The electronic spectra and electronic structures of the benzyl cation and its methyl derivatives |
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| Affiliation: | 1. Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, China;2. Department of Biomolecular Systems, Max Planck Institute of Colloids and Interfaces, Potsdam 14476, Germany;3. Wuxi School of Medicine, Jiangnan University, Wuxi 214122, China;1. Institute of Geosciences IGEO (CSIC,UCM), c/Doctor Severo Ochoa, 7, 28040 Madrid, Spain;2. Middle East Technical University, Department of Civil Engineering, 06800 Ankara, Turkey;1. Key Laboratory for Large-Format Battery Materials and System, Ministry Education, School of Chemistry & Chemical Engineering, Huazhong University of Science & Technology, Luoyu Road 1037, Wuhan, 430074, PR China;2. State Key Laboratory of Crop Stress Biology in Arid Areas and College of Science, Northwest A&F University, Yangling, Shaanxi, 712100, PR China;1. Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan;2. PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan;3. Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan;4. CREST, Japan Agency for Medicinal Research and Development, 1-7-1 Otemachi, Chiyoda-ku, Tokyo 100-0004, Japan;1. Key Laboratory for Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China;2. School of Chemical Science, University of Chinese Academy of Sciences, Beijing, 100049, China;3. Center of Basic Molecular Science, Department of Chemistry, Tsinghua University, Beijing, 100084 China |
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| Abstract: | The electronic absorption spectra and NMR spectra of the benzyl cation and its methyl-derivatives were measured at room temperature and also at low temperatures. The π-electronic structure of the benzyl cation was studied theoretically by a method combining Roothaan's LCAO-SCF procedure with Pariser-Parr's approximation. The configuration interaction was considered for both singly and doubly excited configurations. Furthermore, concerning methyl substituted benzyl cation, the hyperconjugation effect of methyl groups was taken into account by the configurational interaction among the ground, charge-transfer and locally excited configurations.From these experimental and theoretical studies, it was concluded that the electronic absorption spectra of the α,α-dimethylbenzyl-,α,α,2,4,6-pentamethylbenzyl-,2,4,6-trimethylbenzyl- and 2,3,4,5,6-pentamethylbenzyl-cations commonly show two absorption peaks in 300 and 400 mμ regions. These two bands were shown to be the intramolecular charge-transfer bands which are accompanied by a great amount of electron-transfer from the occupied orbitals of the benzene ring to the 2pπ orbital of the carbon atom of the CH2 or C(CH3)2 group. The observed absorption intensity of the shorter wavelength band was found to be six or seven times stronger than that of the longer wavelength band, completely satisfying the present theoretical expectation. The benzyl and α-methylbenzyl cations were found to be unstable even at low temperature and their spectra could not be observed. |
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