Developing Critical Thinking
Problems for Organic
Chemistry
Ray A. Gross, Jr.
Prince George’s Community
College
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January 10, 2007
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• They do not spend enough time working problems.
• They need to be taught (learn) how to reason.
• One way to force them to reason is to give them problems they have not seen before.
3

• Focused on developing reasoning skills
•
Solvable by applying course content
•
The amount of content is limited
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• Spectroscopy
• Synthesis
• Degradation*
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A compound of unknown structure is broken down into smaller pieces, which can be reassembled in a logical way to determine the structure.
6

X unknown hydrocarbon
(1) O
3
(2) Zn/H
+
O
CH
3
CH
2
CCH
3
+
O
CH
3
CH
2
CH remove oxygen
HCCH
2
CH
3
CH
3
CH
2
CCH
3 analyte
CH
3
CH
2
CCH
3
+
CH
3
CH
2
CH anathons
7

C
7
H
14 analyte
O
3
(R)
C
4
H
8
O ketone
+
+
C
3
H
6
O aldehyde
C
4
H
8 anathons
C
3
H
6
Cleavage of a double bond yields two carbonyl compounds, aldehydes or ketones.
8

Some Aldehydes may be identified by their molecular formulas.
CH
2
O
= molecular formula
O
H
C
H structural formula
H
C
H anathon
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Some Aldehydes may be identified by their molecular formulas.
C
2
H
4
O molecular formula
=
CH
3
O
C
H structural formula
CH
3
C
H anathon
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Consider the following reaction.
C
3
H
6
O
3
(R)
CH
2
O + C
2
H
4
O
Given only molecular formulas.
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Anathons are like building blocks.
O
3
C
3
H
6
CH
2
O + C
2
H
4
O
(R)
O
H
C
H
+
O
CH
3
CH
H
C
H
C
CH
3
H propene H
C
H
+
CH
3
CH
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CH
3
CH
3
CH
2
C CHCH
2
CH
3
(1) O
3
(2) Ag
2
O
O
CH
3
CH
2
CCH
3 ketone
+
O
CH
3
CH
2
C O H acid
(1) O
3
(2) Zn/H
+
O
CH
3
CH
2
CCH
3
+ ketone
O
CH
3
CH
2
CH aldehyde
Ketones remain ketones
Aldehydes are oxidized to acids
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C
7
H
14
Same reactions using molecular formulas.
(1) O
3
(2) Ag
2
O
(1) O
3
(2) Zn/H
+
C
4
H
8
O +
C
3
H
6
O
2
C
4
H
8
O + C
3
H
6
O
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Identify aldehydes and ketones.
C
7
H
14
(1) O
3
(2) Ag
2
O
(1) O
3
(2) Zn/H
+
C
4
H
8
O +
C
3
H
6
O
2 no change
C
4
H
8
O ketone
+ plus 1 O
C
3
H
6
O aldehyde
Result: A four-carbon ketone and a three-carbon aldehyde.
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Place C atoms in logical locations to find anathons.
C
7
H
14
C
4
H
8
O ketone
C
3
H
6
O aldehyde anathons

• Degradation of an unknown leads to products.
• The structure of each degradation product can be determined directly or indirectly from the two kinds of ozonolysis.
• The products can then be converted into anathons, which are connected in a logical way to produce the starting compound.
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Producing Solvable Problems
• Find structures that are deducible from the two kinds of ozonolysis reactions.
• Convert them into anathons.
• Join anathons to make unknowns.
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Structures from Molecular Formulas
(R)
CH
2
O
C
2
H
4
O
C
3
H
4
O
(O)
CO
2
C
2
H
4
O
2
R product
O
H C H
O
CH
3
CH
O
C
3
H
4
O
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(R)
CH
2
O
C
2
H
4
O
C
3
H
4
O
Remove Oxygen to form Anathons
(O)
CO
2
C
2
H
4
O
2
R product
O
H C H
O
CH
3
CH
O
C
3
H
4
O
Anathon
H C H
CH
3
CH
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Join Anathons to Create Unknowns
Anathon
H C H
CH
3
CH
Unknown
H
2
C CHCH
3
H
2
C
CH
3
CH

• When a molecule is cleaved in two places, the middle compound produces an internal anathon.
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Example of an Internal Anathon
H
2
C CHCH
2
CH =CHCH
3
O
3
(O)
O
3
(R)
CO
2
+ C
3
H
4
O
4
+ C
2
H
4
O
2
CH
2
O + C 3
H
4
O
2
+ C
2
H
4
O
HCH terminal anathon
HCCH
2
CH CH
3
CH internal anathon terminal anathon
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Carbon-Carbon Triple Bonds
• Ozonolysis by either workup gives two carboxylic acids.
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O
3
(O)
CH
3
C CCH
2
CH
3
C
5
H
8
O
3
(R)
CH
3
CO
2
H + CH
3
CH
2
CO
2
H
CH
3
C O
2
H + CH
3
CH
2
C O
2
H
A triple bond in the analyte leads to two new hydrogen atoms and four new oxygen atoms.
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2 new H atoms = triple bond two caboxylic acids
O
3
(R)
C
5
H
8
C
2
H
4
O
2 +
C
3
H
6
O
2
CH
3
C CCH
2
CH
3
Anathons from triple bonds have three bonding sites, and those from double bonds have two.
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Anathons Readily Determined by their
Ozonolysis Products
• 11 Terminal Anathons
• 11 Interior Anathons
• 3 Either Terminal or Interior
306 unique unknown hydrocarbons can be produced from the 22 anathons. All of them are solvable by the techniques shown.
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Example of Terminal/Interior Anathon terminal anathon
A second terminal anathon is bonded here.
Three terminal anathons are bonded as indicated.
interior anathon
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CH
3
CH
2
CH CHCH
2
CH C(CH
3
)
2
CH
3
CH
3
CH
2
CH C C
CH
2
CH
3
CHC CCH
2
CH
3
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• Students have never seen before
• Require a minimum amount of course content
• Require students to apply logic and reasoning
(synthesis, analysis and evaluation)
• Increase in complexity over the semester
• Allow the instructor to give each student a unique problem each week
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The approach described might be of use in other chemistry courses or disciplines.
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Problems of this type are available in the following references.
Chemical Educator 2006, 11, 372-377.
Journal of Chemical Education 2006, 83, 604-609.
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