Reading a scheme

Start with the conditions. A strong base, an acid, a metal, a peroxide: the reagent line narrows the reaction type before you look at a single bond.
Find what changed. Compare starting material and product atom by atom: which bond formed, which left, and whether the carbon count grew.
Substitution vs. elimination vs. addition is a bookkeeping question: same number of σ bonds, fewer, or more.
Mechanism follows structure. A tertiary or benzylic center with a weak nucleophile points to a cation; a primary center with a strong nucleophile does not.
Every example here is a real reaction with a real citation. The yields are the authors’ own.

Hydrate formation

6 real reactions from the literature, on enols, α-keto acids, α-halo aldehydes and methyl ketones. Each scheme shows starting materials, conditions and products, with the yield and reference where the source reports them.

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Hydrate formation: 2-hydroxy-2-cyclohexen-1-one (an enol) with HClO4; H2O gives 2,2-dihydroxycyclohexan-1-one (the hydrate (gem-diol)).

Hydrate formationJ. Am. Chem. Soc. 1963, 85, 2309
Hydrate formation: pyruvic acid (an α-keto acid) with H2O gives 2,2-dihydroxypropanoic acid (the hydrate (gem-diol)).

Hydrate formationRealOChem worksheet
Hydrate formation: 2-bromobutanal (an α-halo aldehyde) with H2O gives 2-bromobutane-1,1-diol (the hydrate (gem-diol)).

Hydrate formationRealOChem worksheet
Hydrate formation: acetone (a methyl ketone) gives 2,2-propanediol (the hydrate (gem-diol)).

Hydrate formationRealOChem worksheet
Hydrate formation: 1,3-dichloroacetone (an α-halo ketone) with H2O gives 1,3-dichloropropane-2,2-diol (the hydrate (gem-diol)).

Hydrate formationRealOChem worksheet
Hydrate formation: methyl pyruvate (an α-keto ester) with H2O gives methyl 2,2-dihydroxypropanoate (the hydrate (gem-diol)).

Hydrate formationRealOChem worksheet