Definition

Noun: A chemical reaction in which one molecule combines with another, resulting in a single product. This typically involves the addition of atoms or groups of atoms across a double or triple bond in an unsaturated compound.

Usage

This term is used specifically in the field of chemistry to describe a fundamental type of organic reaction. It contrasts with substitution or elimination reactions. The word "addition" here refers to the act of one substance being added to another without the loss of any atoms from the system.

Examples

• The hydrogenation of an alkene is a classic example of an addition reaction.
• In an addition reaction, the pi bond of the unsaturated reactant is broken.
• The mechanism of this addition reaction involves the formation of a carbocation intermediate.

Advanced Usage

• Regioselectivity in Addition Reactions: This refers to the preference for one direction of addition over another in unsymmetrical alkenes, often explained by Markovnikov's rule.
  • Example: The addition of HBr to propene is a regioselective addition reaction.
• Stereospecific Addition: Some addition reactions, like the syn addition of hydrogen or the anti addition of halogens, produce specific stereoisomers.
  • Example: The bromination of an alkene is a stereospecific addition reaction that yields a racemic mixture of enantiomers.

Variants and Related Words

• Electrophilic Addition: A major subclass where the first step is attack by an electrophile on the pi electrons of a double bond.
• Nucleophilic Addition: A subclass typical for carbonyl compounds (like aldehydes and ketones), where the first step is attack by a nucleophile.
• Radical Addition: An addition reaction initiated by free radicals.
• Cycloaddition: A specific type of addition where two or more unsaturated molecules combine to form a cyclic product (e.g., the Diels-Alder reaction).

Synonyms

• Additive Reaction (less common)
• Adduct Formation (specifically refers to the product, the adduct, being formed)

Related Phrases / Idioms

• Undergo addition: Describes the process of a molecule participating in this reaction.
  • Example: Alkenes readily undergo addition with halogens.
• Anti-Markovnikov addition: A specific outcome where the adding atoms orient themselves opposite to the prediction of Markovnikov's rule.
  • Example: In the presence of peroxides, HBr adds to alkenes via an anti-Markovnikov addition.

Noun

1. a chemical reaction in which one molecule is added to another