# How do we determine carbon oxidation numbers in organic molecules?

Carbon has oxidation numbers from $- I V$ (cf methane, carbon is slightly more electronegative than hydrogen) to $+ I V$, as in $C {O}_{2}$. But how to determine the oxidation number in other scenarios?
When we assign oxidation numbers, the more electronegative atom gets the electrons; thus $C {H}_{4}$, ${C}^{- I V} + 4 \times {H}^{+ I}$, but if we have a $C - C$ bond, the electrons are ASSUMED to be shared by each carbon (because they have equal electronegativities). Thus in ethane, we have ${C}^{- I I I}$, and in propane, $2 \times {C}^{- I I I}$, the carbon termini in the chain, and the methylene $C {H}_{2}$ carbon is ${C}^{- I I}$. Of course these are all oxidized up to ${C}^{+ I V}$ upon combustion to give what?