In deciding which reagent to use for a particular transformation consider the difference in composition of reactants and products:
- If the difference between the molecular formula for the reactant and product is two hydrogens, one oxygen or two oxygens, remember that reaction with
- oxidants (such as H2CrO4 or KMnO4) react with organic molecules to increase the number of bonds from carbon to oxygen
- reductants (such as H2 or LiAlH4) react with organic molecules to increase the number of bonds from carbon to hydrogen
- If not, classify the type of reaction based on structural differences between the organic reactant and product.
- Addition reactions result in a product having a lesser degree of unsaturation (fewer multiple bonds).
The difference between the elemental composition of the reactant and product may give directly the reagent required.
- Elimination reactions result in an increase in the degree of unsaturation.
If the reactant is an alkyl halide, strong base (OH– for example) is required.
If the reactant is an alcohol strong acid is required.
- Substitution reactions result in replacement of an atom or group of atoms.
The difference in composition of reactant and product indicates the reagent directly or is part of the reagent required (Br in NaBr, CH3O in CH3ONa or NH3).