Mechanism

When (S)-2-bromopropanoic acid [(S)-CH3CHBrCO2H] reacts with concentrated sodium hydroxide, the product formed (after acidification) is (R)-2-hydroxypropanoic acid, commonly known as (R)-lactic acid.  This is 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, it takes place with overall retention of configuration to product (S)-2-hydroxypropanoic acid.  The mechanism of this reaction involves a phenomenom called neighboring group participation.  Write a detailed mechanism for this reaction that accounts for the net retention of detailed mechanism for this reaction that accounts for the net retention of configuration when Ag+ and a low concentration of hydroxide are used.