Quiz - SN Reactions II | Alkyl Halides - Nucleophilic Substitutions

The neighboring groups of the carbocation are important: electron-donating groups (such as alkyl groups) stabilize a positive charge. The more stable the intermediate carbocation, the faster the SN1 reaction

• Polar protic solvents (H₂O, ROH, RCOOH) favor SN1 reactions because the carbocation intermediates are stabilized by solvation
• Polar aprotic solvents (CH₃CN, ROR, DMSO) favor SN2 reactions because the nucleophiles are not well solvated and are therefore more nucleophilic

The strong nucleophile ^-CN with a net negative charge and the polar aprotic solvent CH₃CN favor an S_N2 process. In this two-step process, a bond is broken then a new bond is formed, and inversion of configuration occurs. The nitrile produced is:

The strong nucleophile ^-OH with a net negative charge and the polar aprotic solvent DMSO favor an S_N2 process. In this two-step process, a bond is broken then a new bond is formed, and inversion of configuration occurs. The alcohol produced is:

Steric effects are particularly important in S_N2 reactions:

Allylic and benzylic halides undergo S_N2 reactions more rapidly than the corresponding simple alkyl halides

1 is a vinylic halide, 2 is an allylic halide, 3 is secondary alkyl halide
Allylic and benzylic halides undergo SN2 reactions more rapidly than the corresponding simple alkyl halides, whereas vinylic halides do not undergo SN2 reactions