"A reaction mechanism is the step by step sequence of elementary reactions by which overall chemical reaction occurs."
The step-by-step sequence of events that occur during a chemical reaction.
Bond dissociation energy: The amount of energy required to break a particular bond in a molecule.
Reaction coordinate: The path followed by the reactants as they transform into the products.
Activation energy: The energy required to reach the transition state from the reactants.
Transition state: The highest-energy point on the reaction coordinate that the reaction must pass through in order to proceed.
Reaction intermediates: The species that are formed during the course of a reaction and are not the initial or final reactants or products.
Catalysts: A substance that increases the rate of a chemical reaction without being consumed in the reaction.
Hammond postulate: The energy of the transition state is closer in energy to the species it is more similar to in structure.
Carbocation stability: The stability of a carbocation is determined by the number of alkyl groups attached to the positively charged carbon.
Nucleophile/electrophile: Nucleophiles are species that donate electrons to attack electrophiles, which are species that accept electrons.
Substitution reactions: A reaction where one atom or group of atoms is replaced by another atom or group of atoms.
Elimination reactions: A reaction where a molecule is split into two products without the addition of any other reactants.
Addition reactions: A reaction where two or more reactants combine to form a larger product.
Rearrangement reactions: A reaction where the atoms in a molecule are rearranged to form a new molecule.
Radical reactions: A reaction where one or more radicals are formed as intermediates.
Lewis acids and bases: A Lewis acid is a species that can accept a pair of electrons, while a Lewis base is a species that can donate a pair of electrons.
Organometallic reactions: A reaction where a metal is attached to an organic molecule.
Solvent effects: The effect of the solvent on the reaction rate and product distribution.
Stereoselectivity: The preference of a reaction for one stereoisomer over another.
Kinetics: The study of the rate of chemical reactions.
Thermodynamics: The study of the energy changes associated with chemical reactions.
Substitution reactions: In these reactions, one or more atoms or molecules are replaced by another atom or molecule. For example, a chlorine atom in a molecule can be replaced by a bromine atom.
Addition reactions: In these reactions, two or more molecules combine to form a single product molecule. For example, the addition of hydrogen to an unsaturated hydrocarbon to form a saturated hydrocarbon.
Elimination reactions: In these reactions, a molecule is removed from a reactant, resulting in the formation of a new product. For example, the elimination of water from an alcohol to form an alkene.
Redox reactions: In these reactions, there is a transfer of electrons from one reactant to another. This results in a change in the oxidation states of the reactants. For example, the reaction between copper and silver nitrate.
Acid-base reactions: In these reactions, a proton (H+) is transferred from one reactant to another. For example, the reaction between hydrochloric acid and sodium hydroxide.
Radical reactions: In these reactions, free radicals are generated as reaction intermediates, which react with other molecules. For example, the reaction between chlorine gas and methane to form chloromethane.
Rearrangement reactions: In these reactions, the arrangement of the atoms in a molecule is changed to form a new product. For example, the rearrangement of a carbocation in a reaction sequence.
Photochemical reactions: In these reactions, a chemical reaction is initiated by absorption of light energy. For example, the chlorination of methane in the presence of ultraviolet light.
Polymerization reactions: In these reactions, small molecules (monomers) are joined together to form larger molecules (polymers). For example, the polymerization of ethene to form polyethylene.
Hydrolysis reactions: In these reactions, water is used to break chemical bonds. For example, the hydrolysis of a peptide bond in a protein molecule.
"A chemical mechanism is a theoretical conjecture that tries to describe in detail what takes place at each stage of an overall chemical reaction."
"The detailed steps of a reaction are not observable in most cases."
"The conjectured mechanism is chosen because it is thermodynamically feasible and has experimental support in isolated intermediates (see next section) or other quantitative and qualitative characteristics of the reaction."
"A complete mechanism must also explain the reason for the reactants and catalyst used, the stereochemistry observed in reactants and products, all products formed and the amount of each."
"The electron or arrow pushing method is often used in illustrating a reaction mechanism; for example, see the illustration of the mechanism for benzoin condensation in the following examples section."
"Often what appears to be a single-step conversion is in fact a multistep reaction." Quotes: