Conformational properties and chiroptical spectra of lactams and thiolactams with 2-azabicyclo[2.2.1]heptane, 2- and 3-azabicyclo[3.2.1]octane skeletons |
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| Institution: | 1. Department of Chemistry, Technical University, 80-952 Gdańsk, Poland;2. Department of Chemistry, University of Gdańsk, 80-952 Gdańsk, Poland;3. Faculty of Chemistry, A. Mickiewicz University, 60-780 Poznań, Poland;1. Department of Chemistry, University of Southern California, Los Angeles, CA 90089, United States;2. Institute of Organic Chemistry, Karlsruhe Institute of Technology, Kaiserstraße 12, 76131 Karlsruhe, Germany;1. Dipartimento di Scienza e Alta Tecnologia, Università degli Studi dell’Insubria, Via Valleggio 11, 22100 Como, Italy;2. Department of Physical Chemistry, University of Málaga, 29071 Málaga, Spain;3. IPOC-Functional Polymers, Institute of Polymer Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany;4. Dipartimento di Chimica, Università degli Studi di Milano, Via Golgi 19, 20133 Milano, Italy;5. Istituto per lo Studio delle Macromolecole, Consiglio Nazionale delle Ricerche (ISMAC-CNR), Via E. Bassini 15, 20133 Milano, Italy |
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| Abstract: | The CD spectra of several bicyclic lactams and thiolactams were measured in different solvents. The concentration dependence of the spectra observed in hydrocarbon solvents was attributed to shifts in the equilibrium between monomer and hydrogen-bonded dimer forms. The CD of some compounds is characterized by unusually strong Cotton effects resulting from non-planarity of the amide bonds due to internal strain of the bicyclic skeletons. The X-ray crystallographic structures of 2a,c, 3b,d and 4a,b showed different degrees of distortion of the amide or thioamide moieties from planarity, which causes inherent chirality of the chromophores and profoundly affects the Cotton effect sign and magnitude. This distortion also restricts application of the sector rules for prediction of the n–π* CD sign, since they can be used only for compounds with planar chromophores. |
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