Question

Can a `"C"-"C"` bond exist in a stable compound?

Answer 1

Yes it can... nearly every hydrocarbon proves that.

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In any hydrocarbon containing two or more carbons, one must have a carbon-carbon bond.

`"H"_3"C"-"CH"_3`

`"H"_3"C"-"CH"_2-"CH"_3`

etc.

In all of these, carbon bonds with itself, and forms a stable compound.

Carbon cannot, however, form a stable `"C"_2` molecule at room temperature.

Here, the MO diagram of `"C"_2` suggests a Lewis structure of:

`:stackrel(..)"C"=stackrel(..)"C":`

The formal charge on each carbon is `-2` and not `0` like it would be for a nonpolar homonuclear diatomic molecule.

Its `pi` electrons are also in separate orbitals, so the `pi` bond I drew is really artificial. In reality the `"C"_2` compound would then have two half-`pi`-bonds using perpendicular sets of orbitals, so it's not quite a regular double bond overall...