Chem 325
Name:________________________
Practice Exam #1
This exam contains six questions. Answer all questions in the space provided. All questions are of equal value.
1. Give a clear definition of each of the following terms:
(i) allyl cation:
(ii) wavenumber:
(iii) an IR-inactive vibration:
(iv) anti-Stokes line:
(v) Fourier transform:
(vi) metastable ion:
(vii) an asymmetric vibration:
(viii) polarization ratio:
(ix) Nujol mull:
(x) a base peak:
2. The lab instructor found a flask containing a cloudy liquid, labeled only “Compound X”. She ran a quick EI mass
spectrum, shown below. She immediately knew what the compound was.
(a) What is Compound X? Is there any uncertainty in the structure?
(b) Suggest structures for the fragments at m/z 136, 107, 93, and 57. Why is the m/z 57 peak so intense?
Chem 325 Practice Exam
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3. A synthetic route to alkynes is by a double dehydrohalogenation of alkyl dihalides. A student attempted to convert
trans-2,5-dimethyl-3-hexene to 2,5-dimethyl-3-hexyne by adding bromine across the double bond, then doing a
double elimination. The mass, infrared, and Raman spectra of the major product are shown below:
Br
Br2
KOH
heat
C
C
+ 2H2O + 2KBr
Br
IR
Raman
(a) Do the spectra confirm the right final product? Explain what spectral evidence the desired product should show.
(b) Identify the isolated product. Provide spectral assignments to support your structure.
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4. (a) Determine the index of hydrogen deficiency for the following formulas and provide a chemically reasonable
structure to match the formula
(i) C7H7NO
(ii) C13H9N2O4BrS
(b) Two common laboratory experiments are shown below. In each case, describe how the IR spectrum of the
product would differ from that of the reactant. Give approximate frequencies (wavenumbers) for distinctive
peaks.
CH3
CH3
C
C
OH
OH
CH3
H3C
H2SO4
H3C
C
CH3
C
O
A
CH3
OH
B
O
H
CH2OH
NaBH4
CH3OH
C
D
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5. An unknown sample, thought to contain only carbon, hydrogen and oxygen, was subjected to combustion analysis.
A 45.28 mg sample was burned, producing 99.48 mg carbon dioxide and 23.28 mg water.
(a) Determine the percent composition (by mass) of the unknown.
(b) Determine the empirical formula of the unknown.
(c) The EI mass spectrum showed the molecular ion at m/z 420. Determine the molecular formula.
(d) How many phenyl rings could this compound contain?
Chem 325 Practice Exam
6. Use the spectra below to identify the functional groups and give a molecular structure. Explain how the data
supports your structure.
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