Office of Research

Center for NMR Spectroscopy

Automated DEPT spectrum

Step 1 – Choosing your solvent and the C13 & DEPT option

Instead of running the C13 spectrum separately from an editing sequence like DEPT you may choose to run both via the C13 & DEPT button on the Setup EXP panel. Once the sample has been locked and shimmed click the C13 & DEPT button to begin. A now familiar Save As dialog box appears to which you choose your AutoLOCK NO and AutoSHIM NO options, fill in the file name and text fields and press the OK and Exit buttons. The following dialog box will appear:

The choices for the C13 spectrum will be familiar to you by now. What is new are the choices for the DEPT editing spectra. The way the data will be acquired and stored is as follows. The C13 spectrum is run first and stored as a sub directory under the filename you gave. The C13 spectrum is processed and plotted and the DEPT spectrum set up and run according to your choices.

The user has only two choices to make in this dialog box for the DEPT parameters. The first is the number of scans for each DEPT edit. The default is the number of carbon scans divided by 3. The DEPT spectrum is usually a factor of almost 4 more sensitive than the straight C13 spectrum so a choice of 1/3 the number of scans will usually yeild good results. The number will ultimately depend on how long it took to acquire a good C13 spectrum and on the degree of editing you wish to do.

The Full edit option results in 4 separate spectra being acquired and processed by a program which yields a plot of 4 spectra, the first being all protonated carbons, the second being just methine carbons, the third being just methylene carbons and the fourth being just methyl carbons. A separate text report gives all protonated carbon shifts and whether they are methine, methyllene or methyl carbons. The CH+CH3 up / CH2 down option acquires only one spectrum which has methine and methyl carbons phased up and methylene carbons phased down. The third selection yeilds a spectrum of just methine carbons and the last selection yields all protonated carbons.

Once the choice has been made push the Ok and Exit buttons to load the choices and quit the dialog box.

Step 2 – Beginning the acquisition

Click on the Acq & Obs tab to review some of the acquisition parameters. You may also want to click the Sequence tab which brings up the panel shown in figure 2.

On this panel reside "sequence" specific parameters such as the size of the scalar J coupling being used, in this case 140 Hz which is a typical aliphatic C-H J coupling. Also not the check boxes for establishing the editing patterns. More about these types of parameter displays will be found in the manual sections on setting up individual or manual experiments.

The NMR pulse sequnce for DEPT is shown below:

Step 3 – Processing and plotting the data

Once the spectra acquired in the automated run have been processed, displayed and plotted as shown below:

A report that also will be displayed is shown below:


Examining the DEPT in more detail

In the automated mode the DEPT spectra are processed and combined in such a way as to give a fully edited set of sub-spectra. To see what the "raw" data looks like press the Process Tab which brings up the following window:

Click on the PROCESS RAW DATA button. What do the resulting spectra look like? How do they compare with the original edited subspectra?

Click on the Display Tab, which will bring up a window like this:

Under the Display subsection click on the CH Only button to display only the CH subspectrum as shown below:

What do the small peaks at 45, 34.8, and 23 ppm in this example signify? Does your spectrum contain small peaks in the CH only subspectrum?

Reprocess the data with the Process for DEPT Analysis option. Click on the Plot Tab to bring up the DEPT plotting options in the window shown below:

Plot out the spectra again using the individual spectra options as well as printing out the analysis report.



If time permits the following section describes how to calibrate the DEPT 1H pulsewidth

The most sensitive parameter in the DEPT experiment is the 1H theta pulse which selects for the different carbon types. To calibrate it do the following:

1) Go to the Sequence Tab and select for XH spins ONLY radio button. 2) Go to the Decouplers Tab and note the value of the High Power pi/2 1H pulse which is the Varian parameter pp 3) Make an array of pp around this value, ie. if the value was 9.5 microseconds make an array which extends from 9.0 to 10.0 in steps of 0.1 4) type go on the command line, when the spectrometer finishes collecting the data go to the Process Tab and click Process Raw Data. 5) type dssh on the command line to display the spectra side to side. The correct 1H pi/2 pulse is where the CH2 peaks are nulled.

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