One way to deconstruct the stereochemistry of the proposed reaction in exercise 2.3 on paper (HA case) 1) Convert original Fischer structure back into equivalent 3D projection A to leave 2) Re-draw 3D projection so that the line of attack by reagent is on plane of page and on horizontal A to leave

Inverted product (HA gone) One way to deconstruct the stereochemistry of the proposed reaction in exercise 2.3 (cont.) 3a) Bring in attacking Cl* along horizontal and deform the molecule consistent with the expected inversion 5-coordinate- activated complex 3b) Finish reaction by completing inversion and ejecting HA . Inverted product (HA gone)

R y x z Turn 180o in plane, reversing H with Br, OH with Cl One way to deconstruct the stereochemistry of the proposed reaction in exercise 2.3 (cont.) 4) Rotate projection so that Fischer orientation is maintained, and, so that smallest group is on top along the vertical. In the case below, the entire molecule rotates 180o along the x-y plane to switch Br with H, keeping H and Br behind that plane. y x z 5) Re-draw Fischer projection and assign Turn 180o in plane, reversing H with Br, OH with Cl R 16 35.4 80

Questions ? Try second part of Exercise 2.3 (Replace HB and determine R,S of product …show work and turn in (mol $)