title: Reactivity differences between α,β-unsaturated carbonyls and hydrazones investigated by experimental and theoretical electron density and electron localizability analyses.
abstract: It is still a challenge to predict a compound's reactivity from its ground-state electronic nature although Bader-type topological analyses of the electron density (ED) and electron localizability indicator (ELI) give detailed and useful information on electron concentration and electron-pair localization, respectively. Both ED and ELI can be obtained from theoretical calculations as well as high-resolution X-ray diffraction experiments. Besides ED and ELI descriptors, the delocalization index is used here; it is likewise derived from theoretical calculations as well as from experimental X-ray results, but in the latter case, demonstrated here for the first time. We investigate α,β-unsaturated carbonyl and hydrazone compounds because resonance exhibited by these compounds in the electronic ground-state determines their reactive behavior. The degree of resonance as well as the reactivity contrast are quantified with the electronic descriptors. Moreover, competitive mesomeric substituent effects are studied using the two biologically important compounds acrolein and acrylamide. The reactivity differences predicted from the analyses are in line with the known reactivity of these compounds in organic synthesis. Hence, the capability of the ED and ELI for rationalizing and predicting different and competing substituent effects with respect to reactivity is demonstrated.
authors.affiliation: Institut für Chemie und Biochemie/Anorganische Chemie, Freie Universität Berlin, Berlin, Germany.
authors.forename: Simon
authors.initials: S
authors.lastname: Grabowsky
authors.forename: Manuela
authors.initials: M
authors.lastname: Weber
authors.forename: Dylan
authors.initials: D
authors.lastname: Jayatilaka
authors.forename: Yu-Sheng
authors.initials: YS
authors.lastname: Chen
authors.forename: Matthias T
authors.initials: MT
authors.lastname: Grabowski
authors.forename: Rainer
authors.initials: R
authors.lastname: Brehme
authors.forename: Malte
authors.initials: M
authors.lastname: Hesse
authors.forename: Tanja
authors.initials: T
authors.lastname: Schirmeister
authors.forename: Peter
authors.initials: P
authors.lastname: Luger
mesh_terms: D000447:Aldehydes / Q000138:chemical synthesis / Q000737:chemistry*; D004583:Electrons; D006835:Hydrazones / Q000138:chemical synthesis / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D011789:Quantum Theory
chemical_list: D000447:Aldehydes; D006835:Hydrazones