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.

Pinacol rearrangement

2 real reactions from the literature, on 1,2-diols. Each scheme shows starting materials, conditions and products, with the yield and reference where the source reports them.

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Pinacol rearrangement: pinacol (a 1,2-diol) with H2SO4; Δ gives pinacolone (the methyl ketone).

Pinacol rearrangementOrg. Synth. Coll. Vol. 1, p. 462
Pinacol rearrangement: benzopinacol (a 1,2-diol) with I2, AcOH; Δ gives 1,2,2,2-tetraphenylethanone (the aryl ketone).

Pinacol rearrangementOrg. Synth. Coll. Vol. 2, p. 73