I am facing difficulty in the following problem.

Arrange the following compound in decreasing order of acidity.

cyclohexanol, cyclopentylmethanoic acid, 3,3-dimethylpentan-2-one, 1,4-dioxane

It is clear that conjugate base of (Q) is more stable.hence it is most acidic.in R) there is much steric hinderence so my view is that it should be less acidic.however I am not sure about it.


And this is the type of question for which Professor Mayr made us chemistry students rote memorise typical $\mathrm{p}K_\mathrm{a}$ values. Here are some.

\begin{array}{lc}\hline \text{compound type} & \text{typical }\mathrm{p}K_\mathrm{a}\\ \hline \text{alcohol} & \approx 15 \\ \text{ketone} & \approx 20\\ \text{carboxylic acid} & \approx 5\phantom{0}\\ \text{secondary }\ce{C-H} & \approx 45\\ \hline\end{array}

Therefore, the order is $\mathrm{Q > P > R > S}$

| improve this answer | |
  • $\begingroup$ why the downvote? I would agree with the answer. Carboxylic acids are undoubtedly more acidic than others here. A hydrogen attached to an Oxygen(in OH) should be more acidic than a H attached to a C (in ketone) and there is no reason for an ether to be acidic. $\endgroup$ – Amritansh Singhal Dec 26 '16 at 19:39

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