The H-2/D-2 switching experiments showed that there is an inverse isotope effect during iron catalyzed Fischer-Tropsch (FT) reactions. The rate of hydrocarbon production (r) increased when syngas CO/H-2 was switched to CO/D-2 with the ratio of r(H)/r(D) being 0.55-0.58. The inverse isotope effect in every propagation step was calculated to be 0.88, which is a reasonable value for an inverse isotope effect at 270 degrees C that originates from the C-H (D) bond hybridization change from sp(2) to sp(3). These results are similar to cobalt catalyzed FT reactions that were explained by the modified alkylidene mechanism by which 1-alkenes and n-alkanes are the primary products of the FT reaction and the others are products of secondary. The detailed analysis of products produced during iron catalyzed FT reactions with CO/H-2 or CO/D-2 as the syngas feeds showed that while the ratios of [1-alkenes](H)/[1-alkenes]D are less than 1, the ratios of [2-alkenes](H)/[2-alkenes]D are more than I; this indicates that 2-alkenes are produced through a pathway that is different from 1-alkenes. These results also suggest that there is a normal isotope effect during the formation of 2-alkenes through the corresponding 1-alkenes, which will result in the ratio of [1-alkenes](H)/[1-alkenes]D being less than 1. The formation of 2-alkenes is explained by the alkylidene mechanism. (C) 2014 Elsevier B.V. All rights reserved.