Ch. 8 - Elimination ReactionsSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins

Solution: When (S)-2-bromopropanoic acid [(S)-CH3CHBrCO2H] reacts with concentrated sodium hydroxide, the product formed (after acidification) is (R)-2-hydroxypropanoic acid [(R)-CH3CHOHCO2H, commonly known as (R)-lactic acid]. This is, of course, the normal stereochemical result for an SN2 reaction. However, when the same reaction is carried out with a low concentration of hydroxide ion in the presence of Ag2O (where Ag+ acts as a Lewis acid), it takes place with overall retention of configuration to produce (S)-2-hydroxypropanoic acid. The mechanism of this reaction involves a phenomenon called neighboring-group participation. Write a detailed mechanism for this reaction that accounts for the net retention of configuration when Ag+ and a low concentration of hydroxide are used. 

Problem

When (S)-2-bromopropanoic acid [(S)-CH3CHBrCO2H] reacts with concentrated sodium hydroxide, the product formed (after acidification) is (R)-2-hydroxypropanoic acid [(R)-CH3CHOHCO2H, commonly known as (R)-lactic acid]. This is, of course, the normal stereochemical result for an SN2 reaction. However, when the same reaction is carried out with a low concentration of hydroxide ion in the presence of Ag2O (where Ag+ acts as a Lewis acid), it takes place with overall retention of configuration to produce (S)-2-hydroxypropanoic acid. The mechanism of this reaction involves a phenomenon called neighboring-group participation. Write a detailed mechanism for this reaction that accounts for the net retention of configuration when Ag+ and a low concentration of hydroxide are used.