Elimination - Organic Chemistry - Lecture Slides, Slides of Organic Chemistry

Download Elimination - Organic Chemistry - Lecture Slides and more Slides Organic Chemistry in PDF only on Docsity! Polar Reaction Mechanisms Eliminations docsity.com Elimination Reaction Mechanisms • Bimolecular (E2) – Two reactants involved in the rate determining step • Unimolecular (E1) – One reactant involved in the rate determining step -OCH2CH3 CH3 C H H CH2 Br C C H3C H H H + HOCH2CH3 + Br - -OCH2CH3 CH3 C H H CH2 Br C C H3C H H H CH3 C H H CH2 Br- HOCH2CH3 docsity.com Problem • Given the information on the previous slide, which of the possible products will be the major product? • If you substitute NaOC(CH3)3 for NaOCH3, will the major product change? (If so, what will it be?) docsity.com Energetic Rationale se CH3 H--- OCH;CH3 | CH,CHSC > —H “Br H Less stable transition state resembles a disubstituted alkene. oe CHyCH;O--H Hg CHy—C==C—CH,; H More stable transition state resembles a trisubstituted alkene. CHy CH,CH2C = CHy + CH3CH,OH + Br- CH3CH,0- + CHyCH;— C— CH; 2 Methyl -butene | CH,;CH=CCH3+ CHyCH,OH + Br 2-Methyl-2-butene docsity.com Stereochemical Considerations • E1 – The intermediate carbocation is achiral (planar) – Preference for alkene stereoisomers will be solely based on their relative stabilities • E2 – Formation of the pi bond requires overlap of the orbitals that will re-hybridize from sp3 to p – This requires that the hydrogen and the leaving group be planar – Anti-periplanar arrangement (potentially chiral) is preferred docsity.com Problem • Predict the mechanism (E1 vs. E2) and the major product of the following reactions. + NaOCH3 H3C H HBr + NaOC(CH3)3 H3C H HBr H3C CH3 HBr + HOCH3 docsity.com Problem • Why does the following mixture undergo elimination rather than substitution? + 2NaI Br Br + I2 + 2NaBr docsity.com