Why Cyclohexatriene (C₆H₆, pK_a = 43) is Less Acidic than Cyclopentadiene (C₅H₆, pK_a = 15) and Cycloheptatriene (C₇H₈, pK_a = 36): A Freshmen Chemical Education Undergraduate Exercise

Sanjeev Rachuru¹, Devarakonda A. Padmavathi² and V. Jagannadham^2,

¹Department of Chemistry, Geethanjali College of Engineering and Technology, Cheeryal-501301, Telangana, India

²Department of Chemistry, Osmania University, Hyderabad-500007, India

Cite this paper

Sanjeev Rachuru, Devarakonda A. Padmavathi and V. Jagannadham. Why Cyclohexatriene (C₆H₆, pK_a = 43) is Less Acidic than Cyclopentadiene (C₅H₆, pK_a = 15) and Cycloheptatriene (C₇H₈, pK_a = 36): A Freshmen Chemical Education Undergraduate Exercise. World Journal of Chemical Education. 2023; 11(1):1-3. doi: 10.12691/WJCE-11-1-1

Abstract

The pK_a of Cyclohexatriene (Benzene) is 43. And that of Cyclopentadiene and Cycloheptatriene are 15 and 36 respectively. In the ascending order of number of carbon atoms of the three cyclic hydrocarbons, Cyclohexatriene lies between Cyclopentadiene and Cycloheptatriene. It is a tempting belief of undergraduate chemists who begin to pursue their undergraduate course that the pK_as will be in the same increasing order with increase in ring size. But surprisingly pK_a of Cyclohexatriene is more than that of either Cyclopentadiene and or Cycloheptatriene. Suitable explanations are given.

Keywords

Cyclohexatriene, Cyclopentadiene, Cycloheptatriene and pK_a

Copyright

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