Teaching Substitution and Elimination
With Real-Life Examples
Bob Hanson
St. Olaf College, Northfield, MN
http://www.stolaf.edu/people/hansonr
20th Biennial Conference on Chemical Education
Indiana University
July 29, 2008
Road Map for This Presentation
• Background: Data-Driven Chemistry
• The Course: 1st Semester Organic
• The Data: 39 reactions
• The Exam: 25 questions
• Conclusions
Background: “Data-Driven” Chemistry
generate data
extrapolate hypotheses
analyze data
generate hypotheses
Background: “Data-Driven Chemistry”
• Start with raw data
• Transform the data into
meaningful information
• Create a working model
R. M. Hanson, S. A. Bergman,
"Data-Driven Chemistry: Making Molecular Models (Literally)
from Electron Diffraction Data”, J. Chem. Educ. 1994, 150
Background: focus on analysis
generate data
(experimental)
analyze data
(identify trends)
extrapolate hypothesis
(predict shapes)
generate hypothesis
(explain shapes
and trends)
Application: organic chemistry
generate data
(experimental)
analyze data
(identify trends)
extrapolate hypothesis
(predict reactions)
generate hypothesis
(explain reactions)
The Course
1st semester of a standard two-semester course
55 students in my section (approx. 120 students total):
39 sophomores
13 juniors
3 seniors
Textbook: Paula Bruice, Organic Chemistry, 5th ed.
Focus: substitution and elimination
generate data
(experimental)
analyze data
(identify trends)
extrapolate hypothesis
(predict reactions)
generate hypothesis
(explain reactions)
Data Sources
Ingold, Structure and Mechanism in Organic Chemistry,
2nd Ed., 1969
Compendium of Organic Synthetic Methods, 1971
M: March, Advanced Organic Chemistry, 3rd Ed., 1985
V: Vogel, Textbook of Practical Organic Chemistry, 5th
Ed., 1989
The Data
The Data
The Data
The Data
The Data
The Data
The Data
The Data
The Data
The Data
The Exam
• 55 minutes
• 25 multiple-choice questions
• Instructions:
In each case, read each possible answer, use a process of
elimination, and circle the BEST answer. If you are having
trouble deciding between two answers, briefly explain your
final choice. If you do so, use just a few words, just to clue
me in to what you are thinking. Do not dwell on any
particular problem for an extended period of time. Each
question is worth 2 points.
The Exam
The Exam
The Exam
The Exam
The Exam
The Exam
The Exam
The Exam
The Exam
The Exam
The Exam
The Exam
The Exam
The Exam
The Exam
The Exam
The Exam
average score: 75%
(average exam score for the semester: 73%)
three additional questions
The Exam
This test was:
(a) Easier than I thought it would be.
(b) Somewhat harder than I thought it would be.
(c) WAY harder than I thought it would be.
The Exam
This test was:
(a) Easier than I thought it would be.
15
(b) Somewhat harder than I thought it would be. 14
(c) WAY harder than I thought it would be.
1
(d) Maybe a bit harder.
1
(e) About as hard as expected.
16
(f) Not too bad.
1
The Exam
I think looking at the data this way…
“…is GREAT, I learned a lot!”
“…seems to apply to the real world
more so than the book.”
“…makes for an interesting way of learning
about these reactions.”
“…really works with the way I think. I liked it a lot!”
The Exam
I think looking at the data this way…
“…is GREAT, I learned a lot!”
“…seems to apply to the real world
more so than the book.”
“…makes for an interesting way of learning
about these reactions.”
“…really works with the way I think. I liked it a lot!”
“…you can see and think through all parts of the
reaction, doesn’t feel as much like memorization
and regurgitation of info…you can think through
why an answer is right or wrong in comparison with
others.”
Conclusions 1/3
• For the most part, students “got it.”
• Generally, students did not have trouble with the
definitions of SN1, SN2, E1, and E2.
• A significant number of the students were still having
trouble identifying strong and weak bases.
Conclusions 2/3
• Stereochemical concepts and notation were integrated
into 6 of the 25 questions (24%). For these questions, 77%
of the responses were correct.
• However, proper axial/equatorial analysis was critical
for 4 of those 6 questions, and for those, the average was
somewhat lower – 68%.
Conclusions 3/3
• Using a data-driven approach can work in organic chemistry.
• Students rise to the challenge of guided inquiry.
• Substitution and Elimination are still difficult concepts!
Thank you!
This presentation is available at
http://www.stolaf.edu/depts/chemistry/bh/bcce20