Question

What is the oxidation state of the carbon atoms in acetylene?

Answer 1

Acetylene is a quite reduced form of carbon; the carbons each have a `-I` oxidation state.

Explanation:

Note that acetylene is neutral and while we can speak of the oxidation numbers of its atoms, we cannot speak of the molecule's oxidation state.

If we break up the `C-H` bonds we get `2xxH^+`, and `{C-=C}^(2-)` (carbon is more electronegative than hydrogen, so when you (for the purposes of assigning oxidation number) break this bond you put a formal `+1` charge on hydrogen, and a formal `-1` charge of carbon.

In fact, the acetylide unit `{C-=C}^(2-)` occurs as calcium carbide, `CaC_2`, which is an important industrial feedstock.

More reduced forms of carbon include ethylene, `H_2C=CH_2`, `C^(-II)`, and the methylene unit of a carbon , `-CH_2`, `C^(-II)`. Oxidation state assignments are of course formalisms; they do not have real significance other than what we assign for them. When we break a `C-C` bond in such a process, we conceive we get `2xxC*`, i.e. neutral carbon radicals.