title: Systematic study on the TD-DFT calculated electronic circular dichroism spectra of chiral aromatic nitro compounds: A comparison of B3LYP and CAM-B3LYP.
abstract: B3LYP is one of the most widely used functional for the prediction of electronic circular dichroism spectra, however if the studied molecule contains aromatic nitro group computations may fail to produce reliable results. A test set of molecules of known stereochemistry were synthesized to study this phenomenon in detail. Spectra were computed by B3LYP and CAM-B3LYP functionals with 6-311++G(2d,2p) basis set. It was found that the range separated CAM-B3LYP gives better predictions than B3LYP for all test molecules. Fragment population analysis revealed that the nitro groups form highly localized molecule orbitals but the exact composition depends on the functional. CAM-B3LYP allows sufficient spatial overlap between the nitro group and distant parts of the molecule, which is necessary for the accurate description of excited states especially for charge transfer states. This phenomenon and the synthesized test molecules can be used to benchmark theoretical methods as well as to help the development of new functionals intended for spectroscopical studies.
authors.affiliation: Department of Organic Chemistry and Technology, Budapest University of Technology and Economics, Szent Gellért tér 4, Budapest 1111, Hungary. Electronic address: bkomjati@mail.bme.hu.
authors.forename: Balázs
authors.initials: B
authors.lastname: Komjáti
authors.affiliation: Department of Pharmaceutical Chemistry, Semmelweis University, Hőgyes Endre utca 7, Budapest 1092, Hungary.
authors.forename: Ákos
authors.initials: Á
authors.lastname: Urai
authors.affiliation: Department of Pharmaceutical Chemistry, Semmelweis University, Hőgyes Endre utca 7, Budapest 1092, Hungary.
authors.forename: Sándor
authors.initials: S
authors.lastname: Hosztafi
authors.affiliation: Department of Pharmaceutical Chemistry, Semmelweis University, Hőgyes Endre utca 7, Budapest 1092, Hungary.
authors.forename: József
authors.initials: J
authors.lastname: Kökösi
authors.affiliation: Department of Organic Chemistry and Technology, Budapest University of Technology and Economics, Szent Gellért tér 4, Budapest 1111, Hungary.
authors.forename: Benjámin
authors.initials: B
authors.lastname: Kováts
authors.affiliation: Department of Organic Chemistry and Technology, Budapest University of Technology and Economics, Szent Gellért tér 4, Budapest 1111, Hungary.
authors.forename: József
authors.initials: J
authors.lastname: Nagy
authors.affiliation: Department of Pharmaceutical Chemistry, Semmelweis University, Hőgyes Endre utca 7, Budapest 1092, Hungary.
authors.forename: Péter
authors.initials: P
authors.lastname: Horváth
keywords: Absolute configuration determination; CAM-B3LYP; Charge transfer; Circular dichroism; Density functional theory; Nitro group; Substituent effect