| In polar solvents, the fragmentation mechanism of alkoxychlorocarbenes (ROCCI) depends on the R group. If R is a primary group, the carbene mainly fragments through a bimolecular SN2 mechanism, whereas if R is a tertiary group, fragmentation through an ion pair mechanism is expected. Secondary R group carbenes might fragment either way, or with competition of both pathways.; Structural effects on the fragmentation mechanisms of alkoxychlorocarbenes are further examined in this Dissertation and a Hammett study of a series of substituted benzyloxychlorocarbenes suggests that the mechanism changes from a predominantly heterolytic ion pair mechanism to a predominantly homolytic radical pair mechanism when the substituent is changed from an electron-donating group (p-Me, p-Ph) to an electron withdrawing group (m-Cl, p-CF3, p-NO2).; The significant methanol trapping of benzyloxychlorocarbene in McOH/pentane to afford benzyl alcohol raises the question of how alkoxychlorocarbenes fragment in non-polar solvents where ionic fragmentations seem unlikely. Therefore, we investigated the fragmentations of benzyl-, cyclohexyl- and n-octyloxychlorocarbenes in various solvents and found that both homolytic and concerted cleavages are responsible for the fragmentations of alkoxychlorocarbenes in nonpolar solvents.; Studies were conducted on the fragmentation of 2,2-diphenylethoxychlorocarbene and the decomposition of 2,2-diphenyldiazoethane. 2,2-Diphenylethoxychlorocarbene fragmented concertedly with 1,2-phenyl migration to afford an ion pair, leading to rearranged products (stilbenes and α-chlorobibenzyl). Small quantities of unrearranged products (2,2-diphenylethyl chloride and 1,1-diphenylethene) were also formed, probably directly from the attack of Cl− on the carbene. Similar chemistry was observed for the 2,2-diphenylethyldiazonium chloride ion pair.; Allyl and homoallyl substituted oxachlorocarbenes have not yet been investigated. In this Dissertation we examined allyloxy, allyl-1,1-d 2-oxy, 3-buten-2-oxy, trans-2-buten-1-oxy, nortricyclyloxy and exo-5-norbornen-2-oxy chlorocarbenes. In polar solvents these carbenes fragmented through the ion pair mechanism; while in non-polar solvents the concerted and radical pair reactions competed with each other. The fragmentations of nortricyclyloxy and exo-5-norbornen-2-oxy chlorocarbenes in DCE were found to proceed through distinct ion pairs, which collapsed to different distributions of nortricyclyl and norbornenyl chlorides, in contrast to the results obtained from the solvolysis of the corresponding brosylates. |
