5. Sodium acetylide (H-CC:-Na+) reacts with (R)-2-bromobutane to give (S)-3-methyl1-pentyne. Does the reaction go with retention or inversion of

5. Sodium acetylide (H-CC:-Na+) reacts with (R)-2-bromobutane to give (S)-3-methyl1-pentyne. Does the reaction go with retention or inversion of configuration? We can then assign the stereochemistry of the product as S, so the reaction goes with inversion of configuration. (b) In the Finkelstein modification potassium iodide KI is added to the reaction. The reaction proceeds 1000 times faster, and goes with retention of configuration. Why?