1
Developing Critical Thinking Problems for Organic
Chemistry
Ray A. Gross, Jr.
Prince George’s Community College
2
January 10, 2007
3
Thoughts About Students
• 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.
4
Nature of the Problems
• Focused on developing reasoning skills• Solvable by applying course content • The amount of content is limited
5
Kinds of Problems Available
• Spectroscopy
• Synthesis
• Degradation*
6
Concept of Degradation
A compound of unknown structure is broken down into smaller pieces, which can be reassembled in a logical way to determine the structure.
7
Example of Ozonolysis
+CH3CH2CCH3
O
CH3CH2CH
O
Xunknownhydrocarbon
(1) O3
(2) Zn/H+
remove oxygen
CH3CH2CCH3+ CH3CH2CH
anathons
CH3CH2CCH3
HCCH2CH3
analyte
8
O3
(R)
C7H14C4H8O C3H6Oketone aldehyde
+
+
C4H8C3H6
anathons
analyte
Cleavage of a double bond yields two carbonyl compounds,aldehydes or ketones.
9
Some Aldehydes may be identified by their molecular formulas.
C
O
H HCH2O = C
H H
molecularformula
structuralformula
anathon
10
=
molecularformula
structuralformula
anathon
C2H4OC
O
CH3 HC
CH3 H
Some Aldehydes may be identified by their molecular formulas.
11
Consider the following reaction.
C3H6
O3
(R)CH2O + C2H4O
Given only molecular formulas.
12
Anathons are like building blocks.
C3H6
O3
(R)CH2O + C2H4O
CH H
O+
CH3CH
O
CH H CH3CH
+
CH
HC
H
CH3
propene
13
+CH3CH2CCH3
O
CH3CH2CH
O
(1) O3
(2) Ag2O
(1) O3
(2) Zn/H+
CH3CH2CCH3
O
CH3CH2COH
O
+
ketone
ketone
aldehyde
acidCH3CH2C CHCH2CH3
CH3
Ketones remain ketonesAldehydes are oxidized to acids
14
(1) O3
(2) Ag2O
(1) O3
(2) Zn/H+
+C7H14
C4H8O C3H6O2
C4H8O C3H6O+
Same reactions using molecular formulas.
15
Identify aldehydes and ketones.
(1) O3
(2) Ag2O
(1) O3
(2) Zn/H+
+C7H14
C4H8O C3H6O2
C4H8O C3H6O+
no change
ketone
plus 1 O
aldehyde
Result: A four-carbon ketone and a three-carbon aldehyde.
16
Place C atoms in logical locations to find anathons.
Connection of anathons reveals the unknown’s structure.
C7H14C4H8O C3H6O
ketone aldehyde
anathons
17
Concept
• 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.
18
Producing Solvable Problems
• Find structures that are deducible from the two kinds of ozonolysis reactions.
• Convert them into anathons.• Join anathons to make unknowns.
19
Structures from Molecular Formulas
CH2O CO2 H C H
O
C2H4O C2H4O2 CH3CH
O
C3H4O C3H4OO
(R) (O) R product
20
Remove Oxygen to form Anathons
CH2O CO2 H C H
O
C2H4O C2H4O2 CH3CH
O
C3H4O C3H4OO
(R) (O) R product Anathon
H C H
CH3CH
21
Join Anathons to Create Unknowns
Anathon
H C H
CH3CH
H2C CHCH3
H2C
CH3CH
Unknown
The process ensures solvable structures are produced.
22
Internal Anathons
• When a molecule is cleaved in two places, the middle compound produces an internal anathon.
23
Example of an Internal Anathon
H2C CHCH2CH=CHCH3
O3 (O)
O3 (R) CH2O + C3H4O2 + C2H4O
CO2 + C3H4O4 + C2H4O2
HCH HCCH2CH CH3CH
terminal anathon
terminal anathon
internal anathon
24
Carbon-Carbon Triple Bonds
• Ozonolysis by either workup gives two carboxylic acids.
25
Cleavage of a Triple Bond
CH3C CCH2CH3
CH3CO2H + CH3CH2CO2H
CH3CO2H + CH3CH2CO2HO3 (O)
O3 (R)C5H8
A triple bond in the analyte leads to two new hydrogen atoms and four new oxygen atoms.
26
O3 (R)C5H8 C2H4O2 C3H6O2+
2 new H atoms = triple bond two caboxylic acids
CH3C CCH2CH3
Anathons from triple bonds have three bonding sites, andthose from double bonds have two.
27
Anathons Readily Determined by their Ozonolysis Products
• 11 Terminal Anathons
• 11 Interior Anathons
• 3 Either Terminal or Interior
306 unique unknown hydrocarbons can be producedfrom the 22 anathons. All of them are solvable by the techniques shown.
28
Example of Terminal/Interior Anathon
terminal anathon
A secondterminal anathon is bonded here.
interior anathon
Threeterminal anathons are bonded as indicated.
29
Examples of the Unknowns
CH3CH2CH CHCH2CH C(CH3)2
CH3CH2CH C CCH3
CH2CH3
CHC CCH2CH3
30
Problems Created that:
• 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
31
The approach described might be of use in other chemistry courses or disciplines.
32
Problems of this type are available in the following references.
Chemical Educator 2006, 11, 372-377.
Journal of Chemical Education 2006, 83, 604-609.
Top Related