The intermediates of electroreduction of 3 hexyne 2,5 diol at platinized platinum electrode in perchlorate aqueous solutions with various pH values have been studied by using electrochemical ESR technique with the spin trap phenyl tert butyl nitrone. The six line spectra in the three solutions with 1.5, 3.5 and 5.0 pH values could be ascribed to the form of the radicals, such as CH 3C·HC CCH 2CH 3 , in the process of producing 3 hexyne. The four line spectra, increasing in their intensities with increase in pH values from 1.5 to 5.0, show that a 2 hydroxyalkyl radical CH 3C·(OH)CH CHCH(OH)CH 3 is formed via the interaction between the atom H and intermediates 3 hexene 2,5 diol and/or CH 3C( O)·CH CHCH(OH)CH 3. [WT5HZ]