Carbonyl Condensation Reactions: Aldol Condensations and Dehydration, Study notes of Organic Chemistry

Download Carbonyl Condensation Reactions: Aldol Condensations and Dehydration and more Study notes Organic Chemistry in PDF only on Docsity! 1 Carbonyl Condensation Reactions Chapter 23 Part 1 Condensation Reactions Carbonyl compounds are both the electrophile and nucleophile in carbonyl condensation reactions Condensation Reactions A combination of an α-substitution reaction and a nucleophilic addition reaction between 2 carbonyl compounds. These carbonyl compounds include: aldehydes, ketones, esters, amides, acid anhydrides, thiol esters and nitriles. 23.1 Mechanism of Carbonyl Condensation Reactions (Base Catalyzed) Carbonyl condensation reactions utilize α-substitution steps An enolate ion adds as a nucleophile to the electrophilic acceptor 23.2 Condensations of Aldehydes and Ketones: The Aldol Reaction Acetaldehyde reacts in basic solution (NaOEt, NaOH) with another molecule of acetaldhyde The β-hydroxy aldehyde product is aldol (aldehyde + alcohol) This is a general reaction of aldehydes and ketones Aldol Mechanism: 2 Aldol Reactions The aldehyde or ketone must have an α- hydrogen Condensation products are favored for monosubstituted α-carbons. Reactants are favored for disubstituted α-carbons. Some aldol reactions with aldehydes: CH3CH2CH2CH O NaOH, H2O Butanal Some aldol reactions with ketones: Aldol condensations are not favorable for ketones. CH3CCH3 O NaOH, H2O Acetone ??? Problem: Write the structure of the aldol condensation product. Pentanal 3-Methylbutanal 2-Methylbutanal Cyclopentanone Dehydration of Aldol Products: Synthesis of Enones β-hydroxy aldehydes can yield α,β unsaturated aldehydes (conjugated enones). H O OH H+ or OH- C O + H2O Base catalyzed: Pentanal 80oC NaOH, H2O Mechanism: Dehydration Dehydration can help drive aldol reactions of ketones forward: O NaOH Cyclohexanaone Cyclohexylidenecyclohexano ne heat