Carbazolyl Nitrenium Ion:  Electron Configuration and Antiaromaticity Assessed by Laser Flash Photolysis, Trapping Rate Constants, Product Analysis, and Computational Studies

Laser flash photolysis of 1-(carbazol-9-yl)-2,4,6-trimethylpyridinium tetrafluoroborate generates the carbazolyl nitrenium ion (τ = 333 ns, k obs = 3.0 × 106 M-1s-1) having absorption bands at 570 and 620 nm in CH3CN. The nitrenium ion is found to have reactivity comparable to structurally similar c...

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Bibliographic Details
Published in:Journal of organic chemistry 2007-10, Vol.72 (22), p.8186-8195
Main Authors: Winter, Arthur H, Gibson, Harry H, Falvey, Daniel E
Format: Article
Language:English
Subjects:
Chemical reactivity
Chemistry
Exact sciences and technology
Heterocyclic compounds
Heterocyclic compounds with only one n hetero atom and condensed derivatives
Organic chemistry
Preparations and properties
Reactivity and mechanisms
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Summary:Laser flash photolysis of 1-(carbazol-9-yl)-2,4,6-trimethylpyridinium tetrafluoroborate generates the carbazolyl nitrenium ion (τ = 333 ns, k obs = 3.0 × 106 M-1s-1) having absorption bands at 570 and 620 nm in CH3CN. The nitrenium ion is found to have reactivity comparable to structurally similar closed-shell diarylnitrenium ions, but spectroscopic evidence favors an open-shell singlet diradical assignment for the observed nitrenium ion. The carbazolyl nitrenium ion is also more reactive than diarylnitrenium ions as a likely result of antiaromatic character. Ab initio and hybrid DFT calculations were performed to address the degree of antiaromaticity in this and similar nitrenium ions through analysis of optimized geometries, nucleus independent chemical shifts, and isodesmic reactions.
ISSN:0022-3263
1520-6904
DOI:10.1021/jo0708184