Question

What stereochemistry do you expect for the alkene obtained by E2 elimination of (1R,2R)-1,2-dibromo-1,2-diphenylethane? Draw a Newman projection of the reacting conformation.

Answer 1

Z-isomer of the alkene is formed.

Step-by-step explanation:

E2 elimination occurs in the presence of a strong base. It is a bimolecular elimination reaction in which the rate depends both on the concentration of the alkyl halide and the base.

The elimination reaction occurs in a single step. For E2 to happen, Hydrogen at the α-C and the halogen must be anti periplanar to each other or the angle between them is equals to 180°.

The reaction of (1R,2R) -1,2-dibromo-1,2-diphenylethane with a strong base gives (Z)-1-bromo-1,2-diphenylethene. The mechanism is shown in image one. Z-isomer of the alkene is formed.

The Newman projection of the reacting conformation is shown in image 2.