Sulfoxides feature relatively short S–O distances.  In DMSO, the S–O distance is 1.531 Å.  The sulfur center is pyramidal; the sum of the angles at sulfur is about 306°.
Sulfoxides are generally represented with the structural formula R−S(=O)−R, where R and R are organic groups.  The bond between the sulfur and oxygen atoms is intermediate of a dative bond and a polarized double bond. The double-bond resonance form implies 10 electrons around sulfur (10-S-3 in N-X-L notation).  The double-bond character of the S−O bond may be accounted for by donation of electron density into C−S antibonding orbitals ("no-bond" resonance forms in valence-bond language).  Nevertheless, due to its simplicity and lack of ambiguity, the IUPAC recommends use of the expanded octet double-bond structure to depict sulfoxides, rather than the dipolar structure or structures that invoke "no-bond" resonance contributors.  The S–O interaction has an electrostatic aspect, resulting in significant dipolar character, with negative charge centered on oxygen.