Sulfites or sulphites are compounds that contain the sulfite ion SO32. The sulfite ion is the conjugate base of bisulfite. Although its acid (sulfurous acid) is elusive, its salts are widely used.
Sulfites are substances that naturally occur in some foods and the human body. They are also used as regulated food additives.
Structure
The structure of the sulfite anion can be described with three equivalent resonance structures. In each resonance structure, the sulfur atom is double-bonded to one oxygen atom with a formal charge of zero (neutral), and sulfur is singly bonded to the other two oxygen atoms, which each carry a formal charge of −1, together accounting for the −2 charge on the anion. There is also a non-bonded lone pair on the sulfur, so the structure predicted by VSEPR theory is trigonal pyramidal, as in ammonia (NH3). In the hybrid resonance structure, the S-O bonds are equivalently of bond order one and one-third.