CPR Assignment

California State Polytechnic University, Pomona, Dr. Laurie S. Starkey
CPR Assignment: Comparing Acidity of Cyanophenols
The pKa for meta-cyanophenol (A) is 8.61 and the pKa for para-cyanophenol (B) is 7.95. Use this data to
determine the effects of the cyano group on the acidity of phenol. Resonance effects should be considered.
Use scratch paper to carefully draw out the structures of the conjugate bases of A and B (and their
relevant resonance forms) so you can accurately describe those structures in your essay.
Guiding Questions
1) What is the relationship between pKa and acidity? Therefore, which is the stronger acid, A or B?
2) What do the conjugate bases of these phenols look like? (please refer to them as CB-A and CB-B)
3) Describe the resonance forms of both conjugate bases.
4) What does the structure of the cyano group look like?
5) Are the cyano groups involved in the resonance? If so, how?
6) In conclusion, what effect does resonance have on the relative acidity of A and B?
Writing Prompt
Write an essay (between 100–400 words in length) that thoroughly explains the difference in the pKa’s of
meta-cyanophenol (A) and para-cyanophenol (B). In other words, which is the stronger acid and WHY? Be
sure to clearly address resonance effects. Your response should consider the Guiding Questions but should
be written in essay form. Be extremely clear in your written arguments. Avoid using ambiguous nouns
such as “it” – instead, refer to species by their proper names (e.g., A, CB-A, C-2, the cyano group, oxygen
atom, the negative charge, etc.). It is recommended that you work on your essay off-line (word processing
program) so you can easily save and store your work in progress. You can then copy and paste the essay
into CPR.
Please note: your formatting will not be preserved unless you’ve included HTML tags in the essay. For
example, insert the command to start a new paragraph. For emphasis, you can turn on bold or
underline and then turn it off with or . For example, the text “I really liked
chemistry in high school!” will display as “I really liked chemistry in high school!” and pKa
displays as pKa. You can “Preview Text” before submitting to check your HTML formatting.
Grading of CPR Assignment
This assignment will be worth up to 5 points on Exam I (not as extra credit)
CPR score 90-100 = 5 points on 1st midterm
CPR 80-89 = 4 points
CPR 70-79 = 3 points
CPR 60-69 = 2 points
CPR 50-59 = 1 points
CPR score below 50 (or no participation) = 0 points

Download Report