Dr. Xie
32-335
Concept check list for 335 lab
All prelab questions plus the following. Some may overlap.
Exp#1:
1. In the nitration of toluene experiment, what is the function of sulfuric acid ? What is the electrophile
produced in the mixture of nitric acid and sulfuric acid?
2. Which product has higher polarity (dipole moment), o-, m-, or p-toluene? (hint: consider electron
donating or withdrawing properties of methyl and nitro groups, or think about this in terms of
activating and deactivating of the benzene ring)
3. Polar compounds interact with the GC column more strongly (being held up longer). Which
compound is expected to come out of the gc column first (shortest retention time) based on the
polarity difference? Does your prediction agree with what you observed in the lab (check your GC
chromatogram) ?
4. If benzene is nitrated under identical conditions as toluene, which compound, benzene or toluene,
will react faster? Explain.
5. Draw a valid Lewis structure for sulfuric acid. Explain why it is a strong acid based on resonance
theory.
Exp#2:
1. Based on the balanced equation for the reduction of heptanal by NaBH4, the stoichiometry of the two
reagents are 1:4 (check your lab report). Do you know how to calculate limiting reagent and
theoretic and actual yields based on the balanced equation.
2. After the reaction, HCl was added to destroy any excess NaBH4, what is the gas released ? write an
equation that describes this reaction. (hint: identify the acid and base in this reaction based on
electronegativity of bonded atoms)
3. Using IR only, how can you tell if the yield for this reaction is good or poor?
4. Why should the product be dried before taking its IR spectrum? (give at least two reasons)
5. Heptanal came out of the GC column earlier than 1-heptanol. Suggest a reason.
6. In the M.S. of heptanal, what’s the m/e for the fragmentation ion resulting from the McLafferty
rearrangement of the molecular ion?
Exp#3: interpretation of spectra
Be able to elucidate the structure of an unknown organic compound using a combination of IR,
NMR, and MS.
Exp#4:
1. The balanced equation involves 1:3 stoichiometry for reactants. You should be able to calculate
limiting reagents and percentage yield based on the balanced equation.
2. Ether is evaporated in a sand bath before GC analysis. What are the advantages and disadvantages of
using a steam bath vs. a sand bath?
3. In GC chromatogram, cyclohexanone eluted (came out) earlier than cyclohexanol, why ?
4. How many 13C signals can be observed for 4-methylcyclohexanol (draw its chair conformation)?
Exp#5:
1. Describe the procedures of recrystallization of a solid using ethanol as the solvent.
2. If m.p. is taken when the solid is still wet, is the observed m.p. expected to be lower or higher than its
true value? How about its range ?
3. When 1HNMR is taken for a dilute solution of an alcohol, the OH signal shows up ~ 1.0 PPM.
Increasing the concentration of the alcohol shifts the OH signal to 4.0. Explain why.
Exp#6:
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Dr. Xie
32-335
1. In the aldehyde-ketone unknown determination, how can one distinguish an aldehyde from a ketone ?
(chemical test? Spectral analysis ? etc.)
2. What is the most characteristic IR frequency for aldehydes and ketones? How about 13C chemical
shift?
3. When semicarbazide (below) reacts with ketones or aldehydes, which nitrogen reacts? Explain.
O
NH2NHCNH2
Exp#7:
1. Write an aldol condensation mechanism for reaction between propanal and benzaldehyde. Which is
nucleophile in this reaction? Which is electrophile?
2. For b.p. measurement, draw a proper setup for distillation including the correct placement of a
thermometer.
3. For the following conjugated unsaturated product, would you expect the C=O stretching frequency to
be lower or higher than a normal aldehyde C=O. Explain why.
H
CH3CH2
O
C C C H
CH3
Exp#8:
1. What’s the function of aliquot 336, a phase transfer agent ?
2. What is the advantage of using diethylbenzylphosphonate over a normal Wittig reagent ?
3. Why there is no IR peak corresponding to the C=C stretching for tran-stilbene @ 1600 cm-1?
4. Describe two ways of taking an IR spectrum for a solid.
Exp#9:
1. Why should the preparation of Grignard reagent be carried out in anhydrous ether rather than
technical ether ?
2. Can Grignard reagent be prepared using ethanol as the solvent ? why?
3. After the crude benzoic acid was obtained, the ethereal solution was washed three times with 5%
NaOH, why?
4. Where (chemical shift) do you expect to find the COOH signal in 1HNMR? Explain why the H in
COOH is so much deshielded. The peak is usually very broad, why?
Exp#10:
1. Explain why 2,4,6-trinitrophenol is a very strong acid.
2. When a water-insoluble amine is allowed to react with HCl, the resulting product is water-soluble.
Show what the product is and why it’s water-soluble.
Exp#11 General unknown:
1. Be able to explain the following terms: m.p., solubility, and pH.
2. Be able to interpret spectra of IR, MS (isotopes, molecular ion and nitrogen rule, simple
fragmentation including McLafferty rearrangement), and NMR (1H and 13C).
3. Be able to identify possible functional groups employing solubility test. What kind of compounds
will dissolve in the following solutions: aqueous NaOH, NaHCO3, dilute HCl, water, and sulfuric
acid respectively?
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