The entropy deficiencies of the Information Theory are used to measure the information 'distance' between the electron densities of the transition-state complex in collinear atom exchange reactions and the corresponding 'promolecular' densities obtained from electron distributions of the reaction substrates and products. These quantities are used to probe similarities between electronic structures of the transition-state complex and those of the dissociation subsystems for the forward (products) and reverse (substrates) reactions, thus providing entropic criteria of a degree of closeness of the transition-state configuration relative to substrates and products. The electronic and geometric components of such information-theoretic distances are separated and discussed. They both satisfy the qualitative implications of the Hammond postulate. (C) 2003 Elsevier Science B.V. All rights reserved.