Addition Reaction General — the NEET Chemistry reaction: mechanism, reagents, conditions, structures and exam traps.
Addition Reaction (General) An addition reaction is an organic reaction where two or more molecules combine to form a larger, single molecule (an adduct) without the loss of any atoms. This typically involves the breaking of a multiple bond (double or triple bond) in the unsaturated substrate and the formation of two new single bonds. Observations are highly specific to the individual addition reaction. Common visual cues include the disappearance of a characteristic color (e.g., reddish-brown bromine water turning colorless in the presence of an alkene), the formation of a precipitate, or a noticeable change in temperature if the reaction is highly exothermic. Generally exothermic, as the breaking of a weaker pi bond and formation of two stronger sigma bonds leads to a net release of energy. However, the specific enthalpy change varies with the reactants. Step 1: The pi bond (or electron-rich center) of the unsaturated molecule acts as a nucleophile, attacking an electrophile (or electron-deficient center). This breaks the multiple bond. Step 2: An intermediate (e.g., carbocation, radical, cyclic ion) is formed. Step 3: A nucleophile (or another radical) attacks the intermediate, forming two new single bonds and completing the adduct. Ignoring regioselectivity (Markovnikov vs. anti-Markovnikov for HBr with peroxides). Overlooking carbocation rearrangements (hydride or alkyl shifts) in electrophilic addition reactions. Incorrectly predicting stereochemistry (syn vs. anti addition, racemic products). Confusing addition reactions with substitution or elimination reactions. Not recognizing the role and specificity of catalysts (e.g., Pt, Pd, Ni for hydrogenation, acid for hydration).