Which acid, maleic or fumaric acid appears to be more reactive to bromine addition? How does the cis/trans affect this?

To determine which acid, maleic or fumaric acid, is more reactive to bromine addition, we need to consider their chemical structures and the effect of cis/trans isomerism.

Maleic acid and fumaric acid are structural isomers, meaning they have the same molecular formula but differ in the arrangement of their atoms. Maleic acid has the cis-configuration, where the carboxylic acid groups (-COOH) are on the same side, while fumaric acid has the trans-configuration, where the carboxylic acid groups are on opposite sides.

The reactivity of these acids towards bromine addition depends on the stability of the intermediate formed during the reaction. In bromine addition, an electrophilic addition reaction occurs, where bromine adds across the double bond of the acid.

In the case of maleic acid, the two carboxylic acid groups are on the same side of the molecule, creating steric hindrance. This close proximity results in repulsion between the two groups, making the double bond more reactive towards bromine addition. Additionally, the cis-configuration allows for proper alignment of the double bond with bromine, facilitating the addition.

On the other hand, fumaric acid has the carboxylic acid groups on opposite sides due to the trans-configuration. This arrangement allows for a larger separation between the groups, reducing steric hindrance. As a result, the double bond is less reactive towards bromine addition compared to maleic acid.

In summary, maleic acid is more reactive towards bromine addition than fumaric acid. The cis-configuration of maleic acid increases the reactivity due to decreased steric hindrance and proper alignment of the double bond with bromine.