biostudies-literatureUnknown16(9)Mandigo JAQuantitative appreciation of electronic substituent effects is beneficial across the chemical sciences, from reaction kinetics and catalysis to functional materials design and enzymatic processes. While Hammett parameters (<i>σ</i> constants) constitute the most widely invoked paradigm, their determination for structurally complex functional groups is often impractical by traditional empirical means. Herein, we demonstrate that the reversible one-step, 2-e^- reduction of linearly functionalized 1,1',3,3'-tetraethoxycarbonyl-6,6'-biazulene provides a simple electrochemical readout of effective Hammett constants. By design, the values obtained align closely with the conventional <i>σ</i> _p descriptors pertaining to benzenoid systems. This approach not only helps reevaluaRSC advances8371-8379https://www.ebi.ac.uk/biostudies/studies/S-EPMC12893891biostudies-literature6,6'-Biazulenic core as a platform for unlocking Hammett constants &lt;i&gt;via&lt;/i&gt; electrochemical free-energy relationships.PMC12893891Mandigo JAKelsey SRBarybin MVSabala RCDairo MKWeghorn CRBerrie CLApplegate JCFair RJanzen DEThompson WHfalse6,6'-Biazulenic core as a platform for unlocking Hammett constants &lt;i&gt;via&lt;/i&gt; electrochemical free-energy relationships.Quantitative appreciation of electronic substituent effects is beneficial across the chemical sciences, from reaction kinetics and catalysis to functional materials design and enzymatic processes. While Hammett parameters (<i>σ</i> constants) constitute the most widely invoked paradigm, their determination for structurally complex functional groups is often impractical by traditional empirical means. Herein, we demonstrate that the reversible one-step, 2-e^- reduction of linearly functionalized 1,1',3,3'-tetraethoxycarbonyl-6,6'-biazulene provides a simple electrochemical readout of effective Hammett constants. By design, the values obtained align closely with the conventional <i>σ</i> _p descriptors pertaining to benzenoid systems. This approach not only helps reevalua2026-01-01T00:00:00Z2026 Feb2026-07-15T17:28:52.867Z2026-07-07T03:08:46.659ZS-EPMC128938914169409710.1039/d6ra00120c