The citrate anion of trisodium citrate has three carboxylate groups. I am concerned with whether or not there will be hydrogen bonding in water, with hydroxyl groups of other ions or alcohols.

  1. It has been suggested to me that the negative carboxylate oxygens won't hydrogen bond, due to resonance delocalisation of the charge. If it mattered whether or not the oxygen was partially charged, I would hypothesize that the oxygen is charged, because carbon has a lower electronegativity.

  2. The oxygen should have two lone pairs, yet it has either been implied that they are not there, or for some reason that they will not interact in hydrogen bonding.

My question is: will the citrate anion hydrogen bond with other molecules or polymers with hydroxyl groups, in aqueous solution?

It has been made aware to me that there is an article that has done research to show that carboxylates are strong hydrogen bond acceptors in anhydrous solvents.

  • $\begingroup$ Yes it will form hydrogen bonds all right. Indeed, oxygen has some lone pairs, they are very much there and won't go anywhere, even if it were not charged (though in fact it is charged, which makes hydrogen bonding all the more effective). $\endgroup$ – Ivan Neretin Jan 31 '18 at 7:54
  • $\begingroup$ @IvanNeretin I completely agree. It will hydrogen bond for sure. I think that it will form hydrogen bonds even if it is chelating some ion (calcium or something like that) $\endgroup$ – Raoul Kessels Jan 31 '18 at 9:48

As the comments indicate, you don't need a formal charge on oxygen at all. "Neutral" oxygen atoms are usually negatively charged anyway just from bond polarity, as in water. That and the lone pairs on oxygen are quite enough to enable hydrogen bonds to protic hydrogen.


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