Reaction : Cis or Trans Stilbene + Br2 ----------> 1,2-dibromo-1,2-diphenylethan

Question

Reaction : Cis or Trans Stilbene + Br2 ----------> 1,2-dibromo-1,2-diphenylethane

To investigate the mechanism for the addition of bromine to Stillbene, we will use the melting point of our brominated product(s) to ascertain the mechanism.

1. Assuming that the mechanism of the bromination is the ‘bromonium ion intermediate’ with an overall ‘anti’ addition of the Bromine what product and melting point do you expect for the Trans and Cis stilbene bromination products. The products can either be the ‘Meso compound, or the Racemic mixture. For the melting points data see the lab handout.

2. Besides melting point, what other data will you be collecting?

Explanation / Answer

1. the product of bromination of

cis-stilbene ---> racemic 1,2-dibromo-1,2-diphenylethane

with product melting at 114 oC

and,

trans-stilbene ---> meso-1,2-dibromo-1,2-diphenylethane

with product melting at 242 oC

2. Besides melting point analysis by NMR would tell us If the product formed is an meso or the dl pair (racemic).

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