Question

The conversion of 2R-bromo-3-methylbutane into 2S-iodo-3-methylbutane using iodide ion in DMF solution resulted in a product mixture that had an optical activity of -33 degrees. A quick look in the literature shows that pure 2R-bromo-3-methylbutane rotates plane-polarized light +66 degrees. What is the product distribution and what proportion of this reaction is occuring via SN1 and SN2 processes.