Why can't electrons be transferred using hydrogen ions?


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> Recognizing how oxidation and reduction occurs is essential for analyzing and understanding biochemical reactions. Which of the following methods would **NOT** be employed in transferring electrons in biochemical reactions?
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> a) As hydrogen ions (**correct**)
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> b) Through direct combination with oxygen
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> c) Directly as electrons
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> d)As hydride ions
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My problem is that, it doesn't say *why* hydrogen ions cannot transfer electrons, also I'm not sure what "hydrogen ions" exactly mean. What if you have a hydrogen ion with 2 or 3 electrons? Why can't that be used to transfer electrons?




Firstly, $\ce{H+}$ would be called a hydrogen ion, and $\ce{H-}$ would be called a hydride ion. It would take a lot of energy to get three electrons onto a hydrogen atom, and considering that we are talking about a biological system, this just won't happen.


$\ce{H+}$ would not be employed in the transfer of electrons because it is a lone proton, and has no electrons to give. Whatever electron the hydrogen atom originally had was left behind, and the proton now exists on its own. This, I believe, should explain your homework question.


To answer *your* question, $\ce{H-}$ ions are common reducing agents in non-biological organic reactions, in the forms of substances like $\ce{NaBH4}$ and $\ce{LiAlH4}$, but these are [extremely unstable](https://www.youtube.com/watch?v=odkFRsbWLF4) in aqueous solution. 


[![NAD+->NADH](https://i.stack.imgur.com/F8zjb.png)](https://i.stack.imgur.com/F8zjb.png)


Instead, cells uses [NAD+](https://en.wikipedia.org/wiki/Nicotinamide_adenine_dinucleotide) to facilitate the transfer of electrons from biomolecules, like those used in cellular respiration, in the form of $\ce{H-}$. During the transfer, one electron from the $\ce{H-}$ is transferred to a nitrogen, and the other electron along with the proton forms a bond to a carbon directly across the ring from the nitrogen, converting NAD+ to NADH, a reaction that is readily reversible.


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