Write a mechanism to illustrate what will happen if the addition of bromine to

trans-cinnamic acid is syn; what do you expect the melting point of the syn
addition product to be?

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To understand what will happen if bromine is added to trans-cinnamic acid in a syn addition, let's break down the reaction mechanism and predict the melting point of the product.

1. Reaction Mechanism:
In a syn addition, both bromine atoms will add to the same side of the double bond in trans-cinnamic acid. This addition results in the formation of a new compound, namely, 2,3-dibromo-3-phenylpropanoic acid.

The mechanism involves the following steps:
a) The pi electrons of the trans-cinnamic acid double bond attack one of the bromine atoms, initiating the addition reaction.
b) The double bond breaks, and bromine adds to each carbon atom.
c) The carbonyl oxygen accepts a hydrogen atom from a water molecule to form a hydroxyl group (-OH).
d) The resulting compound, 2,3-dibromo-3-phenylpropanoic acid, is formed.

2. Predicting the Melting Point:
To predict the melting point of the syn addition product, we can consider the following factors:

a) Symmetry: The more symmetrical the compound, the higher the melting point tends to be. Since the syn addition product, 2,3-dibromo-3-phenylpropanoic acid, has a certain degree of symmetry due to the two bromine atoms on the same side of the molecule, we can expect it to have a relatively higher melting point.

b) Intermolecular Forces: The strength and nature of intermolecular forces, such as hydrogen bonding and dipole-dipole interactions, affect a compound's melting point. In the case of 2,3-dibromo-3-phenylpropanoic acid, its high molecular weight, presence of electron-rich groups (bromo and carbonyl), and potential for hydrogen bonding may contribute to higher melting point than the starting material, trans-cinnamic acid.

Therefore, we can expect the melting point of the syn addition product, 2,3-dibromo-3-phenylpropanoic acid, to be higher than the melting point of trans-cinnamic acid. However, to obtain an accurate numerical value, experimental data or further theoretical calculations would be required.