1 3 r 3 4 July 8, 2019 16 32 64 128 1 3 r 4 2 (- 1 3 7 r m 3 4 1 3-dihydroxypropane & (r)-1 3 4-trihydroxy butan-2-one 1 2 r 3 3 4 3 2r 5 1 3 8 r )= 8 3 4