Summary & Applications (Synthesis) SN1 / E1 vs. SN2 / E2

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Elimination Reactions

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Summary & Applications (Synthesis) SN1 / E1 vs. SN2 / E2 23

E2 and E1 Reactions

Substitution vs. Elimination Alkyl halides can undergo SN2, SN1, E2 and E1 Reactions 1) Which reaction conditions favor SN2/E2 or SN1/E1? SN2/E2 reactions are favored by a high concentration of nucleophile/strong base SN1/E1 reactions are favored by a poor nucleophile/weak base 2) What will be the relative distribution of substitution product vs. elimination product?

Consider SN1/E1 vs. SN2/E2 Consider the Substrate

NOTE: a bulky base encourages elimination over substitution

Returning to Sn2 and E2: Considering the differences Can you explain the products? Can you predict the products? 21

Substitution and Elimination Reactions in Synthesis

A hindered alkyl halide should be used if you want to synthesize an alkene

Which reaction produces an ether?

Consecutive E2 Elimination Reactions: Alkynes

Intermolecular vs. Intramolecular Reactions A low concentration of reactant favors an intramolecular reaction The intramolecular reaction is also favored when a five- or six-membered ring is formed

Three- and four-membered rings are less easily formed Three-membered ring compounds are formed more easily than four-membered ring compounds The likelihood of the reacting groups finding each other decreases sharply when the groups are in compounds that would form seven-membered and larger rings.

Designing a synthesis …