OH- in different substances

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Hydroxide or OH^-, is a common base that's used quite often in the teaching and practical use of chemistry. It is found in many compounds and molecules but there is one thing that bothers me. So if you were to look at the formal charge of a hydroxide molecule, you'll see that there are 6 lone electrons on the oxygen with also a shared electron between the oxygen and the hydrogen. Is this specific molecule formed through the auto-ionization of water? You know where a H₂0 molecule breaks into OH^- and H⁺. It creates a proton which would make sense if it left its electron for the hydroxide. But then the appearance of OH^- in compounds is.. odd. For example in benzoic acid, a hydroxide can be found bonded to a carbon atom. In hydroxide, the oxygen has a negative formal charge so it doesn't make sense for it to form another covalent bond as it would just make it more negative. I also thought about the possibility of coordinate bonding but the carbon atom in this example compound is taking in 4 electrons from 3 different sources, one from the OH, one from one carbon, and two from another. So if there is no possibility of the OH in benzoic acid being the same as hydroxide, then what is it? Would it be simply a normal oxygen bonded to another hydrogen? which bonded to a carbon? It doesn't seem to have the same properties as hydroxide as of course, it's an acid and it donates a proton. I simply just don't understand the forming of molecules as this. My best guess is that Biology is the answer with certain organelles but I find that someone on this site would much enjoy enlightening me.

[chenbeier]

Here  you do mix something up. We speak from Hydroxide, if this is bonded to a metal like NaOH => Na+ + OH-. The electron from the sodium is given to the oxygen,. Same like you described in water H2O => H+ + OH-.

In organic compounds like alcohols, carbon acids, etc. the OH is bonded by a kovalent bond, there is no ionic charge between carbon and oxygen. The seperation takes place between Oxygen and Hydrogen. Like R-COOH => R-COO- + H+. The OH group is called Hydroxyl and the COOH group is called Carboxyl.

Edited October 9, 2018 by chenbeier