A Laser Flash Photolysis Study of Dibromocarbene and Bromochlorocarbene

Abstract

deca-2,4-diene (2a) produces CBr 2 and an aromatic compound. Bromochlorocarbene is produced by LFP of 10-bromo-10-chlorotricyclo[4.3.1.0 1,6 ]deca-2,4-diene (2b). The carbenes are trapped by pyridine to form ylides. The lifetimes of CBr 2 and CBrCl and their absolute reactivities toward pyridine and alkenes have been determined. The relative reactivity of CBr 2 toward alkenes determined by LFP methods is in excellent agreement with that determined previously by chemical analysis of reaction mixtures, and the rate constant data reveal that the absolute reactivity of CBrCl more closely resembles that of CBr 2 rather than that of CCl 2 .

A New Synthesis of Difluorodiazirine and the Absolute Reactivity of Difluorocarbene

“…However, CF 2 is not much less reactive toward these substrates than CCl 2 or CFCl: ( k add ) CCl 2 exceeds ( k add ) CF 2 by factors of only 5−19 for the alkenes of Table . Even the absolute rate constants for CBr 2 additions to these olefins are roughly comparable to those of CCl 2 and <100 times greater than those of CF 2 . The significantly greater stability of CF 2 over CFCl or CCl 2 (see above) seems somewhat underexpressed in its absolute reactivity toward alkenes.…”

Syntheses ofgem-Dihalocyclopropanes and Their Use in Organic Synthesis

“…Recent examples of syntheses of gem -bromochlorocyclopropane derivatives include the addition of bromochlorocarbene to styrene, , phenyl vinyl sulfide, some alkenes with halogen atoms removed from the double bond, ,,, and the bicyclic diene 24 (eq 52) …”

“Carbon Dichloride”: Dihalocarbenes Sixty Years After Hine

“…Perhaps surprisingly, CF 2 is only modestly less reactive than CCl 2 : k add for CCl 2 exceeds k add for CF 2 only by factors of 5−19 for the alkenes in Table . Note that even the absolute rate constants for CBr 2 additions to these alkenes are roughly comparable to those of CCl 2 and less than 100 times greater than those of CF 2 …”

“…Note that even the absolute rate constants for CBr 2 additions to these alkenes are roughly comparable to those of CCl 2 and less than 100 times greater than those of CF 2 . 68 The classical analysis of dihalocarbene stabilization focuses on resonance donation of halogen lone pairs to the vacant carbenic p orbital, as represented by resonance hybrid 35. Here, F is more effective than Cl in resonance donation because the 2p-2p overlap of F-C is superior to the 3p-2p overlap of Cl-C.…”