Question

Why maleic acid is more acidic than fumaric acid, on the basis of dipole moment

Answer 1

Maleic acid or cis- butenedioic acid, being a cis- isomer is capable of forming intra-hydrogen bond after losing H+ ion, making the conjugate Base (negative ion) much stable than the trans form (Fumaric acid) because both the oxygen atoms have strong interaction with the remaining H atom.

Consider the reaction,

Ha + H2O <=>H3O+ + A-

If the conjugate Base is being more stable, equilibrium shifts mainly to the right to provide more H+ ions, and thus increases the rate of reaction.

However, fumaric acid would not have this stabilisation and thus less H+ ion is produced.

Hope this helps u!