Winter Arthur H, Gibson Harry H, Falvey Daniel E
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20740, USA.
J Org Chem. 2007 Oct 26;72(22):8186-95. doi: 10.1021/jo0708184. Epub 2007 Sep 25.
Laser flash photolysis of 1-(carbazol-9-yl)-2,4,6-trimethylpyridinium tetrafluoroborate generates the carbazolyl nitrenium ion (tau = 333 ns, kobs = 3.0 x 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.
对1-(咔唑-9-基)-2,4,6-三甲基吡啶四氟硼酸盐进行激光闪光光解，会生成咔唑基氮鎓离子（τ = 333纳秒，kobs = 3.0×106 M-1s-1），该离子在乙腈中的吸收带位于570和620纳米处。已发现该氮鎓离子的反应活性与结构相似的闭壳二芳基氮鎓离子相当，但光谱证据支持将观察到的氮鎓离子归为开壳单线态双自由基。咔唑基氮鎓离子的反应活性也比二芳基氮鎓离子更高，这可能是由于其具有反芳香性。通过分析优化的几何结构、核独立化学位移和等键反应，进行了从头算和杂化密度泛函理论计算，以研究该氮鎓离子及类似氮鎓离子的反芳香性程度。
