176x Filetype PPTX File size 0.23 MB Source: www.chem.ucla.edu
Introduction Functional group pK • The acidity of organic compounds is often determined a by neighboring groups because they can help stabilizing Alkane ~50 the resulting anion (i.e., halogen, nitro, etc.) because of Ester ~25 their electronegative character or due to resonance Aldehyde/ketone ~18-20 (i.e., enolate in carbonyl compounds) Alcohol ~15-19 Nitro ~8-10 • For instance, the presence of a carbonyl group greatly increases the acidity of neighboring hydrogen atoms (a-protons) because of the resonance stabilization in the resulting enolate ion (the numbers in parentheses below are from acetone, AM1) 127.8 pm (123.5 pm) 137.4 pm (149.5 pm) • Many of the carbonyl compounds can be deprotonated with moderately strong bases i.e., hydroxide, alcoholates, etc. Aldol Condensation • Ketones and aldehydes can be reacted with each other in Aldol or Claisen-Schmidt condensation: H H - O OH T O + [OH] Aldol O O H H Ph H H Self condensation of acetaldehyde to O OH O form crotonaldehyde also called "aldol" - T + [OH] O O H Ph H Ph Formation of cinnamaldehyde Theory for the Experiment I • In Chem 14CL, acetone is reacted with two equivalents of benzaldehyde using sodium hydroxide as catalyst: O CHO O NaOH(aq.)/EtOH 2 + + 2H2O • The first step is the formation of the first enolate ion: O O O + H O C C + – 2 OH C C C C H enolate ion • Note that water is one of the products in the enolate formation the amount of water has to be minimized in order to optimize the amount of enolate in the reaction mixture. Theory for the Experiment II • The enolate ion acts as the nucleophile, which attacks the carbonyl group of the benzaldehyde to form the new C-C bond: • The trans, trans-isomer is primarily formed and isolated in the reaction. Running the Reaction • Acetone is reacted with two equivalents of benzaldehyde in a small Erlenmeyer flask. • An aqueous ethanolic solution of sodium hydroxide is added slowly (drop wise) while stirring. • The mixture is stirred for 30 minutes. • The crude product precipitates as a yellow solid from the solution during the reaction.
no reviews yet
Please Login to review.