Arrange the following compounds in decreasing order of their acidic strength (consider the first ionization constant, K_ a1 , for the dicarboxylic acids): (i) (ii) (iii) (iv)

Step-by-step solution

The given compounds are: (i) Maleic acid (cis-butenedioic acid) (ii) Fumaric acid (trans-butenedioic acid) (iii) Crotonic acid (trans-but-2-enoic acid) (iv) Acrylic acid (prop-2-enoic acid) To determine the acidic strength, we compare the stability of their conjugate bases: 1. Maleic acid (i) vs Fumaric acid (ii): After losing the first proton, the conjugate base of maleic acid (hydrogen maleate ion) is highly stabilized by intramolecular hydrogen bonding between the cis-carboxylate and carboxylic acid groups. This