THE PROBLEM OF DEHYDROHALOHENATION OF (S)-1-Bromo-1,2-diphenylethane with a strong base

(S)-1-Bromo-1,2-diphenylethane reacts with a strong
base to produce  a  mixture  of E and Z isomers  .
These are formed by two conformations  in which
H  and  Br are both in anti position .Only one
predominates.Product of the conformation
that is more stable.