Addition Reactions
Addition Reactions - Related Videos
02:15
Preparation of Alcohols via Addition Reactions
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2023
Overview The acid-catalyzed addition of water to the double bond of alkenes is a large-scale industrial method used to synthesize low-molecular-weight alcohols. An acidic atmosphere is required to allow the hydrogen in the water molecule to act as an electrophile and attack the double bond in an alkene. The addition of a proton to the double bond creates a carbocation intermediate. The proton preferentially bonds to the less substituted end of the double bond to create a more stable carbocation...
01:15
Acid-Catalyzed Aldol Addition Reaction
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2025
The aldol reaction of a ketone under acidic conditions successfully forms an unsaturated carbonyl as the final product instead of an aldol. The acid-catalyzed aldol reaction is depicted in Figure 1. Figure 1. The acid-catalyzed aldol addition reaction of ketones. First, as shown in Figure 2, the acid protonates the ketone molecule to form the protonated ketone. The conjugate base of the acid deprotonates the α carbon of the protonated ketone to form the enol. Figure 2. Formation of the enol.
02:24
Introduction to Electrophilic Addition Reactions of Alkenes
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2023
The double bond in a simple, unconjugated alkene is a region of high electron density that can act as a weak base or a nucleophile. The filled π orbital (HOMO) of the double bond can interact with the empty LUMO of an electrophile. A bonding interaction occurs when the electrophile attacks between the two carbons; the electrophile then accepts a pair of electrons from the π bond and undergoes addition across the double bond, yielding a single product. Addition and elimination reactions can be...
01:08
Base-Catalyzed Aldol Addition Reaction
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2025
As depicted in Figure 1, base-catalyzed aldol addition involves adding two carbonyl compounds in aqueous sodium hydroxide to form a β-hydroxy carbonyl compound. Figure 1: The base-catalyzed aldol addition reaction of aldehydes. The reaction preferentially occurs with simple aldehydes, where the α carbon is monosubstituted. The equilibrium of the reaction involving disubstituted aldehydes and ketones shifts backward to the reactants due to the steric interactions at the α carbon. The...
01:27
Conjugate Addition (1,4-Addition) vs Direct Addition (1,2-Addition)
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2025
α,β-Unsaturated carbonyl compounds with two electrophilic sites, the carbonyl carbon, and the β carbon, are susceptible to nucleophilic attack via two modes: conjugate or 1,4-addition and direct or 1,2-addition. Conjugate addition results in a thermodynamically stable product. The reaction retains the stronger C=O bond at the expense of the weaker C=C π bond. The process is slow as the β carbon is less electrophilic than the carbonyl carbon. Direct addition products are formed faster owing to...
FAQs
The key bond-level change is conversion of a carbon-carbon π bond into new σ bonds. As the π bond breaks, the reacting atoms or groups attach to the previously unsaturated carbon framework without an overall loss of atoms. This reorganization changes the molecule’s connectivity, allowing chemists to predict product structures from the original double or triple bond and the added reagent.
These pathways differ mainly in the type of intermediate or reactive process generated by the reactants and conditions. Electrophilic pathways involve electron-seeking behavior, nucleophilic pathways involve electron-rich species, and radical pathways involve radical intermediates. Recognizing the pathway helps explain why different reactants can produce different products from similar unsaturated starting materials.
Selectivity depends on the reactants and the conditions that determine whether an electrophilic, nucleophilic, or radical pathway operates. Those choices influence how new groups attach across a double or triple bond and therefore which product structure predominates. Controlling selectivity is important because it enables more efficient synthetic routes and reduces uncertainty when designing target molecules.
These examples show that the identity of the added reagent determines the groups incorporated into the unsaturated molecule. Hydrogenation, halogenation, and hydration therefore provide distinct product types while following the same broad bond-reorganization logic. Comparing them helps chemists connect reagent choice with product structure and select an appropriate transformation during organic synthesis.
Chemists use these transformations to modify molecules containing carbon-carbon double or triple bonds and to build desired product structures. By considering the starting unsaturation, the reagent, and the likely mechanistic pathway, they can choose a reaction that introduces useful atoms or groups. This planning supports efficient routes to pharmaceuticals, fuels, and other organic products.
Addition polymerization links unsaturated monomers into larger materials, extending the same type of bond reorganization across many molecules. The process converts smaller starting units into polymeric structures without the atom-elimination pattern associated with other reaction types. Its importance lies in connecting molecular-scale reactivity with the preparation of useful materials and in explaining how monomer structure contributes to polymer formation.