In quantum mechanics, molecular systems are holistic entities whose properties can only be fully understood by studying their complete structures. However, a reductionist approach that considers a molecular structure as a sum of multiple substructures has proven useful. A prominent example is the concept of functional groups (FG), which allows an assessment of molecular reactivity or toxicity based on specific FG occurrence. The concept is important for nomenclature generation, spectroscopy, combinatorial chemistry, or drug development as well .