216 S10-Exam #1 Page 2.
Name _____________________________
I. (3 points) Arrange the following four compounds in order of their Rf values when analyzed by thinlayer chromatography (TLC) on silica gel-coated plates using CH2Cl2 as the developing solvent. No partial
credit is given to this question.
O
H
HO
1
O
HO
3
2
Answer:
<
4
<
<
lowest Rf
highest Rf
II. (9 points) Silica gel thin-layer chromatography (TLC) is often used to monitor the progress of an
organic reaction. For the following ester hydrolysis reaction, a solvent system is selected to give the
starting material an Rf value of about 0.5. (1) Provide in the box below the structure of the expected
product 7. (2) Fill in the spots that would be expected when the reaction is 50% compete and 100%
complete. Make sure to assign each spot you draw to the corresponding compound number (5, 6, or 7).
Consider only the compounds that can be visualized as a spot on TLC upon exposure of each solventdried plate to a 254 nm-UV lamp.
CH3
O
O
H2SO4 (cat)
H2O
Δ (heat)
5
O
OH
+
6
7
3
100% completion
50% completion
solvent
front
On each TLC plate, a student has placed
a sample of the starting material (5) as a
reference on the left of the plate, a spot
of the reaction mixture (after acidic workup) on the right, and a co-spot in the center
of each. Co-spotting is where some of 5
and some of the reaction mixture are
spotted together in order to make better
comparisons.
5 co-spot
reaction mixture
5 co-spot
reaction mixture
216 S10-Exam #1 Page 3.
Name ______________________
III. (17 points) N-Benzylaniline can be prepared by reaction of benzyl chloride and aniline in the presence
of aqueous sodium bicarbonate (NaHCO3).
Cl
benzyl chloride
NH2
+
+
NaHCO3
aniline
N
H
+
NaCl +
H2O + CO2
N-benzylaniline
The procedure calls for 372 g of aniline, 127 g of benzyl chloride, and 105 g of sodium bicarbonate
dissolved in 100 mL of water, and produces 160 g of N-benzylaniline.
Write an answer in the box provided to each of the following questions.
(1) (3 points) Calculate as to how many moles of each of the reagents are used in this procedure. Use the
following atomic weights: C = 12, H = 1, N = 14, O = 16, Na = 23, Cl = 35.5
benzyl chloride: _______ moles; aniline: _______ moles; NaHCO3: ________ moles
(2) (2 points) What is the limiting reagent?
(3) (3 points) What is the theoretical yield of N-benzylaniline?
______________ g
(4) (2 points) What is the percentage yield of N-benzylaniline?
______________ %
(5) (2 points) About 260 g of aniline can be recovered from the reaction. Does this affect the calculation
of theoretical yield? Explain.
(6) (2 points) What volume of benzyl chloride (density 1.10 g/mL) is required for the reaction?
________________ mL
(7) (3 points) Why is it necessary to use such a large excess of aniline for the reaction? Explain.
216 S10-Exam #1 Page 4.
Name_________________________
IV. (18 points) For each of the following reactions, provide in the box below a step-by-step mechanism
through the use of the curved-arrow convention.
O
(1)
OH
O
H3O+ workup
NaBH4
CH3
O
O
CH3
O
O
ethanol
(i.e., protonation)
O
O
H
H H
O
Mechanism including the H3O+ workup step:
O
O
O
CH3
O
O
H
H
H B H
H
Na
OH
O
O
O
(2)
O
OH
OH
H
H
TsOH*
O
7
O
O
TsOH* (catalytic)
benzene, reflux
4h
= H3C
(pKa = - 0.51)
Mechanism:
H H
CH3
O
S OH
H
+ H2O
H
O
H OTs
O
OH
OH
H
H
O
O
H
H
11
216 S10-Exam #1 Page 5.
Name _________________________
V. (6 points) For each of the following sets of compounds, match the expected IR frequencies for the
C=O bond stretching vibration to the wavenumbers given.
(1) 1694, 1686, or 1666 cm-1
O
O
O
O
H3CO
N
O
cm-1
cm-1
cm-1
(2) 1763, 1719, or 1687 cm-1
O
O
O
O
O
O
H2N
cm-1
cm-1
cm-1
VI. (3 points) A mixture of chlorobenzene (bp 132 °C) and water (bp 100 °C) could be steam distilled at
90 °C. The vapor pressure of water at 90 °C is measured to be 526 mmHg. What would be the vapor
pressure of chlorobenzene at 90 °C? Write your answer in the box below.
____________ mmHg
VII. (12 points) For each of the following synthetic reactions, draw the structure of the expected product
in the box provided.
(1)
NH2
O
+
H3C
HO
O
O
+
CH3
3
(2)
H3C
OH
H3C
HO
+
3
OH
O
(solvent)
+ H2O + NaCl
NaOCl
CH3
3
(3)
O
H3C
+
H2N OH
TsOH (catalytic)
+ H2O
H3C
3
216 S10 Exam #1 Page 6
Name________________________
VIII. (12 points). Given below are infrared (IR) spectra of four compounds. The compounds are among
those structures given on page 8. Assign each spectrum to its compound by putting the letter
corresponding to the compound in the answer box next to the spectrum. The tables of characteristic
infrared frequencies appear on pages 9 and 10.
(1) (liquid film) Answer
(2) (liquid film) Answer
216 S10 Exam #1 Page 7. VIII. (continued)
(3) (liquid film) Answer
(4) (KBr disc) Answer
Name _________________________
216 S10 Exam #1 Page 8
Name ________________________
VIII. (continued)
NH2
H
A
H3C
HO
H
N
OH
OH
B
CH3
I
O
J
C
N
CH3
CH3
CH3
CH3
H
O
D
H3C
OH
N
K
O
H3C
OH
H3C
E
N
L
O
N
H3C
F
CH3
G
O
H3C
O
O
CH3
M
H3 C
H3 C
H3 C
O
O
CH3