The oxidation state of carbon in carbon monoxide is indeed . This is because oxygen contributes a to the state, and the molecule's overall charge is neutral. Although diatomic carbon with a quadruple bond is theorized by some scientists possibly to exist, it is not regularly observed. The allotropes of carbon (such as graphite and diamond) are solids, not liquids, at room temperature. Hydrogen is less electronegative than carbon, and some 6-member carbon rings (such as cyclohexane) are not aromatic.

Since carbon has four valence electrons in its shell, it can form up to four bonds with different atoms to complete its valence shell with electrons.