The carboxylate anion can be viewed as a resonance hybrid of the two anionic structures,or as a conjugated system of three interacting p orbitals containing four electrons(like the allylic anion system). 0 02 The C and two oxygens are all sp'hybridized,and the remaining p orbitals create the nt MO system giving rise to the half t bond between each C and O,and the half negative charge on the end oxygens. Dicarboxylic Acids These have two dissociation constants,since they can lose two protons. HO CH2 OH OH 0 CH, malonic acid KL=1.4×10-3 anion K2=2.0×10-6 dianion +2H20 +H30t+H20 +2HO+ 2013 he K for the first dissociation and K2 for the second dissociation,which generates a dianion. K2 is always less than K(the second carboxyl group is less acidic)since it takes extra energy to overcome the second negative charge being so close to the first negative charge. Ch20 Carboxylic Acids (landscape) Page 9Ch20 Carboxylic Acids (landscape) Page 9 The carboxylate anion can be viewed as a resonance hybrid of the two anionic structures, or as a conjugated system of three interacting p orbitals containing four electrons (like the allylic anion system). The C and two oxygens are all sp2 hybridized, and the remaining p orbitals create the  MO system giving rise to the half  bond between each C and O, and the half negative charge on the end oxygens. Dicarboxylic Acids These have two dissociation constants, since they can lose two protons. Ka1 for the first dissociation and Ka2 for the second dissociation, which generates a dianion. Ka2 is always less than Ka1 (the second carboxyl group is less acidic) since it takes extra energy to overcome the second negative charge being so close to the first negative charge