The basic strength is determined by the ability of an ion or molecule to accept a proton. How do I know whether RSH is more stable than ROH? (R is an alkyl group)

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    $\begingroup$ My recent answer to this question is quite relevant, with the small difference that one hydrogen gets swapped for an alkyl group. Just remember that stronger acids create weaker conjugate bases. $\endgroup$ – Nicolau Saker Neto Mar 26 '15 at 12:42
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    $\begingroup$ I think it's the other way around. Thiols are more acidic than alcohols so the conjugate base of a thiol is a weaker base than the alcohol conjugate base. $\endgroup$ – RobChem Mar 26 '15 at 15:31

RobChem has already pointed out in his comment that your assumption is not quite correct.

Take a look at $\mathrm{p}K_\mathrm{a}$ values for $\ce{ROH}$ and $\ce{RSH}$ in water from the CRC Handbook of Chemistry and Physics and/or other online sources, such as this or that.

\begin{array}{lrr} \mathbf{R} & {\ce{\mathbf{OH}}} &\ce{\mathbf{SH}}\\ \hline \ce{H} & 15.7 &7.0\\ \ce{Et} & 15.9 & 10.6\\ \ce{(H3C)3C} & 18.0 & 11.7\\ \ce{C6H5} & 9.9 & 6.6\\ \end{array}

In all the cases above, the $\mathrm{p}K_\mathrm{a}$ value for $\ce{RSH}$ is smaller than that of $\ce{ROH}$.


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