The relatively simple molecule trimethylamine N-oxide, (CH3)3NO is an oxide of trimethyl ammonium ion. It acts as a metabolite and osmolyte. It is also used as a metabolite in E.coli.

The dominant Lewis structure for (CH3)3NO presents a single bond between formal N (+) and O (?), as N fulfills the octet rule. Applying IUPAC’s ionic approximation, all electrons (by pairs, as (CH3)3NO is a closed-shell system) from the σ N?C bonds are assigned to N, while the ones from the N?O bond are assigned to the oxygen. Such an electron assignment leads to formal oxidation states of (?1) for N, (?2) for O, and (+1) for the three CH3 moieties.