When water in presence of any acid is added to a carbonyl compound, it leads to the formation of its hydrate. But how do we determine the rate of reaction? Is it done by checking the amount of partial positive charge on carbonyl compound (by electron withdrawing group attached to carbonyl carbon)?


closed as off-topic by Mithoron, Todd Minehardt, bon, ron, M.A.R. Feb 18 '18 at 19:05

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The formation of the hydrate of any carbonyl compound has the rate determining step as the nucleophilic addition of a water molecule to the electophilic carbon atom of the carbonyl group.

Hence, any electron withdrawing group, like fluoro or nitro, attached in the chain next to the carbonyl group will favor the product side of the equilibrium.

On the other hand, extra branching at the alpha position due to methyl/t-butyl groups will cause steric hindrance, while electron releasing groups will reduce the carbon's electrophilicity, both favoring the reactant side of the equilibrium instead.

It is important to note that while the hydration of alkenes goes to completion, the hydration of carbonyls does not. Hence, ignoring a few exceptions like formaldehyde, ninhydrin, chloral, etc., an equilibrium is setup during hydration of carbonyls. Therefore, it is better to talk about the position of equilibrium in this process rather than the rate of the reaction, as correctly pointed out by @Mithoron.


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