Covalent hydration carbonyl compounds

There are some special cases where tetrahedral intermediates are unusually stable there are three phenomena which lead to this stability enhancement. The first is an unusually reactive carbonyl (or imine) compound which is very prone to addition. An example of such a compound is trichoroacetaldehyde or chloral, for which the covalent hydrate can be isolated. A simple way to recognize such compounds is to think of the carbonyl group as a (very) stabilized carbocation, bearing an substituent. 

Role of covalent hydration and addition of OH-ions — In aqueous solutions the reductions of some carbonyl compounds, for example of numerous aldehydes [i], and some ketones [ii] as well as of some compounds with azomethine (C=N) bonds [iii] are complicated by hydration-dehydration equilibria. In a re-... 

The reversible addition of water across a double or triple bond (covalent hydration) is frequently observed with carbonyl-containing compounds and certain heteroaromatic compounds in aqueous solution. Initial efforts to calculate the absolute hydration equilibrium for simple carbonyl-containing com-... 

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