# Substitution and Elimination Reactions In an alkyl halide (HCl, HBr), the halogen can serve as a leaving group for substitution reactions and elimination reactions due to their ability to stabilize negative charges (both due to their high electronegativity and atomic radius). The alpha ($\alpha$) position is the carbon atom connected directly to the halogen, while the beta ($\beta$) positions are the carbon atoms connected the the $\alpha$ position **Bimolecular Nucleophilic Substitution (Sn2)** reactions proceed through an *inversion of configuration* known as a *back-side attack* because the attacking [[Chemical Reaction Mechanisms|nucleophile]] is forced to make its attack from the back. - Cannot occur with tertiary alkyl halides ### Sn1 Reactions ### Substitution Nucleophilic Bimolecular (Sn2) Reactions **Sn2 (Substitution - Nucleophilic - Bimolecular)** ## Elimination Reactions **E1** - aaa **E2** - aaa Bases and Nucleophiles: ![[Common Strong and Weak Nucleophiles.png|300]] ![[Strong and Weak Bases and Nucleophiles Chart.png]] | Category | $S_n2$ | $S_n1$ | $E2$ | $E1$ | | --- | --- | --- | --- | --- | | Concerted or Stepwise | | | | | | Uses a Base or Nucleophile | | | | | | Strong or Weak Base/Nucleophile | | | | | | Rate Law | | | | | | Uni/Bi Molecular | | | | | | Regio/Stereochemistry | | | | | | Increasing Substitution and Rate | | | | | | Preferred Solvent | | | | | ## Regioselectivity of Elimination Reactions ![[Regioselectivity of E2 Reactions.png|450]] - The **Zaitsev product** is the **more** substituted alkene - The **Hofmann product** is the **less** substituted alkene - typically forms when a sterically hindered base is used