Abstract

Sanjeev Rachuru*¹, Jagannadham Vandanapu² and Sreedhar Pandiri¹

DOI : http://dx.doi.org/10.13005/ojc/350160

Hammett equation is applied and the magnitude of substituent effect in terms of Hammett ρ has been estimated for the deprotonation equilibriums of highly unstable arenium ions (Wheland intermediates) XC₆ H₆⁺ ⇌ XC₆ H₅ + H⁺ based on the attenuation effect of methylene group on the dissociation equilibriums of anilinium ions, benzyl ammonium ions and 2-phenylethyl ammonium ions. The Hammett ρ was found to be 14.3. The Hammett ρ for the deprotonation equilibriums of pyridinium ions XC₅ H₄NH⁺ ⇌ XC₅ H₄N + H⁺ was estimated from the plot of log K_a vs Hammett σ, this value is 5.90. The magnitude of substituent effect in terms of Taft ρ* has been estimated for the deprotonation equilibriums of methanium ions RCH₄⁺ ⇌ RCH₃ +H⁺ based on the attenuation effect of methylene group on the dissociation equilibriums of aliphatic amines and was found to be 6.9. The Taft ρ* for the deprotonation equilibriums of alkyl ammonium ions RNH₃⁺ ⇌ RNH₂ + H⁺ was estimated from the plot of log K_a vs Taft σ*, this value is 3.28. The large differences in the Hammett ρ of 8 units when carbon is replaced with nitrogen as hetero atom in the six-member aromatic ring and 3.6 units of Taft ρ* when carbon is replaced with nitrogen in aliphatic derivatives respectively is explained.

Arenium Ions and Methanium Ions; Hammett Equation; Taft Equation

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