Laser Flash Photolysis Study of Alkylhalocarbenes Generated from Non-Nitrogenous Precursors

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 1998-02, Vol.102 (9), p.1507-1513
• Main Authors: Robert, Marc, Likhotvorik, Igor, Platz, Matthew S, Abbot, Sarah C, Johnson, Richard
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp972464y

Previously we have studied the photochemistry of alkylchlorodiazirines using laser flash photolysis methods and the pyridine ylide technique (White et al. J. Org. Chem. 1992, 17, 2841). The yield of trappable carbene was found to be a sensitive function of the alkylcarbene structure. This was attributed to ring opening of the diazirine to form a biradical which could suffer rearrangement, in addition to fragmentation to a carbene. It was also possible to explain the data in terms of a carbene−pyridine complex which can either rearrange or collapse to an ylide. In this work, alkylchlorocarbenes are generated from phenanthridenes. The results do not rule out the intermediacy of a carbene−pyridine complex; however, if this species is formed, it does not rearrange to chloroalkene in competition with collapse to form an ylide. This study reduces the urgency with which to postulate carbene−olefin complexes (Tomioka et al. J. Am. Chem. Soc. 1984, 106, 454).