SN1 reaction

The S_N1 reaction is an organic reaction in chemistry. "S_N" stands for substitution nucleophilic and the "1" represents the fact that the rate-determining step take place on the first order, that is it happens with only one molecule. Increasing or decreasing the concentration of that kind of molecule in a closed system changes the rate of the reaction in a direct relationship.

The S_N1 reaction takes place in two steps:

1. Changing the carbon centre:
   1. Formation of a carbocation: due to the separates of leaving group (molecule A) from the carbon.
   2. Nucleophilic attack: a nucleophile (molecule B) joins onto the carbon.
2. Deprotonation: Removal of a proton on the protonated nucleophile by a molecule (sometimes the same species as A) in the solvent, usually protic.

An example reaction:

1. C(CH₃)₃Br --> C(CH₃)₃⁺ + Br^-
2. C(CH₃)₃⁺ + OH^- --> C(CH₃)₃OH

This gives the overall reaction:

C(CH₃)₃Br + OH^- --> C(CH₃)₃OH + Br^-

SN1 occurs where the central carbon atom is surrounded by bulky groupss. The rate depends only on the concentration of the substrate.

rate = k[RX]

Nucleophilicity is irrelevant in the determining step's rate, in which only the substrate is crucial.

Because the intermediate cation, R⁺, is planar, an optically active substrate gives a racemic mixture because nucleophilic attack can occur from either side.

External links

• Diagrams: Frostburg State University
• Exercise: the University of Maine