panel.

  2. If the button at the top of the window is labeled "Hetero" you will fit an heteronuclear correlation, click it to switch to "Auto" Autocorrelation mode.

  3. Click on "Init from 1D" to set default values or enter the values you want in the different cross peaks intensities

  4. Click Ok to get back to the main window

Remark : all no zero values for cross-peak intensities will be optimised in the fitting process, future development should allow fixing or freing all the individual lines. The display of the Cross-Peak dialog is rather crowded, it can handle up to 50 lines and 2500 cross-peaks.

Step 5 : Optimising the intensities of cross-peaks

  1. Same rules apply for fitting 2D experiments and 1D experiment except that the 1D Amplitude is not taken into account. All boldface paramters will be optimised. Be carefull that this could lead to lengthy computations and minimise the number of free parameters if you can.

  2. Click the [Optimize] button to optimize the current solution (all boldface parameters will be adjusted as well as the non zero cross-peaks)

  3. Click on "Init from 1D" to set default values or enter the values you want in the different cross peaks intensities

  4. Click Ok to get back to the main window

Step 6 : Reporting and Saving

Fit parameters can be saved in machine readable binary format [Menu/Decomposition/Save Fit] or [Menu/Decomposition/Save as Fit] and thus retrieved later exactly in same state.

Parameters can be reported in human readable format by clicking the [Report] button to report the current line paramters in a dialog box from which you can Select/Copy and further Paste word processing or SpreadSheet programs.

Tricks and techniques

If your dataset is symmetric as compared to the diagonal of the spectrum, you can speed the computation by symmetrizing your dataset [Menu/2D/Symetric] and treating only half of the off-diagonal crosspeaks [Check the "symmetric autocorrelation" checkbox in the cross-peaks dialog].