CH 221 1st Edition Lecture 26Outline of Last Lecture I. Elimination ReactionsII. E2 ReactionsIII. E1 Reactions Outline of Current Lecture IV. Anti-EliminationV. E2 and E1 ReactionsVI. Alkyl Halides in SN2 and E2 ReactionsVII.SN2 and E2 ConditionsVIII.SN1 and E1 ConditionsCurrent LectureIV. Anti-Elimination is preferred- Regunis molecule to be in a staggered conformation- Back-side attack achieves the best overlap of interacting orbitals- Avoids repulsion of electron rich base with electron rich leaving group- The alkene with the bulkiest groups on opposite sides of the double bond will be formedin greater yield because it is the most stable alkene- The more stable product is easier to form- E1 alkene forms more easilyV. E2 and E1 reactions are regioselective- Form two compounds, one in higher yield than the other- When only 1 hydrogen is bonded to the beta carbon, the major product of the E2 reaction depends on structure of alkenes- E2 elimination from 6-membered rings- Groups eliminated must both be in axial positions- E1 elimination from 6-membered rings- The H and Cl do not need to be in axial positions because the reaction isn’t concertedVI. Alkyl Halides in SN2 and E2 reactions- Nucleophile attacks carbon and forms substitution productThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- In a SN2 reaction: 1º> 2º> 3º- In a E2 reaction: 3º> 2º> 1º- Hinder SN2/E2 conditions primary alkyl halide= primary substitution- Steric hindrance favors eliminationVII. Under SN2/E2 conditions- Secondary alkyl halide=substitution(favored by weak base) and elimination(favored by strong base)- Bulky bases are used to encourage elimination- DBN: 1,5-diazabicyclo[4.3.0]non-5-ene- DBU: 1,8-diazabicyclo[5.4.0]undec-7-ene- High temperature reactions favor elimination because they have a greater ∆SVIII. Under SN1/E1 conditions- Tertiary alkyl halides under substitution and elimination- William Ether synthesis: a SN2 reaction- R-Br alkyl halide
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