Three resonance forms can be written for formic acid. 0 Q 0- H-C-O-H →H-C0H H-CtO-H major minor very minor The second structure requires the C-O-H bonds to be co-planar. One of the unshared lone pairs of oxygen is delocalized into the electrophilic system of the carbonyl group (One of the lone pairs on the hydroxyl oxygen is conjugated with the C=O double bond). Acidity Carboxylic acids can dissociate in aqueous solution into carboxylate ions and protons The equilibrium constant for this process is Ka,and more frequently we talk in terms of pK O-H+H,OR -0-+H,0 K= [R一CO2]H,O [R-CO,H] pK -l0g10 K Ch20 Carboxylic Acids (landscape) Page 6 Ch20 Carboxylic Acids (landscape) Page 6 Three resonance forms can be written for formic acid. The second structure requires the C-O-H bonds to be co-planar. One of the unshared lone pairs of oxygen is delocalized into the electrophilic  system of the carbonyl group. (One of the lone pairs on the hydroxyl oxygen is conjugated with the C=O double bond). Acidity Carboxylic acids can dissociate in aqueous solution into carboxylate ions and protons. The equilibrium constant for this process is Ka , and more frequently we talk in terms of pKa . H C O O H H C O O- H H C O O- H + + major minor very minor