Generating the List of Chemical Shifts and Coupling Constants
iNMR assists you in the NMR characterization of a compound.
An iNMR document can contain a table of chemical shifts and coupling constants, called the J Manager.
You can fill the table manually, but in general you use the commands (extract or paste) of the J Manager.
Extract is used to analyze first-order multiplets.
Paste is a gateway to other iNMR modules useful for analyzing more complex cases.
Another command, report, generates a formatted list, in a style of your choice.
To Extract the Values from an Easily Interpreted (First-Order) ¹H Spectrum:
-
Process your spectrum and Reference the frequency scale.
If you change the scale reference after extracting the chemical shifts, they will remain uncorrected!
Define the integral regions and normalize the integrals: the area values should be equal to the number of protons from which each signal arises. -
Perform the Peak-Picking.
It is important to select the correct number of peaks.
For example, a doublet of triplets consists of 6 peaks.
If you have picked an extra peak, such as an impurity, delete that label.
When a coupling constant is small, it is necessary to resort to a resolution enhancement, otherwise peak-picking cannot find all the lines. After you have extracted the couplings, you can remove peak-picking and/or the resolution enhancement without affecting the extracted values.
If the peaks are resolved, but the multiplets are not separated, you should perform a selective peak-picking for each multiplet before point 4 below and delete it before going to point 5. - Choose View > J Couplings. This command opens the J Manager for the current document.
- Select a multiplet. Press the e key (lowercase) or click the extract icon. A new entry appears in the J Manager. Change the name (first column) if you like. The same name appears on the plot, above the same multiplet.
- Repeat for all multiplets and fill the table. If a multiplet cannot be resolved, only the chemical shift range will be reported.
- Check for consistency. Two coupled nuclei have, in theory, the same coupling constant. You can keep any experimental discrepancy, or overwrite the value that you think is less reliable with the constant measured from the partner. The table is editable.
- To substitute two inconsistent couplings with their average value, select the corresponding rows, then click match. To undo, click the undo icon twice.
- When you click Report, a preview of the list appears at the bottom of the J Manager window. You can select a different reporting style with the icon Style. If you do not know which one to choose, you can try them all. When you have set a style for proton spectra and another style for heteronuclear spectra, they will be remembered for future sessions.
- What you see is already on the clipboard. You can paste it into a Word document, for example.
- To reproduce the same information, graphically, on the plot, click graph.
If the selected region doesn't contain any frequency label, the command “extract” performs an instantaneous peak picking (not visible). You can put a horizontal threshold on the spectrum, just like with the manual peak-picking. If you do not select a region, the command “extract” will process, one by one, the integral regions, as if they had been selected. Where there is no frequency label, the instantaneous peak-picking will be performed.
If nothing is selected, no integral is found, and the nucleus is not ¹H, the peak-picking labels are used as the source (all signals considered as singlets).
To delete an entry from the table, select (Mac) or check (Windows) it, then click remove.
To observe closely the multiplet corresponding to the selected row, click reveal.