The SN1 reaction is an organic reaction in chemistry. "SN" stands for substitution nucleophilic and the "1" represents the fact that the rate-determining step is unimolecular. 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 SN1 reaction takes place in two steps: # Formation of a carbocation by separation of leaving group (molecule A) from the carbon. # Nucleophilic attack: a nucleophile (molecule B) joins onto the carbon. If the nucleophile B is a neutral molecule (very often it is a solvent molecule), a third step is required to complete the reaction. 3. Deprotonation: Removal of a proton on the protonated nucleophile by a nearby ion or molecule An example reaction: # (CH3)3CBr --> (CH3)3C+ + Br- # (CH3)3C+ + H2O --> (CH3)3C-OH2+ # (CH3)3C-OH2+ + H2O --> (CH3)3COH + H3O+ This gives the overall reaction: :(CH3)3CBr + H2O --> (CH3)3COH + HBr SN1 occurs where the central carbon atom is surrounded by bulky groups and produces a stable carbocation. 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 carbocation, 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
탄소와 이탈기의 결합이 끊어진 후 친핵체가 탄소 양이온에 결합하는 두단계 과정이다.
① 반응속도는 친핵체의 농도와 무관하다.
② 이탈기를 포함하는 탄소가 입체중심이면, 이 반응이 일어날 때 광학활성을 잃게 된다(즉, 라세미화가 일어난다).
③ 기질의 알킬기가 3차일 때 반응이 가장 빠르고, 1차일 때 가장 느리다.