The reaction of (2R,3S)-3-bromo-2,3-diphenylhexane with NaNH2 in liquid NH3 yields three products: Two cis-trans isomers (A) and a pure isomer (B) . Another substance, (2S,3S)-3-bromo-2,3-diphenylhexane, under the same conditions gives a different cis-trans mixture (C) and a pure isomer (D). Determine the structures of all these products and explain why the two reactants produce two different pure isomers (B and D).