Oxygen can form 2pπ−2pπ multiple bond with itself due to its small size while sulphur cannot form multiple bond with itself as 3pπ−3pπ bond will be unstable due to large size of sulphur, but sulphur can form multiple bond with small size atom like C and N. eg. S=C=S S=C=N−↔S⊖−C≡N