Lab on 90o Pulse Width

You may work in small groups on the lab. Put all your names on the lab report.

Put in the 1-98 sample and setup for H-1. Change rg to 30. Tune the instrument if it is needed. Obtain the spectrum as usual but process the data in NUTS using a2 and phase it-ap. Do it with the default pw (17.5 ms) at first. Use dc in nuts to adjust the spectrum to the middle of the screen so you can see negative peaks (by adjusting the left scroll bar) and set the vertical scale so that this spectrum is about 80-90% of full scale (by adjusting the right scroll bar). After this adjustment hit the enter key to return to the main menu. Then fix the scale with FS command.. Plot the spectrum -pl.

Now change the pw in pnmr to 3*the default ie pw =52.5 ms. Process with the a2 command. Do not phase, do not use the FS command. Do not change the scale. Plot it. It should be about the maximum negative spectrum.

Now do about 5 other pw's (such as 5, 10, 25, 35, 70) to get a relatively smooth curve when height of any peak is plotted vs pw.

Your write up should include your conclusion as to the correct 90o pulse width. As well as an explanation as to how you determined it.

The 90^o pulse width for an instrument is 7 microseconds. Where will the magnetic vector of the nucleus (initially on the z axis) end up immediately after x axis pulses of the following times ? In each case the pulse will be done after the system has come to equilibrium on the z axis.

a) 7 microseconds

b) 14 microseconds

c) 28 micoseconds.

d) if the detector (located in the xy plane) is turned on which of the above pulses will give the maximum signal.

Computer Lab Work

Nuclear Spin Program.

You can download the zipped file on your PC by googling NMRSPIN.zip.. Download it to your desk top. Unzip the program in the usual way on your computer. If you are using a computer at Marshall, just click on the NMRSPIN.zip icon and the winzip program will come up. Under the actions menu "extract" the two files of NMRSPIN.zip to the desktop.

Click on the SSS.exe icon to enter the SSS program. Doing the following exercise is suppose to get you to visualize what is happening to the magnetic vectors during an NMR pulse experiment. Change the directions all you want as long as you keep that in mind.

Under the SETUP menu enter the single spin system. Under the SETUP menu set the PARAMETERS to about t1=2 s t2= 2s frequency = 2 Hz. Under the OPTIONS menu: select the labels, select relaxation on, and turn on the animation (.5 ms update).

1. Give your system a 90 degree pulse on the x axis. What happens to the proton magnetic vector?

Give it another 90 degree pulse on the x axis. What happens to the proton magnetic vector?

Give it 2 more 90 degree pulses. What happens to the proton magnetic vector?

Return the vector to the z-axis (RESET under the COMMANDS menu) and give it a 90 degree pulse on the y axis. What happens to the proton magnetic vector?

2. Return the vector to the z-axis (RESET under the COMMANDS menu) and give it a 90 degree pulse on the x axis. Choose a DELAY of 8 s (be sure it is s and not ms) under the ÇOMMANDS menu. Repeat this but now watch the third box down from top on the left. This is what the detector in the sees.Draw it out.