Photochemistry of alkyl halides. 11. Competing reaction via carbene and carbocationic intermediates

Abstract

resulting reddish-brown residue was dissolved in ethyl ether/ petroleum ether (1:9, 2 mL) and chromatographed on alumina (activity 3, 5 g) using ethyl ether/petroleum ether (1:9) as eluent. Two distinct orange bands were observed. The faster moving, more intense band yielded a fraction containing the exo compound 46 (0.0023 g, 42%), while the slower band contained the endo complex 47 (0.0009 g, 16%).Complex 46: red crystals; mp 210-212 °C; Rf 0.47, ethyl ether/ methanol /hexane (3:1:6) as eluent; IR (thin film) 2967,1609,

Photochemistry of Racemic and Resolved 2-Iodooctane. Effect of Solvent Polarity and Viscosity on the Chemistry

“…This is consistent with the photoreaction yielding a small amount of the 2-octyl carbene (Scheme ). This result has precedent in Kropp's study of the photochemistry of alkyl halides, where carbenes are often observed . Once formed the carbene could abstract hydrogen from the solvent to form octane or isomerize to ( E )- and ( Z )-2-octene, all with no deuterium.…”

The photoinduced reaction of 2‐iodothiophene in solutions of n‐heptane, dichloromethane and methanol

“…In the photolysis of 1‐bromo and 1‐iodo‐1‐hexynes in polar and nonpolar solvents, only radical‐derived products were obtained,7 contrary to the previously reported on alkyl and vinyl halides 2–4…”

“…The photoinduced reaction of organic halides, in particular iodides, has been widely studied, as well as the reactions involving the respective bromides and chlorides but to a lesser extent 1. Studies made by Kropp and co‐workers2, 3 and Taniguchi and co‐workers4 have shown that alkyl and vinyl halides, particularly iodides, in polar solvents give products which are formed both from the radical obtained in the primary process and from the carbocation produced by electron transfer in the radical pair originally formed. However, there have been differences observed between the behaviour of organic iodides and bromides.…”

Photoactivation of distal functional groups in polyfunctional molecules

“…The generation of such ~hot" cations has been demonstrated in the direct photolysis of alkyl bromides and iodides [67], and in fact 32 was independently prepared by the photolysis of an alkaline methanolic solution of 2-benzonorbornenone tosylhydrazone (conditions known to produce "hot" carbocations eia decomposition of an intermediate diazonium ion [68]). Alkene formation is also characteristic of the ~hot" ions formed by photolysis of alkyl halides [67], so that the benzonorbornadiene generated in both the aryl chloride and mesylate photolyses may likewise be attributed to this precursor (elimination in ground state solvolyses of benzonorbenenyl derivatives is generally quite minor [69]; there is a possibility that photoly~dc generation of a carbene contributes to the formation of alkene [70]. There is further support for formation of a ghot" carbocation from studies with benzobicyclo[2.2.2] den'vatives (see below).…”