What is the difference between a sn1 and sn2 reaction?

Question

Sarah Angotti · Accepted Answer

Their names are the most obvious difference!

SN1 reactions are stepwise, unimolecular processes in which,

#"R" = k["LG"^(-)]#

SN2 reactions are coordinated, bimolecular processes in which,

#"R" = k["LG"^-]["Nu"]#

Because a nucleophile replaces a leaving group—a substituent that is likely to depart—these reactions are known as nucleophilic substitutions.

Each is sensitive to different reaction conditions, which are determined by the rate laws. SN1 requires a very strong leaving group, a stable substrate that can form a carbocation intermediate through hyperconjugation or resonance, and a relatively weak nucleophile, which is why neutral nucleophiles are present.

SN2 needs an amazing nucleophile, that isn't bulky, to substitute the leaving group in one concerted step. Hence, polar aprotic solvents are nearly always needed (#H_2O# could be used with #NaOH#, which is an exception that I remember my professor getting me with).

Is all of this very confusing? If so, you haven't done enough work with problem sets. Many students who aren't motivated to put in the effort and practice the material diligently fall out of organic chemistry at this point.

Isabella Acosta · Answer

undefined The main difference between SN1 and SN2 reactions lies in their mechanisms and the rate-determining steps. SN1 reactions proceed through a two-step mechanism involving the formation of a carbocation intermediate, followed by nucleophilic attack. They are favored in polar protic solvents and occur predominantly with tertiary alkyl halides. SN2 reactions, on the other hand, proceed through a single-step mechanism where the nucleophile attacks the substrate simultaneously as the leaving group departs. They are favored in polar aprotic solvents and occur predominantly with primary alkyl halides. Additionally, SN2 reactions exhibit second-order kinetics, whereas SN1 reactions exhibit first-order kinetics.