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.

[2+2] Cycloaddition

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

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[2+2] cycloaddition: 1,3-butadiene (a conjugated diene) with hν; sensitizer; trans >> cis gives 1,2-diethenylcyclobutane.

[2+2] cycloadditionOrg. Synth. Coll. Vol. 5, p. 528