Alkoxychlorocarbenes (ROCCl, R = benzyl, cyclohexyl, and I-octyl) were generated from the corresponding diazirines in acetonitrile, dichloroethane, benzene, cyclohexane, and pentane solutions at 25 degreesC and the fragmentations of these carbenes were examined. Formation of RCl (and alkenes when R = cyclohexyl or I-octyl) occurred efficiently in all of the solvents. The rate constant for the Fragmentation of PhCH2OCCl (determined by laser flash photolysis) was similar to10(5) s(-1), and relatively independent of solvent. Photolysis of PhCH2OC(N-2)Cl in Ar matrixes led to the carbene. PhCH2OCCl, as well as its primary fragmentation products, the benzyl and COCl radicals. A prominent product was also phenacyl chloride, PhCH2COCl, a formal rearrangement product of the carbene. Computational studies of the rearrangements and fragmentations of MeOCCl, EtOCCl, and PhCH2OCCl at the DFT and coupled cluster levels afforded transition states and energetics. These studies allowed us to identify several mechanistic pathways. including concerted and homolytic processes that are predicted to prevail in nonpolar solvents and matrixes as opposed to heterolytic (ionic) processes in polar solvents. The existence of cis and trans forms of R-OC-Cl and their interconversion, are complicating factors that were considered computationally.