Variations of the effective activation energy (E-alpha) throughout the glass transition were determined for 1,2-propanediamine (12PDA) and 1,2-propanediol (12PDO) by applying an isoconversional method to differential scanning calorimetry (DSC) data. E-alpha, was found to markedly decrease throughout the glass transition of 12PDA, whereas such drastic change in E-alpha, was not observed for 12PDO. Although the two simple liquids are similar in molecular structure and size, their trends in E-alpha, and fragility m throughout the glass transition can be quite different. The significant disparity in the kinetic parameters can be caused by differences in hydrogen-bonding structure between 12PDA and 12PDO. (C) 2016 Elsevier B.V. All rights reserved.