multiplicity.doc >>>9/16/1998

2. Polarization transfer always involves high power pulses of both ¹³C and ¹H and delays related to the inverse of the 1-bond carbon-hydrogen J coupling constant, ¹J_C-H. Implementation is straightforward starting from parameters appropriate for routine ¹³C observation because many of the parameters are already set correctly.

1. The ¹³C 90 degree pulse time and corresponding power level
2. The ¹H pulse 90 degree pulse time and power level needed for composite pulse decoupling

1. The name of the pulse program
2. The 90 degree pulse time and corresponding power level for the high power ¹H pulse -These parameters will be listed in the spectrometer notebook. (In the case of ¹³C observation, even these parameters will probably be correct in the default parameter files, but you must check since they are not actually used for routine observation.)
3. 1J_C-H

1. The full DEPT experiment involves three different experiments. These are usually called DEPT45, DEPT90, and DEPT135 because the final high power proton pulse is a 45 degree, a 90 degree, and a 135 degree pulse, respectively. The results of these experiments are:

 

1. All quaternary carbons (and deuterated solvent signals) are absent from all DEPT experiments.

2. The DEPT45 produces positive signals for all CH, CH₂, and CH₃ carbons.

3. The DEPT90 produces positive signals for CH carbons; all others are absent.

4. The DEPT135 produces positive signals for CH and CH₃ carbons and negative signals for CH₂ carbons.

 

2. The DEPT45 is used to determine the phase to be used for the rest of the DEPT spectra. The phase constants of the DEPT45 are applied to the DEPT90 and DEPT135 spectra with the pk command (usually in the combined efp command).

1. From parameters for a routine ¹³C spectrum, make a new data set.
2. Change the pulse program name to dept45.js, dept90.js or dept135.js as appropriate.
3. Set the parameter p3 to the 90 deg pulse time for ¹H high power pulse and the parameter dl0 (the second character is the letter l, not the number 1) to its corresponding power level (expressed as attenuation from full power), usually 1.00 db. (See spectrometer notebook.)
4. Set CNST2 to the one bond J value. A value of 135 to 145 Hz is a reasonable choice for ¹J_C-H .
5. Type rga to determine the appropriate receiver gain. Do this from the DEPT45 and use the same value for the DEPT90 and DEPT135. If you plan to acquire only the DEPT135, do the rga from DEPT135 parameters.
6. Full phase cycling requires that NS be a multiple of 32. If fewer scans are required, it is best to use the usual multiple of 8. At least 2 dummy scans (DS) are probably a good idea.
7. Once the parameters are set, start the acquisition with the usual zg command.
8. When processing the data, phase the DEPT45 spectrum with all positive peaks. If the other parameter sets are created after the DEPT45 has been phased, the correct phase constants will be a part of the parameters of the new data set. If they were created before the correct phasing was determined, simply determine the values for the parameters, PHC0 and PHC1 and enter them into the other data sets. Then apply them to the other data sets with the efp command.
9. If you have acquired your data with the same data set name but increasing expno's, a convenient way to step through the spectra is to use the dual display. Select the "button" labeled dual. A window will appear in which you must specify the name of the second data set for display. (It defaults to the next higher procno, which is not what you want, so you will have to input the correct expno and procno, then select SAVE.) In the dual display, the "buttons" on the upper left affect both spectra. The "buttons" below that area affect spectrum 1 (i.e. the one from which you entered the dual display) and the next set of "buttons" below that affect spectrum 2. Initially the spectra will be on top of each other so move them around where both can be seen well. Step through the rest of spectra by selecting the "button" labeled E­ ( to increment the expno).

5. There is an automation routine that will acquire all the DEPT spectra and process them for you. This routine assumes that you may want to do long term signal averaging and will ask how many cycles of the entire acquisition you would like to have. The total number of scans will be NS times the number of cycles you input. To use this routine:

1. From parameters for a routine ¹³C spectrum, type deptcyc.js. You will be asked to input all the appropriate pulse times and power levels and a J value. Most will already be correct from the default ¹³C parameters but check the values in the spectrometer notebook.
2. If you want to stop the acquisition before all the cycles are complete, type depthalt. The data acquisition will stop at the end of the current cycle and all files will be processed.

1. The dept90 and dept135 data sets must have the same name but different experiment numbers from the ¹³C spectrum from which this routine is run.
2. Read in the data for the ¹³C spectrum, then type edg. Under "edit peak labels", change "multiplicity labels" to yes, then save the menus. Type deptmult.js. A window will come up in which you define the dept90 data as the 2^nd data set and the dept135 data as the 3^rd data set. (This is the "edc2" window used to define the 2^nd and 3^rd data sets for the dual display.) You will also be asked to specify a % variation in the dept90 data. The default of 50% is probably fine if your pulse repetition rate is not too fast compared to the ¹H T₁ values. A plot of the 13C spectrum will now have the following on the peak labels: Q=quartet, T=triplet, D=doublet, S=singlet, U=unknown. Solvent and reference peaks should not have multiplicity labels.

1. CH and CH₃ carbons are positive and quaternary and CH₂ are negative.
2. In fact, the absolute sign is arbitrary, the important point is that the signs of CH and CH₃ carbons are opposite of quaternary and CH₂ carbons.