Organic Chemistry Compare Acid Strength Worksheet

The nitro group (NO2) is an electron-withdrawing group (EWG). The pKa for meta-nitrophenol (A) is 8.3 and the pKa for para-nitrophenol (B) is 7.1. Use this data to explain the effects of the nitro group on the acidity of phenol. Resonance effects should be considered. Use complete drawings to support your answer (i.e., draw out the nitro group and ALL relevant resonance forms of the conjugate bases).

Consider the following guiding questions as you prepare your explanation:

1) What do the conjugate bases of these phenols look like? (please refer to them as CB-A and CB-B) 2) Are the nitro groups involved in the resonance of CB-A and/or CB-B?

  • Which conjugate base is more stable? Why?
  • How does CB stability correlate to the given pKa data of the parent acids?

pKa 7.1

Explain the difference in acidity:

1) What do the conjugate bases of these phenols look like? (please refer to them as CB-A and CB-B) 2) Are the nitro groups involved in the resonance of CB-A and/or CB-B? 3) Which conjugate base is more stable? Why? 4) How does CB stability correlate to the given pKa data of the parent acids?

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