Quantum molecular similarity. 1. BCP space

We propose a new similarity measure operating in an abstract space spanned by properties evaluated at bond critical points defined by the theory of At oms in Molecules. Consequently, we represent molecules compactly and reliab ly, extracting the relevant information from their ab initio wave function. Typical problems of continuous quantum similarity measures are thereby avo ided. The practical use of this novel method is adequately illustrated via the Hammett equation for para and meta substituted benzoic acids. On the ba sis of our definition of distances between molecules in BCP (Bond Critical Point) space, we are able to reproduce the experimental sequence of aciditi es determined by the well-known sigma constant of a set of substituted cong eners. Moreover, our approach points out where the common reactive center o f the molecules is. Due to these promising results we embark on a research program systematically addressing further issues outlined in this work. The generality and feasibility of our approach will enable predictions in medi cally related QSARs.