The determination of reactivity parameters for short-lived intermediates provides an indispensable tool for synthetic design. Despite that electrophilicity parameters have now been established for more than 250 reactive species, the corresponding parameters for benzyne and related intermediates have not been uncovered. We report a study that has allowed for the quantification of benzyne's electrophilicity parameter. Our approach relies on the strategic use of the diffusion -clock method and also provides electrophilicity parameters E for other substituted arynes.