Experiment 56: Synthesis of
an Ester from an Alcohol
and Carboxylic Acid
Structure determination by
Infrared Spectroscopy
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Infrared Spectroscopy
• Read Chapter 25, pp 833 to 867
• Work problems on page 866-867
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Typical Infrared Absorption
Regions
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O-H stretch
• The OH peak is very strong and broad!
• It usually appears near 3400 cm-1
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C-H stretch
• sp3 C-H stretch comes at 2950 cm-1
• sp2 C-H stretch comes at 3050 cm-1
• sp C-H stretch comes at 3300 cm-1
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C=C stretch
• C=C stretch occurs near 1650 cm-1
• It is often weak unless it is conjugated
to a C=O
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Normal Base Values for
C=O Stretching
Functional Group
Frequency (cm-1)
Ester
Aldehyde
Ketone
Carboxylic acid
Amide
1735 - 1740
1725
1715
1710
1690
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C-O stretch
• The C-O band appears in the range of
1300 to 1000 cm-1
• Look for one or more strong bands
appearing in this range!
• Ethers, alcohols, esters and carboxylic
acids have C-O bands
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C-H bendings
• Bendings aren’t as important as
stretches.
• See page 848-850
• CH2 bending: 1450 cm-1
• CH3 bending: 1375 cm-1
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Cyclohexanol
O-H
stretch
sp3 C-H stretch
OH
bending
C-O
stretch
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Ethyl Butanoate
sp3
C-O stretch
C-H
O
C=O stretch
C
CH3 CH2 CH2
O
CH2 CH3
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4-Methyl-2-pentanone
C-H < 3000, C=O @ 1715 cm-1
CH3
C-H stretch
C=O stretch
O
CH3 CH CH2 C
CH3
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4-Methyl-3-penten-2-one
C-H stretch
O
CH3
C
CH3
C
C
H
CH3
C=O C=C
stretch stretch
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Experiment 15
Spearmint and Caraway
•
•
•
•
Experiment 15, pp124-131
Essay: pp119-123
Technique 25 (Infrared spectroscopy)
Technique 22 (Gas Chromatography,
especially, Section 22.8 on page 806
and Fig 22.7)
• Technique 23 (Polarimetry)
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Spearmint and Caraway Oils
O
O
H
H
(S) + carvone
Caraway oil
(R) - carvone
Spearmint oil
Limonene is present
In both oils
H
(S) - Limonene
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The experiment
• Run the IR spectrum on the two
enantiomers
• Run a sample of each enantiomer
through the gas chromatograph
• Determine the optical rotations for
each enantiomer
• Calculate the specific rotation for each
enantiomer
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Experiment 21
Nucleophilic Substitution:
Competing Nucleophiles
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Reading Assignment
•
•
•
•
•
•
•
pp. 180-190 (Exp 21) and 510-514 (exp 58)
Chapter 10 in your lecture textbook
Review Techniques 1 through 6
Technique 7 (Sections 7.2, 7.4, 7.5, 7.8)
Technique 12 (Sections 12.5, 12.9, 12.11)
Technique 22
Technique 21 (omit this quarter)
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Changes to Exp 19 laboratory
• We will be using 1-pentanol,
2-pentanol, 3-pentanol and 2-methyl-2butanol instead of what is shown in the
book.
• The procedure stays the same; just
change the alcohols.
• Start 21A first, then do 21B, and then
come back to finish 21A.
• Part 21C: gas chromatography only
• Signup for 1, 2, and 3-pentanol
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The SN2 Mechanism
H
.. _
O:
..
H
H
C
H
Br
H

O
H
C
H
H

Br
..
O
..
H
H
C
H
H
+
.. _
: Br :
..
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The SN1 Mechanism
1)
CH3
CH3 C
CH3
CH3
slow
CH3 C
+
: Br:
..
CH3
.. _
: Br :
..
+
carbocation
2)
CH3
CH3 C
+
H
CH3
+ :O:
CH3
fast
CH3 C
H
:O
CH3
+
H
H
3)
CH3
CH3
CH3 C
:O
H
CH3
+
H
fast
CH3 C
:O
..
CH3
+
H
+
H
1935: Hughes & Ingold
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Assisted SN2: Mechanism
1)
R
CH2 O
H + H
R
CH2 O
H
H
2)
slow
X
+
R
CH2
O
H
H
X
CH2
R
+
O
H
H
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Assisted SN1: Mechanism
1)
CH3
CH3
CH3 C
CH2 CH3
+ H
CH3 C
O
O
H
H
CH2 CH3
H
2)
CH3
CH3
slow
CH3 C
O
3)
CH2 CH3
CH3 C
CH2 CH3
H
+
O
H
H
H
CH3
CH3
CH3 C
CH2 CH3
+
X
CH3 C
CH2 CH3
X
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RBr/RCl
ROH
H2SO4
NH4Br/NH4Cl
H2O
organic
phase
pentane
aqueous
phase
pentane
RBr/RCl
ROH
H2SO4 (trace)
H2O (trace)
H2O
H2SO4
NH4Br/NH4Cl
ROH
organic
phase
organic
phase
pentane
RBr/RCl
ROH
H2SO4 (trace)
H2O (trace)
H2O
aqueous
phase
pentane
NaHCO3
RBr/RCl
ROH (trace)
H2SO4 (trace)
aqueous
phase
H2O (trace)
pentane
RBr/RCl
ROH (trace)
H2O (trace)
H2O
H2SO4
ROH
H2O
H2SO4
ROH
pentane
RBr/RCl
ROH (trace)
Na2SO4
pentane
RBr/RCl
ROH (trace)
H2O (trace)
H2O
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Gas Chromatography Results: 1-Chloro
pentane and 1-Bromopentane
:2WSI R
mVolts
s:\iln\chemistry\fall2003-summer2004\spring 2004\chem 354\wandler\competingnucs\np1p_8;45;53 pm.run
15.0
5.332
R-Br
solvent
12.5
10.0
7.5
5.0
R-Cl
4.579
2.5
0.0
X: 3.4135 Minutes
Y: 0.0590 mVolts
-1.5
3.0
3.5
4.0
4.5
5.0
5.5
Minutes
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Gas Chromatography Results:
1-Chloropentane and 1-Bromopentane
from 1-pentanol
Ret. Time
Width
Peak Peak
Result Time Offset Area
Sep. 1/2 Status
No. Name
()
(min) (min) (counts) Code (sec) Codes
---- ------------ ---------- ------- ------- ---------- ---- ----- -----1
9.9306
4.579 0.000
2113 BB 1.5
2
90.0694
5.332 0.000
19166 BB 1.4
---- ------------ ========== ------- ======= ========== ---- ----- -----Totals:
100.0000
0.000
21279
Total Identified Counts associated with halides: 21279 counts
Round off the values to:
9.9 % 1-chloropentane
90.1 % 1-bromopentane
Important! Other components may appear on the printout. If so, be sure to
recalculate for only 1-chloro and 1-bromopentane! Make sure that the total
equals 100%
Assume that all response factors = 1.000
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Do the results of this experiment with 1-pentanol
fit with what you expected?
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Gas Chromatography Results: 2-Pentanol
in the solvent nucleophile mixture
:2WSI R
+
SR
2-bromopentane
3-bromopentane
4.852
mVolts
s:\iln\chemistry\fall2003-summer2004\spring 2004\chem 354\wandler\competingnucs\hak2p_9;15;27 pm.run
6
solvent
5
2-chloropentane
3-chloropentane
4.151
4
4.932
3
4.216
2
1
0
X: 3.7785 Minutes
Y: 0.0240 mVolts
-1
3.0
3.5
4.0
4.5
5.0
Minutes
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Gas Chromatography Results: 2-Pentanol
in the solvent nucleophile mixture
Ret. Time
Width
Peak Peak Result Time Offset
Area Sep. 1/2
Status
No. Name
()
(min) (min) (counts) Code (sec) Codes
---- ------------ ---------- ------- ------- ---------- ---- ----- -----1
21.7171 4.151 0.000
4100 BV 1.4
2
11.6505 4.216 0.000
2200 VB 1.5
3
46.7971 4.852 0.000
8835 BV 1.4
4
19.8353 4.932 0.000
3745 VB 1.5
---- ------------ ========== ------- ======= ========== ---- ----- -----Totals:
100.0000
0.000
18880
Total Identified Counts associated with halides: 18880 counts
Important! Other components may appear on the printout. If so,
be sure to recalculate for only the four halides! Make sure that the
total equals 100%
Round off the values to:
21.7 % 2-chloropentane
11.7 % 3-chloropentane
46.8 % 2-bromopentane
19.8 % 3-bromopentane
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Why are we obtaining mixtures of halides
in this reaction?
Time for chalk!!
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Gas Chromatography Results:
2-Methyl-2-butanol in the solvent
nucleophile mixture
I:2RWS
+
SR
mVolts
2-bromo-2-methylbutane
s:\iln\chemistry\fall2003-summer2004\spring 2004\chem 354\wandler\competingnucs\ncdtp_5;28;39 pm.run
2-chloro-2-methylbutane
solvent
4.491
5
3.844
4
3
2
1
0
X: 3.1883 Minutes
Y: 108 mVolts
-0
3.0
3.5
4.0
4.5
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Minutes
Gas Chromatography Results:
2-Methyl-2-butanol in the solvent
nucleophile mixture
Ret. Time
Width
Peak Peak Result Time Offset
Area
Sep. 1/2 Status
No. Name
()
(min) (min) (counts) Code (sec) Codes
---- ------------ ---------- ------- ------- ---------- ---- ----- -----1
44.0704 3.844 0.000
5181 BB 1.4
2
55.9296 4.491 0.000
6575 BB 1.5
---- ------------ ========== ------- ======= ========== ---- ----- -----Totals:
100.0000
0.000
11756
Total Identified Counts for the two halides: 11756 counts
Important! Other components may appear on the printout. If so,
be sure to recalculate for only the two halides! Make sure that the
total equals 100%
Round off the values
44.1 % 2-chloro-2-methylbutane
55.9 % 2-bromo-2-methylbutane
Assume that all response factors = 1.000
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We expect that the reaction of 2-methyl-2-butanol
with the solvent nucleophile mixture to be SN1.
Why didn’t it come out as a 50-50 mixture?
Life is never straightforward!
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Important notice about next
week’s lab lecture
Friday, May 19th
Bond Hall 109
2:00 to 2:50
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Important notice: Final
Exam
The exam will be held in SL 110 rather
than SL 130 on
Thursday, June 8th 3:30-5:30
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