Stepwise reaction
In chemistry, a stepwise reaction[1] (also called an overall reaction, complex reaction, and multistep reaction, among others) is a chemical reaction with one or more reaction intermediates, which by definition involves at least two consecutive elementary reactions.
In a stepwise reaction, not all
reactants to the products. A stepwise reaction distinguishes itself from an elementary reaction in which the transformation is assumed to occur in a single step and to pass through a single transition state.[2]
In contrast to elementary reactions which follow the
catalytic reactions, the diffusion may also limit the reaction. In general, however, there is one very slow step, which is the rate-determining step
, i.e. the reaction doesn't proceed any faster than the rate-determining step proceeds.
Organic reactions, especially when involving catalysis, are often stepwise. For example, a typical enol
reaction consists of at least these elementary steps:
- Deprotonation next to (α to) the carbonyl: HC−C=O → C=C−O−
- Attack of enolate: Rδ+ + C=C−O− → R−C−C=O
Rδ+ is an electron acceptor, for example, the carbon of a
carbonyl (C=O). A very strong base, usually an alkoxide
, is needed for the first step.
Reaction intermediates may be trapped in a trapping reaction. This proves the stepwise nature of the reaction and the structure of the intermediate. For example, superacids were used to prove the existence of carbocations.
See also
- Chemical reaction
- Elementary reaction
- Rate equation
- Rate-determining step
- Steady state approximation
- Chemical kinetics
- Lindemann mechanism
External links