How do you predict whether a reaction will undergo sn1 or sn2?

Question

Nolan Allen · Accepted Answer

How much shrubbery is there around the ipso carbon?

Now of course #S_N1# and #S_N2# reactions are DISSOCIATIVE (i.e. bond-breaking), and ASSOCIATIVE (bond-making) respectively to a first approximation. Associative mechanisms are largely restricted to methyl, primary, and more rarely, secondary, carbon centres. However, we need information and context. On the other hand, a dissociative, bond-breaking mechanism is more likely if there is some degree of steric bulk surrounding the ipso carbon.

Ava Andrews · Answer

undefined The prediction of whether a reaction will undergo SN1 (substitution nucleophilic unimolecular) or SN2 (substitution nucleophilic bimolecular) mechanism depends on several factors:

1. Substrate: SN1 reactions typically occur with tertiary or secondary substrates, while SN2 reactions occur with primary or methyl substrates.
2. Nucleophile: SN2 reactions favor strong nucleophiles, while SN1 reactions are less affected by nucleophile strength.
3. Solvent: Polar aprotic solvents favor SN2 reactions, whereas polar protic solvents favor SN1 reactions.
4. Leaving group: Good leaving groups facilitate both SN1 and SN2 reactions, but SN2 reactions are more sensitive to leaving group ability.
5. Stereochemistry: SN2 reactions proceed with inversion of configuration, while SN1 reactions do not have a strict stereochemical outcome.
6. Reaction kinetics: SN2 reactions are typically faster than SN1 reactions due to the concerted nature of the SN2 mechanism.