I was reading a textbook on organic chemistry and was told that carboxylate group is electron donating, but I honestly do not see how it is electron donating. Can someone kindly shed some light on this issue.
The word by word quotation is as follow:
"It can be seen that the difference between the first and second pKa values diminishes as the number of methylene groups separating the carboxyls increases,i.e. it becomes easier to lose the second proton as the other functional group is located further away. It can also be seen that since malonic acid is a stronger acid than acetic acid, then the extra carboxyl is an electron-withdrawing substituent that is stabilizing the conjugate base. Again, this effect diminishes rapidly as the chain length increases, as anticipated for an inductive effect. Of course, ionization of a carboxylic acid group to a carboxylate anion reverses the inductive effect, in that the carboxylate will be electron donating, and will destabilize the dianion.
This is reflected in the pKa2 values for malonic, succinic and glutaric acids all being larger than the pKa for acetic acid. Oxalic acid appears anomalous
in this respect, and this appears to be a result of the high charge density associated with the dianion and subsequent solvation effects." (Dewick, 2006)
Dewick, P. M. (2006). Essentials of organic chemistry: For students of pharmacy, medicinal chemistry and biological chemistry. Chichester, West Sussex, England: J. Wiley.