Experiment 10
Identification of an Aldehyde, Amine, Alcohol, or Ketone
1. Summary
In this experiment, you will be given an unknown that is either an aldehyde, ketone, amine, or alcohol. The
possible unknowns are listed in tables that will be posted in the laboratory. You will determine the boiling point of your
unknown, and using the NMR and IR spectra,
21
classification tests, and melting point of the derivative, you will determine the identity of your unknown.
Il. Procedure
Bring a clean, dry 13 x 100 min test tube to the storeroom manager and trade it for 3 a sample
of your unknown (approximately 2.5g). Your TA will give you copies of the 'H and I C NMR
and IR spectra for your unknown. You should then do the following:
1. Determine the boiling or melting point of the unknown. To determine the boiling point, set up an apparatus for simple
distillation. In this experiment, however, you will not actually distill your unknown, so pay careful attention to the
following description. Use your 25mL pear-shaped flask as a distillation flask. You will actually insert the thermometer
all the way into the flask, so add enough of your unknown to the distillation flask to completely cover the mercury bulb of
your thermometer. Heat the flask until the unknown boils. You should record the boiling point as the temperature at which
the thermometer stabilizes. To obtain a boiling (or melting) point range, subtract 5 'C from the observed temperature to get
a lower limit, and add 10 OC to the observed temperature to get an upper limit. Report this range to your TA who will tell
you if the boiling point or melting point of your unknown is within this range.
2. Determine the functional group present in your unknown using the IR spectrum. BEFORE you come to class, know the
stretching frequencies for carbonyls, O-H, and N-H. By looking at the IR spectrum, you will be able to determine which
of these functional groups is present in your unknown. This will determine which tests you should perform on your
unknown. Check your conclusions with your TA before you begin the tests.
3. Perform characterization tests on your unknowns. All of the reagents will be prepared ahead of
;Z
time for your use. You only need to do those tests required for your functional group.
Z~
Aldehydes/ketones:
alcohols:
amines:
2,4-DNP (642-643), Tollens (644-645), chromic acid (646-647), iodoform
(647-649)
chromic acid (646-647), iodoform. (647-649)
Hinsberg (672-675), HCl solubility (628)
4. Narrow your choices. Find the tables for your functional group and write down all of the compounds in that table whose
boiling/melting points fall within the range determined in step 1. Your unknown will be one of these compounds.
5. Synthesize a derivative. Once you have determined the possible identities of your unknown, you will need to make a
derivative. The type of derivative you make will be determined by the functional group. Choose the derivative that you
think will give you the most useful information. You should recrystallize your solid carefully, since an impure derivative
would give you a low melting point which would be misleading.
Aldehydes/ketones:
alcohols:
amines:
2,4-DNP (642-643), sernicarbazone (650)
3,5-dinitrobenzoate (665, Method A; see experiment 9 for amounts of
reagents)
benzenesulfonamides (678), benzamides (677-678)
6. Use your NMR spectra to help you determine the identity of your unknown. You should interpret the spectra to the best
of your ability. For each set of peaks in the 1H NMR, you should determine chemical shift, integration, and multiplicity.
For each peak in the 13 C NMR, you should determine the chemical shift. See your text for a full description of how to use
this information to detern-iine the structure of your compound.
22
7. Interpret the data in lab, and try to determine the identity of your unknown before you leave the
lab. At least narrow your list to a maximum of five possible compounds.
III. Lab report requirements
Your lab report (due the day scheduled for check-out) should contain the following:
1 . Reference to the procedure of each chemical test and derivative
2.
Melting point or boiling point of your unknown
3.
Results of each chemical test and your interpretation of these results
4. Data table for 'H NMR: For each set of peaks, give the chemical shift, splitting
pattern integration, and your assignment of which proton of set of protons in the
compound give rise to the peak or set of peaks.
5.
Data table for 13 C NMR: For each peak, report the chemical shift and
assignment.
6. Data table for,IR: (assign bands above 1500 crrf) For each band, report position in
wavenumbers, a description of the band (strong, weak, or medium, sharp or broad)
and your interpretation.
7.
Preparation of the derivative (type of derivative and reference to procedure)
8. Melting point of the derivative
9.
Identification of the compound with an explanation of how you arrived at this conclusion