The effects of electron capture on the structure of XSSX′ disulfide derivatives in which the substituents attached to the sulfur atoms have different electronegativites have been investigated at different levels of theory, namely DFT, MP2, QCISD and CASSCF/CASPT2. Although it has been generally assumed that electron attachment to disulfide derivatives leads to a systematic and significant activation of the S–S bond, our results show that this is the case only when the substituents X or X′ have low electronegativity. Otherwise, the S–S bond in the anion remains practically unperturbed and only the S–X bond is largely activated or even broken, because the extra electron occupies the σ*(S–X) rather than the σ*(S–S) antibonding orbital. Our results also show that S–S activation yields a system with a unique anion, whereas when the S–X activation is significant, two stable anionic species, stretched and bent, are formed.