Developing Critical Thinking Problems for Organic Chemistry

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

8. Cleavage of a double bond yields two carbonyl compounds, aldehydes or ketones.

9. Some Aldehydes may be identified by their molecular formulas.

10. Some Aldehydes may be identified by their molecular formulas.

11. Consider the following reaction. Given only molecular formulas.

12. Anathons are like building blocks. propene

13. Ketones remain ketones Aldehydes are oxidized to acids

14. Same reactions using molecular formulas.

15. Identify aldehydes and ketones. 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.

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

20. Remove Oxygen to form Anathons

21. Join Anathons to Create Unknowns 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

24. Carbon-Carbon Triple Bonds • Ozonolysis by either workup gives two carboxylic acids.

25. Cleavage of a Triple Bond A triple bond in the analyte leads to two new hydrogen atoms and four new oxygen atoms.

26. Anathons from triple bonds have three bonding sites, and those 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 produced from the 22 anathons. All of them are solvable by the techniques shown.

28. Example of Terminal/Interior Anathon

29. Examples of the Unknowns

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.