Acidic strength of organic acid depends on two factors – inductive and resonance effect.

Now, electron donating groups have +I effect. As a result of which they increase electron density around carbon and adjacent atoms. It results in increased electron density in $\ce{C-O-H}$ bond of acid, making the release of proton difficult. So effect of electron releasing group is that it decreases the acidity of acid.

The trimethyl silicon ($\ce{Me3Si}$) is also electron releasing group but it has lesser donating tendency than trimethyl carbon, $\ce{Me3C}$. Therefore, $\ce{Me3Si}$ inductive effect is lesser than $\ce{Me3C}$ group. Consequently, $\ce{Me3SiCH2COOH}$ is more acidic than $\ce{Me3CCH2COOH}$.

Is this right? Actually, my book writes that $\ce{Me3SiCH2COOH}$ is lesser acidic than $\ce{Me3CCH2COOH}$.

  • $\begingroup$ I suppose the electronegavity of C is more than Si and hence C resists a bit in inductive effect than Si $\endgroup$ – Suraj S May 6 '17 at 7:28

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