CHEM 211 Lecture Notes - Lecture 29: Dehydrogenation, Alcohol, Alkene
19 Nov 2016
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Document Summary
Use of elevated temperature can favor the elimination because of entropic difference. Determining substitution vs elimination: substitution and elimination compete with each other. Primary substrate: with a strong base, sn2 is favored. Secondary substrate: with a strong base, e2 is favored, weak base, sn2 is favored. Tertiary substrate: with a strong base, e2 is favored, weak base, sn1, increasing temperature favors elimination reactions, size of base impacts. Acid-catalyzed dehydration the elimination of oh: when alcohols undergo dehydrogenation to from an alkene when heated with a strong acid, primary alcohols are the most dif cult to dehydrate. Needs 180 c and 100% sulfuric acid: secondary alcohols are easier. 85% acid, 160-170 c: tertiary alcohol are very easy. Rearrangements: tertiary oh = e1, primary oh = e2. Migration can occur: migration of methyls, migration of hydrides, migration helps stabilize very unstable carbocations, forms a more stable cation, ring expansion, sometimes carbons in a ring will migrate, expanding rings into different from.
