ARMSTRONG
FOOTHILL COLLEGE
NMR ACQUISITION OF AN UNKNOWN SOLID
Today you will acquire a 1H NMR spectrum of a solid unknown. You must acquire the
spectrum, make copies for your notebook and for your partner, and then you must use the
spectrum along with the given molecular formula to determine the structure of the
Unknown.
1. Write down your assigned unknown and weigh out 30 mg into a clean and dry test
tube.
2. Determine the 0.6 mL mark on a disposable Pasteur Pipette by drawing up 0.6 mL
of water into a clean pipette, and marking the level with a Sharpie. Use a second
clean and dry pipette and mark the 0.6 mL level on this pipette by comparing to
the first.
3. When your number is called, you will need to take your sample and the clean, dry
pipette with a bulb to the NMR room. You will then add deuterated solvent to the
test tube and transfer the solution to a clean and dry NMR tube with your
instructor’s supervision. Do not double dip or you will be charged the cost of a
full bottle of deuterated solvent.
4. Using the commands given below under “NMR ACQUISITION: The Basics” you
will acquire and print a proton spectrum of your sample while taking very careful
notes of exactly what you did. The more careful your notes are, the more adept
you will be the next time you attempt to acquire a spectrum.
5. Once your acquisition is complete, you must very carefully dispose of your
sample. Pull straight “up” on the NMR cap to remove it from the NMR tube- it is
fragile and breaks easily. Empty your solution into the Organic Waste container.
You must then return your NMR tube to your instructor, who will wash it for you.
Please be very careful with the NMR tubes- they are very finely machined and
quite expensive!
MOLECULAR FORMULAS OF UNKNOWNS
Unknown #1: C8H9NO2
Unknown #2: C6H5BrO
Unknown #3: C7H5NO3
Unknown #4: C8H7NO3
Unknown #5: C9H11NO
ARMSTRONG
FOOTHILL COLLEGE
NMR ACQUISITION: THE BASICS
SOLID SAMPLE:
Weigh 30 mg of sample into a clean and DRY test tube. If you do not have 30 mg, you may use
less, but let your instructor know how much you weighed out. Obtain a disposable Pasteur
Pipette and bulb and then use a “sharpie” to draw a line on the pipette at the 0.6 mL mark.
Add 0.6 mL of CDCl3 or other deuterated solvent to the test tube containing your solid. Swirl to
dissolve, then transfer the contents to a clean, dry NMR tube.
NEVER “DOUBLE DIP” INTO solvent bottle.
LIQUID SAMPLE:
Weigh 3 drops of your sample into a clean and DRY test tube.
Add 0.6 mL of CDCl3 or other deuterated solvent to the test tube containing your solid. Swirl to
dissolve, then transfer the contents to a clean, dry NMR tube.
NEVER “DOUBLE DIP” INTO solvent bottle.
POSITION THE SAMPLE IN THE SPINNER:
Handling the Spinner with a Kimwipe, insert the capped NMR tube into
the spinner such that the bottom of the tube protrudes from the spinner.
Use the depth gauge at the front of the NMR magnet casing to position
the NMR tube at the correct level before inserting it into the probe.
PLACE SAMPLE INTO PROBE:
Holding the top of the NMR tube, place the tube/spinner in the probe with the AIR ON (the air is
ON when the arrow-shaped valve is directed forward toward the user . The air should be audible)
Turn the arrow-shaped valve counter-clockwise 90° to lower the air so that the sample is allowed
to drop into position.
Turn the arrow-shaped valve another 90° counter-clockwise to increase the air pressure slightly
so that the sample spins
ACQUIRE THE SPECTRUM:
The commands described below represent just a few of the commands that may be
necessary during acquisition and processing of a 1H NMR spectrum. Take careful notes
in your notebook so that you can later acquire an NMR spectrum on your own.
Sitting at the Console, use the mouse to select “aii” from the tabs at the bottom of the
screen.
Enter the following commands at the H1> prompt at the bottom of the blue acquisition
window:
Note: Italics signifies command is optional- applies to new conditions only
Command
Shim<enter>
2<enter>
Action
Applies corrections to magnetic field around
sample to provide a uniform field for a longlasting signal
This is an automated subroutine that requires
approximately 2 minutes to complete
nu H1 <enter>
Sets parameters to default parameters for proton
“one-pulse” acquisition
ns 4
Number of scans = 4
(set to 8 or more if sample is very dilute)
zg <enter>
Zero memory Go acquire
<enter>
Store signal under “pnmrfid” filename
Select “File” from menu then “Carbon” or “Proton” This stores the signal so that it may be processed
then “Documents”
at either one of the two work stations
Give the FID a filename “yourname_experiment”
Save
Move over to workstation, open NMR then open
your file
Select “NMR” from tabs at bottom of screen to
enter white processing window
<enter>
a5
Macro that takes time domain signal and applies
Fourier transformation into frequency domain.
Also performs some signal processing to reduce
noise and correct baseline.
ap
Auto phasing of signal
>zo
use left mouse to select downfield signals only then
type
1
now use right mouse to select upfield signals and
then type
2
<enter>
>PE
use left mouse button and move mouse left and
right to correct phase in region 1 then right mouse
button to correct phase in region 2
<enter>
Hold down left mouse button so cursor is on TMS
signal. Type letter
o
then number 0
<enter>
fb
deselect areas that are NOT baseline by clicking
mouse button to remove them
(pink color will disappear)
l
<enter>
id
c
Using left mouse button, Double click at baseline
to the left of most downfield signal then move
mouse to right of most downfield signal (again at
baseline) and click just once with left mouse
button.
This is a sequence to manually phase signal
Zoom
Defines this downfield region as region a
Defines this upfield region as region 2
Exit zoom
Phasing Command
Exit phasing
Sets TMS signal to zero
This is LETTER O for Offset
This is NUMBER zero for zero ppm
Fix Baseline
LETTER “l” to apply Least squares or
LETTER “c” for polynomial Correction
You will see numbers flash on screen but no other
visible change
Integrate Data
Clear old stops
Selects a region to integrate. Integral should be
displayed above “step” for each integration region.
Repeat the double then single clicks at left and
right, respectively, of each signal in the spectrum
except the TMS signal until all integration regions
have been selected.
Holding mouse at smallest signal suspected to be
part of spectrum, type
V
1
<enter>
p
<enter>
<enter>
Sets integral values relative to a given number
VALUE of “1” implies 1 relative H for that signal.
All other signals will be measured relative to this
value.
Prints spectrum. Type “p” twice for two copies.
Exits integration subroutine