Local electron densities and functional groups in quantum chemistry

The connections between the quantum chemical concept of local electron dens ities and the traditional concept of functional groups of organic chemistry are explored. The Density Domain criterion of functional groups and the Ad ditive Fuzzy Density Fragmentation (AFDF) method are the tools for the cons truction of representative quantum chemical models for both local electron densities and functional groups. The applications of the method of fuzzy el ectron density partitioning of molecular electron density clouds to the des cription of the local fuzzy density contributions of functional groups are explored. The constraints implied by the recently proven "Holographic Elect ron Density Theorem" are discussed, with special emphasis on the predictabi lity of differences in the activity of functional groups of a given type lo cated within different molecular environments. The special role of symmetry and symmetry deficiency are discussed, and the deviations from local symme try, as a diagnostic tool for the assessment of the reactivity of functiona l groups are explored.