Developing Critical Thinking Problems for Organic Chemistry Ray A. Gross, Jr.

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Developing Critical Thinking

Problems for Organic

Chemistry

Ray A. Gross, Jr.

Prince George’s Community

College

1

January 10, 2007

2

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.

3

Nature of the Problems

Focused on developing reasoning skills

Solvable by applying course content

The amount of content is limited

4

Kinds of Problems Available

Spectroscopy

Synthesis

Degradation*

5

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.

6

Example of Ozonolysis

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

9

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

10

Consider the following reaction.

C

3

H

6

O

3

(R)

CH

2

O + C

2

H

4

O

Given only molecular formulas.

11

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

12

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

13

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

14

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.

15

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

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.

17

Producing Solvable Problems

Find structures that are deducible from the two kinds of ozonolysis reactions.

Convert them into anathons.

Join anathons to make unknowns.

18

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

19

(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

20

Join Anathons to Create Unknowns

Anathon

H C H

CH

3

CH

Unknown

H

2

C CHCH

3

H

2

C

CH

3

CH

Internal Anathons

When a molecule is cleaved in two places, the middle compound produces an internal anathon.

22

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 internal anathon

CH

3

CH terminal anathon

23

Carbon-Carbon Triple Bonds

Ozonolysis by either workup gives two carboxylic acids.

24

Cleavage of a Triple Bond

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.

25

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.

26

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.

27

Example of Terminal/Interior Anathon terminal anathon

A second terminal anathon is bonded here.

Three terminal anathons are bonded as indicated.

interior anathon

28

Examples of the Unknowns

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

29

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

30

The approach described might be of use in other chemistry courses or disciplines.

31

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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