5.3 Organic Redox

In organic molecules, redox can be hard to see at first. Hydrogenation of alkenes is an example of redox; hydrogen is added to the alkene in the presence of a catalyst, and the hydrogen reduces the alkene while the alkene oxidizes the hydrogen. The result isn't water but an alkane. The carbon atoms of the alkene were sharing a double bond because they each had two electrons not shared with hydrogen atoms, and all they could do was double up the electrons they shared with each other. Now, they've gained two more electrons, but also two more protons. Reduction is gain, so the alkene has been reduced, in this case to an alkane.

Oxidation of alcohols to aldehydes involves subtracting two hydrogen atoms, so it's easy to see how this is the opposite of the alkene reduction. In fact, the word aldehyde is itself derived from "alcohol dehydrogenated". Oxidation of aldehydes to carboxylic acids involves the straight up insertion of an oxygen atom into the molecule. In this case, the oxygen gains electrons; while before, it had most likely been double-bonded to another oxygen atom, it is now part of an organic acid and has gained the electrons of its carbon and hydrogen neighbors.

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