In this work, we have investigated in position (r) and momentum (p) spaces the concurrent phenomena occurring at the vicinity of the transition state (TS) (the so-called transition region) of selected chemical reactions (such as the hydrogenic abstraction and the exchange hydrogenic reactions) by means of a broad set of single information-theoretic functionals of the one-particle density (such as the disequilibrium (D), exponential entropy (L), Fisher information (I) and the power entropy (J)) and composite information-theoretic measures which includes various information planes (such as the I-D, D-L, and I-J planes) and complexities of the Fisher-Shannon and López-Mancini-Calbet (LMC) types. The analysis of the single functionals and the information planes revealed that these information-theoretical elements can identify all the chemically significant regions, not only the reactant/product regions (R/P) and the TS but also those that are not present in the energy profile, such as the bond cleavage energy region (BCER), the bond breaking/forming regions (B-B/F) and the charge transfer complex. Moreover, the analysis of the complexities shows that in position as well as in the joint (r-p) spaces, the energy profile of the abstraction reaction bears the same information-theoretical features of the LMC and FS measures. Finally, it is shown why most of the chemical features of interest (such as e.g., BCER and B-B/F) are lost in the energy profile, being only revealed when particular information-theoretical aspects of localizability (L or J), uniformity (D) and disorder (I) are considered. © 2012 Wiley Periodicals, Inc.