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.

[1,5]-Hydrogen sigmatropic shift

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

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[1,5]-H sigmatropic shift: a cyclic conjugated diene with 225 C; [1,5] H shift gives the isomerized diene.

[1,5]-H sigmatropic shiftHelv. Chim. Acta 1970, 53, 173
[1,5]-H sigmatropic shift: a cyclic conjugated diene with 240 C; [1,5] H shift gives 1,2,3-triphenyl-1H-indene (the isomerized diene).

[1,5]-H sigmatropic shiftJ. Am. Chem. Soc. 1971, 93, 650