In a joint study involving electrochemical experiments and density functional calculations, we determined the oxidized and reduced structures of ethylene carbonate (EC), vinylene carbonate (VC), N-methyl-ε-caprolactam (Me-CL), and N-acetyl-ε-caprolactam (Ac-CL). This study reveals that the four molecules maintain their ring structures under the one-electron oxidation condition. Me-CL and Ac-CL have linear chain forms, whereas EC and VC still have ring-structures under the one-electron reduction condition. We suggest that such a collaborative study, including both experimentation and theory, is a simple and practical method for determining the structures of oxidized and reduced molecules.