Question

Thoroughly explain the difference in the pK_a's of A) meta-cyanophenol (8.61) and B) para-cyanophenol (7.95) . In other words, which is the stronger acid and WHY? Be sure to clearly address resonance effects. Your response should consider the Guiding Questions. Only 100-400 words.

Guiding questions:

1) What is the relationship between pK_a and acidity?
2) Which is the stronger acid, A or B?
3) What do the conjugate bases of these phenols look like? (please refer to them as CB-A and CB-B)
4) What does the detailed structure of the cyano group look like?
5) Describe the resonance forms of both conjugate bases.
6) Are the cyano groups involved in the resonance? If so, how?
7) What effect does resonance have on the relative acidity of A and B?

Answer 1