Which anion is more acidic: TsO- or CN-?

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Discussion Overview

The discussion centers on the acidity of the anions TsO- (tosylate) and CN- (cyanide), specifically comparing their corresponding acids TsOH and HCN. Participants explore the implications of acidity and basicity in the context of substitution reactions and leaving group abilities.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • One participant claims that TsOH is more acidic than HCN, citing pKa values of around -7 for TsOH and around 9 for HCN.
  • Another participant introduces the idea that when considering the basicity of the anions, the basic strengths are reversed, with sodium cyanide being a strong base compared to sodium tosylate.
  • A participant expresses interest in comparing the leaving abilities of TsO- and CN- in substitution reactions, noting that the stronger the acid, the weaker its conjugate base, which affects leaving group ability in SN2 reactions.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the comparison of acidity and basicity, as differing perspectives on the implications of the anions' properties are presented.

Contextual Notes

Participants mention the need to consider the basic equivalents of the acids and their conjugate bases, indicating that assumptions about acidity and basicity may depend on specific contexts and definitions.

maverick280857
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Which is more acidic: TsOH or HCN? (Ts is p-MeC6H4SO2-).
 
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TsOH. TsOH has a pKa around -7, HCN is around 9.
 
You may think from the reverse side; if you have the basic equivalents of these acids, the basicities are reversed. Let me give an example, sodium salts of these acids are bases, but sodium cyanide is a very strong base whereas sodium tosylate is not that strong.
 
chem_tr said:
You may think from the reverse side; if you have the basic equivalents of these acids, the basicities are reversed. Let me give an example, sodium salts of these acids are bases, but sodium cyanide is a very strong base whereas sodium tosylate is not that strong.

:smile: Yeah I was working on this substitution reaction when this came along so I wanted to compare the leaving abilities of TsO- and CN- hence this problem. I did not know anything about their basic strengths. Instead we've been told to make acids from these anions (conjugate) and compare their acidic strengths. The stronger the acid, we weaker its conjugate base and correspondingly, the greater its leaving ability in a SN2 rxn.

Thanks and Cheers
Vivek
 

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