Cis- and trans-isomers of butenedioic acid, also known as maleic acid cis-isomer and fumaric acid trans-isomer , are geometric isomers that differ in the spatial arrangement of their functional groups around the carbon-carbon double bond. Both isomers have the molecular formula C4H4O4 and contain a carbon-carbon double bond C=C and two carboxylic acid groups -COOH attached to the double-bonded carbons.In the cis-isomer maleic acid , both carboxylic acid groups are on the same side of the carbon-carbon double bond, whereas in the trans-isomer fumaric acid , the carboxylic acid groups are on opposite sides of the double bond. This difference in spatial arrangement leads to distinct physical and chemical properties for the two isomers.Physical properties:1. Melting point: Due to the different spatial arrangements, the intermolecular forces between the molecules in the solid state are different. Maleic acid cis-isomer has a lower melting point of about 130-139C, while fumaric acid trans-isomer has a higher melting point of about 287C. The higher melting point of fumaric acid is attributed to its more symmetrical structure, which allows for better packing and stronger intermolecular forces in the solid state.2. Solubility: Maleic acid is more soluble in water than fumaric acid due to its cis-configuration, which allows for stronger hydrogen bonding with water molecules. The trans-configuration of fumaric acid results in weaker hydrogen bonding with water, making it less soluble.Chemical properties:1. Reactivity: Maleic acid is generally more reactive than fumaric acid due to the presence of the electron-withdrawing carboxylic acid groups on the same side of the molecule in the cis-isomer. This arrangement leads to a higher electron density around the carbon-carbon double bond, making it more susceptible to reactions such as addition and hydrogenation.2. Acid strength: Maleic acid is a stronger acid than fumaric acid. The cis-configuration in maleic acid allows the carboxylic acid groups to be closer together, which facilitates the formation of an intramolecular hydrogen bond between the two groups. This stabilizes the conjugate base formed upon ionization, making it easier for maleic acid to lose a proton and act as an acid.In summary, the structural difference between cis- and trans-isomers of butenedioic acid lies in the spatial arrangement of the carboxylic acid groups around the carbon-carbon double bond. This difference significantly affects the physical and chemical properties of the isomers, including melting point, solubility, reactivity, and acid strength.