H3C OEt H₂C 1. NaOEt, EtOH OEt 2. H₂O* H3C EtOH OEt Esters, like aldehydes and ketones, are weakly acidic. Treatment of an ester with 1 equivalent of a strong base, such as sodium ethoxide, causes a reversible carbonyl condensation to occur that forms a f-ketoester. This reaction is known as the Claisen condensation. The tetrahedral intermediate thus formed expels an alkoxide leaving group to give an acyl substitution product, a f-ketoester. The steps leading up to this point are all reversible. The best yields for the Claisen condensation are obtained when the starting ester has more than one acidic a-hydrogen. In these cases, a second deprotonation of the x-carbon drives the reaction equilibrium toward the product, thus requiring a full equivalent of base instead of a catalytic amount. Subsequent protonation with dilute aqueous acid resultsn a high yield of the final product. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instructions 20 H3C EtO: X HH EtOH OEt H3C OEt H 7 a

H3C OEt H₂C 1. NaOEt, EtOH OEt 2. H₂O* H3C EtOH OEt Esters, like aldehydes and ketones, are weakly acidic. Treatment of an ester with 1 equivalent of a strong base, such as sodium ethoxide, causes a reversible carbonyl condensation to occur that forms a f-ketoester. This reaction is known as the Claisen condensation. The tetrahedral intermediate thus formed expels an alkoxide leaving group to give an acyl substitution product, a f-ketoester. The steps leading up to this point are all reversible. The best yields for the Claisen condensation are obtained when the starting ester has more than one acidic a-hydrogen. In these cases, a second deprotonation of the x-carbon drives the reaction equilibrium toward the product, thus requiring a full equivalent of base instead of a catalytic amount. Subsequent protonation with dilute aqueous acid resultsn a high yield of the final product. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instructions 20 H3C EtO: X HH EtOH OEt H3C OEt H 7 a

Organic Chemistry

9th Edition

ISBN:9781305080485

Author:John E. McMurry

Publisher:John E. McMurry

Chapter17: Alcohols And Phenols

Section17.2: Properties Of Alcohols And Phenols

Problem 4P: Rank the following substances in order of increasing acidity: (a) (CH3)2CHOH, HCâ‰¡CH, (CF3)2CHOH,...

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