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?

To understand what happens when bromine is added to trans-cinnamic acid in a syn addition, we need to examine the reaction mechanism. Here is a step-by-step explanation:

1. The first step is the nucleophilic attack of the bromine molecule on the π bond of trans-cinnamic acid. This results in the formation of a cyclic bromonium ion intermediate.

2. In the second step, a bromide ion acts as a nucleophile and attacks the cyclic bromonium ion from the back side, causing ring-opening and forming a diastereomeric mixture of products.

3. In the last step, the diastereomeric mixture undergoes deprotonation to yield the final product. The syn addition refers to both bromine atoms being added to the same side of the double bond, resulting in a cis product.

Now, let's discuss the expected melting point of the syn addition product. The melting point of a compound is determined by various factors such as molecular weight, molecular symmetry, intermolecular forces, and crystal lattice structure.

In the case of the syn addition product of bromine to trans-cinnamic acid, the presence of the bromine atoms on the same side of the double bond leads to increased molecular symmetry. This symmetry reduces the polarity of the molecule, as the two bromine atoms have opposing electronegativity effects. As a result, the intermolecular forces, specifically dipole-dipole interactions, are weakened.

Weaker intermolecular forces usually result in lower melting points because the molecules are less strongly attracted to each other in the solid state. Therefore, we can expect that the syn addition product of bromine to trans-cinnamic acid will have a lower melting point compared to the starting materials.

It is worth noting that other factors, such as the presence of functional groups or substituents, can also influence the melting point. Therefore, a more accurate prediction could be made by considering the specific compound's structure and analyzing similar compounds with known melting points.