A solution of pure (S)-2-iodobutane ([a] = + 15.90( in acetone is allowed to react with radioactive iodide, 131I ̄, until 1.0% of the iodobutane contains radioactive iodine. The specific rotation of this recovered iodobutane is found to be + 15.58(.
(a) Determine the percentages of (R)- and (S)-2-iodobutane in the product mixture.
(b) What does this result suggest about the mechanism of the reaction of 2-iodobutane with iodide ion?