Good job! More Hydrogen bonding.

The effect of a cis- versus trans- configuration in maleic and fumaric acid respectively results in different physical chemical prosperities, such as melting and boiling points. Experimentally fumaric acid exhibits a melting point (287 °C) versus maleic acid (138–139 °C).

When determining the melting point of an organic compound it is important to understand how the compound binds to itself. Melting and boiling are processes in which noncovalent interactions between molecules are disrupted. The strong the noncovalent interaction, the more energy is requiring to break them apart (e.g., more heat).

When comparing organic molecules there are several trends to consider.

1. Size of carbon chain: For a molecule with a given functional group, the melting and boiling pair increase with molecular weight. The more carbons and hydrogen mean a greater surface area possible for van der Waals interaction, thus higher melting point and boiling point.

2. The force of attraction between the molecule: The strength of intermolecular dipole-dipole, and iconic interactions is reflected in the melting and boiling point.

The higher melting point in fumaric acid (compare to maleic acid) arises because each fumaric acid molecule can hydrogen bond to multiple partners. Therefore, requiring more energy to break them apart for the melting point transition to occur.

The cis-diacid group of maleic acid enables strong hydrogen bonding corresponding to one intramolecular H-bond per molecule and either two or three intermolecular H-bonds.

In contrast, fumaric acid’s trans- configuration permits stronger intermolecular hydrogen bonding corresponding up to eight potential H-bonds per molecule.

Tallon M.A. (2016) Reactions Involving Maleic Anhydride. In: Musa O. (eds) Handbook of Maleic Anhydride Based Materials. Springer, Cham. https://doi.org/10.1007/978-3-319-29454-4_2