期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 14, 期 15, 页码 4711-4718出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.200701926
关键词
cyclopropenylidenes; density functional calculations; singlet-triplet energy separation; substituent effects; triafulvalenes
资金
- NIGMS NIH HHS [R01 GM 68825, R01 GM068825, R01 GM068825-01A2] Funding Source: Medline
- NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES [R01GM068825] Funding Source: NIH RePORTER
Cyclopropenylidenes are Huckel aromatic pi systems in which one of the ring atoms is a carbene center. Quantum chemical calculations at the density functional level of theory, supplemented by coupled-cluster calculations, indicate that there is a sizeable energy separation between the lowest-energy singlet and triplet states of these species. Amino groups considerably increase the energy difference between these two states, whereas electron-withdrawing substituents decrease it. The 1,1-dimerization products of cyclopropenylidenes, namely, triafulvalenes, have been investigated. The calculations show that, without steric hindrance and considerable electronic stabilization, cyclopropenylidenes are kinetically unstable and dimerize. Different substituents (alkyl, sityl, terphenyl, amino, and phosphoraneiminato) were probed to tune the frontier orbital energies of cyclopropenylidenes. Accordingly, it is predicted that by a suitable choice of substituents at the olefinic positions, cyclopropenylidenes can be more nucleophilic than their five-membered ring congeners, namely, imidazol-2-ylidenes.
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