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.

Base-promoted α-halogenation of ketones

1 real reaction from the literature, on aryl ketones. Each scheme shows starting materials, conditions and products, with the yield and reference where the source reports them.

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α-Halogenation (basic): 5,6-difluoro-1-indanone (an aryl ketone) with 2 equiv Br2, KOH gives 2,2-dibromo-5,6-difluoro-3H-inden-1-one (the α-halo ketone).

α-Halogenation (basic)Molecules 2007, 12, 74