Investigating how electrons propagate through a single molecule is one of the missions of molecular electronics. Electrons, however, are also efficient catalysts for conducting radical reactions, a property that is often overlooked by chemists. Special attention should be paid to electron catalysis when interpreting single-molecule conductance results for the simple reason that an unexpected reaction mediated or triggered by electrons might take place in the single-molecule junction. Here, we describe a counterintuitive structure-property relationship that molecules, both linear and cyclic, employing a saturated bipyridinium-ethane backbone, display a similar conductance signature when compared to junctions formed with molecules containing conjugated bipyridinium-ethene backbones. We describe an ethane-to-ethene transformation, which proceeds in the single-molecule junction by an electron-catalyzed dehydrogenation. Electrochemically based ensemble experiments and theoretical calculations have revealed that the electrons trigger the redox process, and the electric field promotes the dehydrogenation. This finding not only demonstrates the importance of electron catalysis when interpreting experimental results, but also charts a pathway to gaining more insight into the mechanism of electrocatalytic hydrogen production at the single-molecule level.