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CHEM 2010- Organic Chem 1
Quiz 1
Fall 2022
Name: _______________________
Multiple Choice format- choose the one best answer for each question. Note that for those
where the answers have roman numerals: I =A, II=B, III=C, IV=D, V=E
Mark your answers on the provided Scan-Tron form.
1. Which of the following structures have -1 as a formal charge on an oxygen atom?
2. What is the correct Lewis structure for the molecule shown in the box below?
3. Which of the following compounds are constitutional isomers of each other?
A.
B.
C.
D.
E.
I and II
II and III
III and IV
I and IV
II and III
4. Which of the following statements best describes the C—Cl bond in the following
compound?
A.
B.
C.
D.
E.
nonpolar; no dipole
polar; d+ at carbon and d– at chlorine
polar; d– at carbon and d+ at chlorine
polar; d– at carbon and d– at chlorine
ionic
CHEM 2010- Organic Chem 1
Quiz 1
Fall 2022
5. What is the hybridization of the indicated atoms in the following compound?
A.
B.
C.
D.
E.
I = sp ;
I = sp2 ;
I = sp3 ;
I = sp2 ;
I = sp2 ;
II = sp2 ;
II = sp ;
II = sp2 ;
II = sp3 ;
II = sp2 ;
III = sp3 ;
III = sp2 ;
III = sp ;
III = sp2 ;
III = sp2 ;
IV = sp2
IV = sp3
IV = sp2
IV = sp
IV = sp3
6. What is the molecular geometry at the nitrogen atom in the following compound?
A.
B.
C.
D.
E.
trigonal planar
trigonal pyramidal
linear
tetrahedral
bent
7. Rank the following compounds in order of decreasing dipole moment.
A.
B.
C.
D.
E.
I > II > III
II >III > I
I > III > II
III > I > II
II > I > III
CHEM 2010- Organic Chem 1
Quiz 1
Fall 2022
8. For the following chemical reaction, how many hydrogen atoms are added or lost?
A.
B.
C.
D.
E.
one hydrogen atom added
two hydrogen atoms added
one hydrogen atom lost
two hydrogen atoms lost
no change in the number of hydrogen atoms
9. Which of the following is the correct condensed structure for the following
compound?
A.
B.
C.
D.
E.
CH3CHCH3CH2OH
CH3CH2CH2OH
(CH3)2CHCH2OH
CH3CH2CH2OCH3
CH3CH3CHCH2OH
10.
Tamiflu®, the most effective antiviral drug used to treat avian influenza, has
the following structure. Identify the functional groups in Tamiflu®.
A.
B.
C.
D.
E.
I = ester;
I = ether;
I = ether;
I = alcohol;
I = ether;
11.
A.
B.
C.
D.
E.
one
two
three
four
none
II = aromatic;
II = aromatic;
II = alkene;
II = alkyne;
II = alkene;
III = carboxylic acid
III = anhydride
III = ether
III = carboxylic acid
III = ester
How many lone pairs of electrons are found on the indicated atom?
CHEM 2010- Organic Chem 1
Quiz 1
Fall 2022
12.
Identify bond-line structures for constitutional isomers with a molecular
formula of C3H8O.
A.
B.
C.
D.
E.
I and II
I and III
II, IV, and V
II and IV
I and IV
13.
For the following compound identify the indicated lone pairs as localized or
delocalized.
A.
B.
C.
D.
E.
I = both delocalized;
I = both localized;
I = both delocalized;
I = one localized and one delocalized;
I = one localized and one delocalized;
II = localized
II = localized
II = delocalized
II = localized
II = delocalized
14.
Caffeine has the following structure. Identify the hybridization and molecular
geometry at the indicated atoms.
A.
B.
C.
D.
E.
I = sp3, trigonal pyramidal;
I = sp3, trigonal planar;
I = sp2, trigonal pyramidal;
I = sp2, trigonal planar;
I = sp3, trigonal pyramidal;
II = sp2, trigonal planar
II = sp2, bent
II = sp, linear
II = sp2, bent
II = sp2, bent
CHEM 2010- Organic Chem 1
Quiz 1
Fall 2022
15.
Identify the structure that shows the correct placement of all lone pairs for
the compound illustrated in the box below.
16.
Which of the following violates the rules for curved arrows?
17.
Identify the proper curved arrows to convert the first resonance structure
into the second resonance structure.
18.
For the structure shown in the box below, identify corresponding correct
resonance structures.
A.
B.
C.
D.
E.
I and II
II and III
III and IV
I, II and III
II, III and IV
CHEM 2010- Organic Chem 1
A.
B.
C.
D.
E.
Quiz 1
19.
Identify the most significant resonance structure(s).
20.
What is the relationship between the following structures?
Fall 2022
constitutional isomers
resonance structures
conformers
identical compounds
stereoisomers
21.
Identify the resonance hybrid for CH2=CHCH=CHCH2+.
22.
Identify the conjugate base of CH3C≡CH.
23.
Identify the structure produced by the following acid-base reaction
mechanism (and electron delocalization).
CHEM 2010- Organic Chem 1
Quiz 1
Fall 2022
24.
For the following acid-base reaction, predict the position of the equilibrium
and identify the most acidic compound.
A.
B.
C.
D.
E.
favor the right side with compound I being the most acidic compound
favor the right side with compound III being the most acidic compound
favor the left side with compound I being the most acidic compound
favor the left side with compound III being the most acidic compound
The reaction is at equilibrium so all the compounds are in equal concentration
25.
Which of the following best explains if H2O is a suitable reagent to protonate
the compound shown below.
A.
B.
C.
D.
E.
no, water would not protonate the compound as the resulting conjugate base would
not be stabilized by resonance
no, water would not protonate the compound as the negative charge is more stable
on the nitrogen atom
no, water would not protonate the compound as both water and the nitrogen in the
compound have two bonds
yes, water would protonate the compound as the resulting conjugate base would
be stabilized by resonance
yes, water would protonate the compound as the resulting conjugate base would
have a negative on the more electronegative oxygen atom
CHEM 2020
Test 1
Name:_
ama
Fall 2020
KEY
For each Question below, mark your answer on this document and input you answer into eLearn.
Some questions will ask for you to show work or to explain your reasoning on this test document.
Note: eLearn will mark the MC portion as correct or incorrect, however, the instructor has the
me
option to deduct points if the proper work/logic is not provided to support your answer.
25 3pts
75pts 1. Which of the following compounds are constitutional isomers of each other?
email students if
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A.
B.
C.
D.
E.
I and II
III and IV
I, II and IV
II, III and IV
I, II, and III
2. What is the correct Lewis structure for CH3CO2H?
H
H
H
C
C
H
O
O
H
O
C
C
H
I
C
H
H
I
A
H
A.
H
C
O
O
H
C
O
H
C
C.
C
O
O
O
C
H
III
co
H
H
II
H
H
H
II
B
IV
B.
H
O
H
V
OE
III
D.
IV
E.
V
1
CHEM 2020
Test 1
Fall 2020
3. Which of the following structures have a +2 formal charge on the sulfur atom?
H
H C S
H
H C S C H
H
I
A.
R
I
H
H
S
O
O
O
H C S H
H
H O S O H
O
H
II
B.
H
IV
III
I
II
I
C.
III
D.
Am
IV
V
E.
V
an
4. What is the correct Lewis structure for nitric acid, HNO3, including the formal charges?
1A
N 5
30
24e
X
A. I
H I
x
B. II
B
C
µ
C. III
D. IV
µ
D
E. None of these
0oz
5. Which of the following statements best describes the C—Cl bond in the following
compound?
H
f
A.
B.
C.
D.
E.
H
Cl
C
H
C
r C
H
H H H
nonpolar; no dipole
polar; d- at carbon and d+ at chlorine
polar; d+ at carbon and d- at chlorine
ionic
None of these.
6. The C2—C3 bond in the following compound results from the overlap of which orbitals?
H
H
C
H
A.
B.
C.
D.
E.
sp–sp2
sp–sp3
sp2–sp2
sp2–sp3
sp3–sp2
O
C
3 C
H
C 23
2 C
H H H H
Sp sp
2
CHEM 2020
Test 1
Fall 2020
7. The C to C triple bond indicated by the arrow in the following compound results from the
overlap of which orbitals?
G
C C
H
H
A.
B.
C.
D.
E.
2
H
C
C
C
H
H
H
0
2
one sigma bond sp – sp , one pi bond sp –sp
two sigma bond sp – sp, one pi bond p – p
one sigma bond sp2 – sp2, two pi bond sp2 – sp2
one sigma bond sp – sp, two pi bonds p – p
one sigma bond sp3 – sp3, two pi bond p – p
sp sp
Z x
p p
8. Consider the relative bond length and relative bond strength for the following
compounds.
H
C
C
H
H
mmmm
I
A.
B.
C.
D.
E.
H
H
I
C mC
H
II
the shortest and strongest bond is found in compound I
the shortest and strongest bond is found in compound II
the shortest and weakest bond is found in compound I
the shortest and weakest bond is found in compound II
the bonds are of identical length and strength
9. Provide a complete Lewis dot structure for methyl anion, CH3-1 .
Redraw with the appropriate molecular geometry.
Use this structure to determine the hybridization state, molecular geometry, and
approximate H-C-H bond angle.
A.
B.
C.
D.
E.
NOwork
partial
A
sp2, tetrahedral, 1090
sp3, tetrahedral, 109.50
sp2, trigonal planar, 1200
sp2, trigonal pyramidal, 1800
sp3, trigonal pyramidal, 1200
21
CHI
se
H
id H
I
it
4mg
sp’s
trig pyr
H
H
It
10999.55
3
CHEM 2020
NOwork
partial A.
B.
C.
I D.
E.
Test 1
Fall 2020
Zpts
10. Provide a complete Lewis dot structure for methyl cation, CH3+1 .
Redraw with the appropriate molecular geometry.
Use this structure to determine the hybridization state, molecular geometry, and
approximate H-C-H bond angle.
2
H 3mg Sp
alto
trig planar
CH
be
0
sp , tetrahedral, 109
sp3, trigonal pyramidal, I > IV > II
II > IV > I > III
III > I > II > IV
IV > II > I > III
I > III > II > IV
l
Hae
I
affined
night
lowest
14. For the following equation, how many hydrogen atoms are added or lost?
i
A.
B.
C.
D.
E.
added one
added two
lost one
lost two
no change
y
k
f
s
l OH
tout
isH
s
k
l
IT
MH
15. What functional group(s) is (are) present in the following compound?
O
A.
B.
C.
D.
E.
ketone and alkene
ketone and alkyne
aldehyde and alkene
aldehyde and alkyne
ester and alkene
5
CHEM 2020
Test 1
Fall 2020
16. Which of the following compounds have -1 as a formal charge on the nitrogen atom?
O
A.
B.
C.
D.
E.
N
NI
0
O
II
I
I
0
N
N
III
I
II
III
IV
Both I and II
1I
IV
17. How many total lone pairs of electrons are in the following compound?
anime
A.
B.
C.
D.
E.
two
three
four
five
six
18.
I
Which of the following violates the rules for curved arrows?
t
uma
N
I
A.
B.
C.
D.
E.
I and II
III and IV
I, and III
II, III and IV
all of these
19.
X
raO
MakeO
II
if
IIII
x
ok
da
IV
ok
Which of the following is/are correct resonance structure(s) for compound A?
A
N
6
CHEM 2020
A.
B.
C.
D.
E.
Test 1
Fall 2020
r
o
i
e
I and II N
II and III
III and IV
I and III
I and IV
E
N
20.
Which of the following is a correct resonance structure for the compound shown
below?
i
N
A
A
B
21.
C
D
Ekta
Which of the following is the most significant resonance structure?
u
H2C
Q
N
I
N
H2C
A.
be
N
II
N
B
B.
one
EgD.
EsC.
onN
ke
Be
7
CHEM 2020
22.
Test 1
Fall 2020
The lone pairs on oxygen in the following compound are _______.
i
A.
B.
C.
both localized
both delocalized
one localized and one delocalized
23.
high
low
Rank the indicated protons in increasing order of acidity.
O ddocalizedonto
I H
OC E
chary
high
Mac
mid
whoork
0
A.
B.
III H
3C
II > I > III
II > III > I
I > III > II
I > II > III a listed hightoloqo.net
inoorder
III q
> II q
>I
24.
Yes
No
more
acidic
II
H
A.
B.
C.
D.
E.
stable 4g
2C
low
high
few
LI
KI
Determine if NaOH is a suitable reagent to deprotonate the following compound.
R
c
Q
H
Ht
O
t
R
H2O
C sp
msofabilized
25.
Which of the indicated carbons is bonded to the most acidic proton?
I
IV
H H
H
H CH H C
H
info
C
H
C
C
H
H
III
II
allylic
resonance
delocalized
8
CHEM 2020
Test 1
Fall 2020
amo
2Epts Part 2: Free Response- Answer all questions completely.
total
ster
26.Consider each of the incomplete structures below.
Naphthalene
µ
Aspirin
space
Olde
Hz
Arene
Arene
acid
car sylic
Aromatic
Nicotine
3C
Tyrian purple dye
Ami
gp2 sP
o
I
Br
googiodff
Nsfsd
N
sp2 sp3
H
Nd
ao
Atone
CHs
Il
a
N
o
L
O
Allspace
elecpairsore
all N all
I
A
delocalized
t’s
Br
ah
a. Complete all structures
any to clearly show all non-bonding pairs of electrons.
b. Which molecule(s) has only sp2 hybridized carbon atoms?
_____________________________________________________________
purple
naphthalene
Tyrian
a
dye
c. Which of the structure(s) has no delocalized non-bonding electron pairs on a nitrogen
atom? _______________________________________________________
nicotine
cc
nicotine
d. Which molecule(s) contains on sp2 hybridized nitrogen atoms?
she’d
9am.gg
_____________________________________________________________
p
My
nine
e. Neatly circle and name at least four different functional groups within this group of
molecules.
Arena
ester
carboxylicacid
amino
ketone
alkylhalide
9
CHEM 2020
Test 1
Fall 2020
27. Could the compound below be deprotonated by NaNH2?
H
Nu
H
a. Provide structures and appropriate curved arrow notation to illustrate this acid
base reaction that could occur.
b. Give a brief explanation for your prediction of the reaction’s success or failure
3
3
Nato
O
I
Nor
0
iVHz
H
O
Tha
f
IT
H
0
charged
J
resonance
stabilized
many
overnNO
a
I
O
delocalized
charge
Mesto
NHz
t
µ
H
28. Consider the cation below.
a. Provide all key resonance structures of the ion.
V
3 V
l
b. Identify
the resonance structure you expect to contribute most strongly to the
3
choice 2
resonance hybrid. Explain
your
c. Include curved arrow notation
to illustrate how each resonance structure could shift
z
electrons to generate the next.
H
H
l
H
I
s
Ml
I
H
a00
I GRO
H
l
oo
H
major
Allatonishau chashei
Chastee
an octet
Contributor
10
1
IA
1
18
VIIIA
H
1
Hydrogen
3
Li
2
C
7
N
16
VIA
8
O
17
VIIA
9
F
12.01
14.01
16.00
19.00
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
12
13
Na Mg
22.99
24.31
Sodium
Magnesium
20
3
IIIB
21
4
IVB
22
5
VB
23
6
VIB
7
VIIB
25
8
┌
9
VIIIB
27
24
26
10
┐
28
11
IB
29
12
IIB
30
Al
14
Si
15
P
16
S
17
Cl
He
4.00
Helium
10
Ne
20.18
Neon
18
Ar
26.98
28.09
30.97
32.07
35.45
39.95
Aluminum
Silicon
Phosphorus
Sulfur
Chlorine
Argon
31
32
33
34
35
36
K
Ca
Sc
Ti
V
Cr
Mn Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
39.10
40.08
44.96
47.87
50.94
52.00
54.94
58.93
58.69
63.55
65.39
69.72
72.61
74.92
78.96
79.90
83.80
Potassium
37
Rb
85.47
Rubidium
55
Calcium
38
Sr
87.62
Strontium
56
Scandium
39
Y
88.91
Yttrium
57
Titanium
40
Zr
91.22
Zirconium
72
Vanadium
41
Chromium
42
Manganese
43
Nb Mo Tc
92.91
Niobium
73
95.94
[98]
55.85
Iron
44
Ru
101.07
Molybdenum
Technetium
Ruthenium
74
75
76
Cobalt
45
Rh
102.91
Rhodium
77
Nickel
46
Pd
106.42
Palladium
78
Copper
47
Ag
107.87
Silver
79
Zinc
48
Cd
112.41
Cadmium
80
Gallium
49
In
114.82
Indium
81
Germanium
50
Sn
118.71
Tin
82
Arsenic
51
Sb
121.76
Antimony
83
Selenium
52
Te
127.60
Tellurium
84
Bromine
53
I
126.90
Iodine
85
Krypton
54
Xe
131.29
Xenon
86
Cs
Ba
La
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
132.91
137.33
138.91
178.49
180.95
183.84
186.21
190.23
192.22
195.08
196.97
200.59
204.38
207.2
208.98
[209]
[210]
[222]
Cesium
87
7
B
6
15
VA
10.81
19
6
Be
5
14
IVA
9.01
4
5
4
13
IIIA
6.94
11
3
Periodic Table
of the Elements
2
IIA
1.01
2
Fr
[223]
Francium
Barium
88
Ra
[226]
Radium
Lanthanum
89
Ac
[227]
Actinium
Hafnium
104
Rf
[267]
Rutherfordium
Tantulum
105
Db
[268]
Dubnium
58
Ce
140.12
Cerium
90
Tungsten
106
Sg
[271]
Seaborgium
59
Pr
140.91
Rhenium
107
Bh
[272]
Bohrium
60
Osmium
108
Hs
[270]
Hassium
61
Iridium
109
Mt
[276]
[145]
Praseodynium
Neodymium
Promethium
91
92
93
110
Ds
[281]
Gold
111
Rg
[280]
Mercury
112
Thallium
113
Lead
114
Bismuth
115
Polonium
116
Astatine
117
Radon
118
Cp Uut Uuq Uup Uuh Uus Uuo
[285]
[284]
[289]
[288]
[292]
[292]
[293]
Meitnerium
Darmstadtium Roentgenium
Copernicium Ununtrium
Ununquadium Ununpentium Ununhexium
Ununseptium
Ununoctium
62
63
65
67
70
71
Nd Pm Sm
144.24
Platinum
150.36
Samarium
94
Eu
151.96
Europium
95
64
Gd
157.25
Gadolinium
96
Tb
157.93
Terbium
97
66
Dy
162.50
Dysprosium
98
Ho
164.93
Holmium
99
68
Er
167.26
Erbium
100
69
Tm
168.93
Thulium
101
Yb
173.04
Ytterbium
102
Lu
174.97
Lutetium
103
Th
Pa
U
Np
Pu Am Cm Bk
Cf
Es
Fm Md No
Lr
232.04
231.04
238.03
[237]
[244]
[251]
[252]
[257]
[262]
Thorium
Protactinium
Uranium
Neptunium
Plutonium
[243]
Americium
[247]
Curium
[247]
Berkelium
Californium
Einsteinium
Fermium
[258]
Mendelevium
[259]
Nobelium
Lawrencium
Chemistry 2010: Organic I
Laboratory
Investigating Gas Chromatography
Gas Chromatography is a technique widely used to separate complex mixtures of substances.
Compounds present in a volatile liquid or gaseous solute are isolated after traveling through a
coated column based on the substance’s size and intermolecular interactions. If a compound
tends to bind to the column through intermolecular interactions, it takes a longer time to emerge
compared with a compound that does not tend to stick onto the column. The level of binding
experienced between the substances and the column is determined based on the number and
strength of intermolecular interactions between the two species. Substances that pass quickly
through the column exhibit fewer intermolecular interactions with the column.
The Vernier Mini GC uses a metal column with a nonpolar coating, called the stationary phase.
A sample, consisting of one or more compounds, is injected into the column and is carried
through the stationary phase by atmospheric air, which acts as the mobile phase. The nonpolar
coating of the stationary phase most strongly retains solutes of the same polarity. Organic
compounds flowing out of the chromatography column are then detected by a chemical sensor
that produces electrical responses proportional to the concentration of the compounds. The
presence of such a chemical at the detector is seen as a peak on a chromatogram, as shown in
Figure 1. The unique time it takes for a compound to exit the column after it is injected is called
the retention time. With a gas chromatograph, a compound can be identified from a mixture by
its retention time.
Figure 1 Sample gas chromatogram
Several factors can affect a compound’s retention time. More volatile compounds
(i.e., compounds with a lower boiling point) will move through the column faster because they
are flowing in the mobile phase and not strongly bonded with the stationary phase. The surface
functional groups present on the compound are also a factor. For example, alcohols may weakly
bond with a polar stationary phase more than esters because alcohols are capable of forming
hydrogen bonds. The molecular weight of a compound may also play a role to a slight extent,
although it is not a direct relationship that the heavier the molecule, the slower it will travel
through a GC column.
As you will discover in this experiment, the instrument settings also affect a compound’s
retention time. When separating compounds with a wide range of boiling points and polarities, it
helps to raise the column temperature during the separation. Temperature programming reduces
elution times of highly retained compounds. Adjusting the pressure will have a similar affect;
Adapted from Organic Chemistry wth Vernier
1
Investigating Gas Chromatography
higher pressures cause greater strain on the intermolecular interactions between the compound
and stationary phase, ultimately reducing the retention time.
In this experiment, you will gain experience with the Vernier Mini GC by injecting a known
sample into the device. The sample contains four compounds that will separate under the proper
conditions. You will test this one mixture of compounds repeatedly and vary the profile of the
Mini GC operation to obtain the best possible separation of this mixture.
OBJECTIVES
In this experiment, you will
• Measure and analyze the chromatogram of a mixture of four compounds as they pass
through a Vernier Mini GC.
• Vary the temperature-pressure profile of the Mini GC and observe how the chromatogram
is affected by such changes.
• Determine the best temperature-pressure profile to obtain clear separation of all four
compounds.
PRE-LAB QUESTIONS
WATCH Video 1: Gas chromatography | Chemical processes | MCAT | Khan Academy to
answer the questions below.
1. Sketch a basic model of a gas chromatograph instrument and label the parts.
2. For GC, the mobile phase is the __________ and the stationary phase is the __________.
3.
What is the resulting graph produced called? _________________________
4. What are two major factors that affect how long it takes a compound to reach the
detector?
5. The graph generated ( aka:___________) is a plot of _________ vs __________.
6. What property is ideal for a solvent to be used during a GC study?___________
7. Note that the area under the peak is directly proportional to
_______________________________________________________________.
8. Considering the answer to number seven, what would you approximate the relative
proportion to be between A and B in this example?
2
Thin-Layer Chromatography:
Identifying an Unknown Analgesic
PART 1: PRE LAB READING AND RESEARCH
THEORY
Refer to the links below for background information. Take notes on each reference.
Chromatography Generalities
Overview of Chromatography
General Separation Theory
Thin Layer Chromatography (TLC)- Theory and Technique- Professor Dave Explains video
Thin Layer Chromatography (TLC) Parts A-F
In this experiment, TLC will be used to identify the active ingredients in an unknown overthe-counter medicine tablet. The tablet you will test contains one or more of the following:
acetylsalicylic acid (aspirin), acetaminophen (the active ingredient in Tylenol®), caffeine, and/or
ibuprofen (the active ingredient in Advil®). The structures of these compounds are shown in
Figure 1.
Acetylsalicylic acid
(aspirin)
Acetaminophen
Caffeine
Ibuprofen
Figure 1. Structures of analgesics
Thin-layer chromatography (TLC) is an important technique in organic chemistry. TLC uses
the different affinities a compound has for a mobile phase and a stationary phase to achieve
separation of mixtures of organic compounds. TLC can also be used to identify compounds by
comparison with known samples, check the relative purity of a compound, and monitor the
progress of a reaction.
In thin-layer chromatography, the stationary phase is the adsorbent (usually silica or alumina)
coated on a sheet of glass, metal, or plastic. The sample is applied as a spot near the bottom of
Adapted from: Organic Chemistry with Vernier
CHEM 2010 LAB
TLC
the plate. The TLC plate is then placed in a developing chamber containing a shallow layer of
solvent where the mobile phase (solvent) slowly rises by capillary action.
Under a given set of conditions, a specific compound will travel a fixed distance relative to the
solvent front. Different compounds generally move at different rates. As a result, if the sample is
a mixture of compounds it will separate into a series of spots at varying distances up the plate
(see Figure 2). If the sample is pure, then only one spot will result. A UV light source is used to
visualize the spots on the TLC plate. Under UV light, the chemical deposits will appear as dark
spots against a bright background.
TLC separation results are expressed in terms of Rf (retention factor) values. The Rf is a ratio
calculated by dividing the distance traveled by the sample by the distance traveled by the solvent
at the end of the experiment.
Figure 2. Example TLC plate at the end of the experiment
Clean spots are achieved if a small amount of each sample is applied to the plate at reasonable
distances for the edges and each other. If the spot has too much compound loaded onto it,
streaking/tailing will occur (Figure 3). If spots are too close to each other or to the edge
smearing or veering off will occur.
Figure 3. Example of streaking/tailing seen with overloading a spot
Adapted from Organic Chemistry with Vernier
2
CHEM 2010 LAB
TLC
A “spot” of compound or reaction is deposited on the plate near the bottom as shown. The plate
is placed in a container that has a small amount of solvent just covering the bottom. The solvent
quickly begins diffusing up the plate. As the solvent diffuses upward, the spot travels if it is
soluble in the solvent. The rate and distance the spot travels depend on its polarity and the
presence of functional groups that can participate in hydrogen bonding. In general, more polar
compounds stick to the silica tightly and move slower. Less polar compounds stick to the silica
less and will travel higher up the plate.
PRE-LAB QUESTIONS
1. How would you change your technique for application or solvent system if each of these
issues was observed:
a. Large spot that trails up plate
b. Barely visible spot
c. Spot barely moves even with solvent near top of plate
d. Both compounds of mixture travel with solvent front to top with little to no
separation.
2. The unknown you will test today will be Tylenol®, Excedrin®, Aleve, or Advil®. Do some
research to determine the active ingredients in each of these. You are interested in
the compounds listed in Figure 1.
Adapted from Organic Chemistry with Vernier
3
CHEM 2010 LAB
TLC
PART 2: Begin Lab Session With A Technique Review
Ø Watch technique video Thin Layer Chromatography (TLC)- Theory and TechniqueProfessor Dave Explains video (This is the same video you watched in Pre-lab
assignment. Review your notes and/or the video to answer questions below with your
group.)
1. What is the main factor that the separation of compounds is based on?
2. What are some contributing factors?
3. Compounds interact with the mobile phase during TLC. Do they interact with the
stationary phase? Explain.
4. Why is a pencil used to mark the TLC plate?
5. Why is it important to not press the capillary tube to not disrupt the silica on the plate?
6. Why should the spot on the plate sit above the level of the solvent? Wouldn’t it dissolve
better if it was in the solvent?
7. Is it possible to have an Rf greater than 1? Why?
Adapted from Organic Chemistry with Vernier
4
CHEM 2010 LAB
TLC
PART 3: Observe/Perform The Experiment
OBJECTIVES
In this experiment, you will
• Use TLC results to determine optimal solvent system for efficient resolution of spots in a
mixture.
• Calculate the Rf values of acetylsalicylic acid, acetaminophen, caffeine, and ibuprofen.
• Use TLC to identify your unknown analgesic as Tylenol®, Excedrin®, Aleve, or Advil®.
READING
Refer to your Pre-lab notes, particularly those on Thin Layer Chromatography (TLC) Parts A-F,
to better understand the experimental procedure and to address the post-lab questions.
MATERIALS
Thin-Layer Chromatography
acetaminophen in ethyl acetate
acetylsalicylic acid in ethyl acetate
caffeine in ethyl acetate
ibuprofen in ethyl acetate
three TLC plates (5 ´ 10 cm)
three 400 mL beakers
three 9 cm watch glasses
cotton plug
disposable Pasteur pipets and bulb
pencil
ruler
10 mL graduated cylinder
UV lamp (shortwave)
ethyl acetate
n-hexane
spotting capillary tubes
five 10 ´ 75 mm test tubes
test tube rack
unknown sample
mortar and pestle
filter paper
SAFETY: Obtain and wear goggles. Protect your hands by wearing gloves. Conduct this
procedure in a fume hood; keep all chambers covered as much as possible.
EXPERIMENTAL PROCEDURE:
Watch the experiment video Organic Chem lab: Lab Techniques- Thin layer Chromatography.
While you are watching, follow along with the procedural steps provided below. Pay attention,
assure that you understand why the wording and what you observe correlate. To illustrate that
you paid attention to the video, give time stamps in the left margin for all major steps
observed.
1. Prepare the TLC plates.
a. Obtain two TLC plates and label in top corner to indicate the solvent used. It
should be either EA or H for the first plate you run then Mix for the second.
Handle them carefully and by the edges or top so that the adsorbent does not flake
off and you do not contaminate the surface with oils from your skin or gloves.
Adapted from Organic Chemistry with Vernier
5
CHEM 2010 LAB
TLC
b. Using a blunt-tip pencil (NOT an ink pen), lightly draw a line across the plate,
approximately 1 cm from the bottom. Careful not to scratch the plate surface!
Across this line, evenly mark five places indicating the location where the sample
will be spotted, making sure they are not too close to the edge of the plate or each
other (see Figure 2). Do this for both TLC plates.
c. Above each mark, at the top of the plate, lightly label each spot starting left to
right as Ac, As, C, I, and U. Lay the plates on a paper towel in front of your hood.
d. Obtain a drawn capillary tube ‘spotter’ from your instructor. Dip one end of the
‘spotter’ into the ethyl acetate solution containing acetaminophen. Capillary action
will draw the liquid into the tube.
e. Lightly, and quickly, touch the tube on the mark for acetaminophen on both TLC
plates. Only a small amount of sample needs to be delivered. The spot should be
1-2 mm in diameter.
f. It is imperative that you CLEAN your spotter between sample types with a few
washes of pure ethyl acetate!! Get a clean paper towel and lay it out beside your
plate. Touch the used spotter to the paper towel to draw any remaining solution
out. Dip the tip of the spotter into the ethyl acetate vial to draw up solvent then
draw that out by touching to the paper towel again. Repeat a few times to assure
the spotter is clean.
g. Repeat Steps e-g for aspirin, caffeine, ibuprofen, and the unknown sample on both
of your TLC plates. Again, CLEAN your spotter between sample types!
2. Prepare the TLC chamber. You will work with your bench-mate to complete all the
data collection needed for this analysis. One partner will run a plate in pure ethyl acetate,
and the other will run a plate in pure hexane.
a. Label the chambers by the solvent system to be used.
b. Place a piece of filter paper (folded at ¼ of diameter) against the side of the
beaker, flat edge down. The filter paper will help saturate the beaker with solvent
vapors.
c. Saturate the filter paper with the solvent but do not let more than 1/2cm of solvent
collect in the bottom. If it does use a pipette to remove some. Cover the
chamber with lid/watchglass and place under your student hood.
Adapted from Organic Chemistry with Vernier
6
CHEM 2010 LAB
TLC
3. Develop the TLC plates.
a. The solvent level must not be above the spots on the plate or your samples will
dissolve into the solvent. Check this by holding your plate up next to the
outside the chamber. Use a long stem pipette to add or remove solvent until
you are confident it will wet the plate but not get near the spots.
b. Handling by the top edge, place one of the TLC plates in the chamber with the
pure solvent, carefully, and cover with the watch glass.
c. Once the plate touches the solvent do not pick it up or move the chamber. The
solvent needs to rise evenly.
d. When the solvent has risen to within 1 cm from the top of the plate, remove the
plate from the chamber and immediately use a pencil to gently draw a line to
mark the position of the final solvent front.
4. Analyze the TLC plates developed in pure solvents.
a. After the plate has dried, observe the TLC plate under a UV lamp. Lightly outline
the spots with the pencil. CAUTION: Do not allow skin or eyes to come in
contact with UV light. Wear gloves, a lab coat, and UV resistant eye protection.
b. Observe the two plates developed by you and your partner. [See the Inserted
images in the results section below.]
Adapted from Organic Chemistry with Vernier
7
CHEM 2010 LAB
TLC
PART 4: RESULTS AND ANALYSIS
1. Results for plates developed in pure solvents:
Ethyl acetate
Hexane
2. Evaluate the results from your solvent mixture development
a. Identify the solvent system that gave the best separation. Use the image of this
TLC plate (above) to mark and label all pertinent measurements involved in
the calculation of the Rf values. (Measure the plate itself then write down the
measurements on the image.)
b. Calculate the Rf value for each spot. Record the results in the data table.
Sample
Distance traveled by
solvent (cm)
Distance traveled by
spot (cm)
Rf value for each spot
Acetaminophen
Aspirin
Caffeine
Ibuprofen
Unknown
3. Based on your Rf value(s) for the unknown mixture, identify your unknown analgesic as
Tylenol®, Excedrin®, Aleve, or Advil®. Explain your logic.
Adapted from Organic Chemistry with Vernier
8
CHEM 2010 LAB
TLC
4. Consider the order of elution seen in your results. Explain why these compounds travel
up the plate in the relative order that they do.
5. Refer to Separation Theory. Scroll down to the Structural Consideration section.
Logically explain why there is a difference between the TLC in this section, shown below
and the TLC from our experiment. What is the difference between the two orders of
elution? Explain why this occurs.
Adapted from Organic Chemistry with Vernier
9
CHEM 2010 LAB
TLC
6. Look up the structure of Phenacetin, a pain and fever reducing drug withdrawn from
medical use after being classified as dangerous. Considering its structure, where would
you expect it to appear on the TLC plate had it been developed with pure Ethyl acetate as
the solvent. Explain your logic for the location.
7. If the solvent mixtures below were used, predict how these would affect the results of the
experiment. Sketch each TLC and discuss the logic behind your predictions.
Mixture 1= 1:1 Hexanes : Ethyl acetate
Adapted from Organic Chemistry with Vernier
Mixture 2= 2:1 Hexanes : Ethyl acetate
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