The ultraviolet and visible absorption spectra of a number of alkyl-, cycloalkyl-, aryl-, alky nylcarbonium ions, and of hydroxy-and oxocarbonium ions, the structures of which have been established by nmr spectroscopy, are reported in fluorosulfonic acid-antimony pentafluoride and concentrated sulfuric acid (oleum) solutions, generally at low temperatures. Alkylcarbonium ions are shown to exhibit no ultraviolet absorption above 210 µ. Aryl-, cyclopropyl-, and alkynylcarbonium ions show characteristic ultraviolet absorption spectra. Alkyloxocarbonium ions show no ultraviolet absorption maxima above 210 µ, whereas aryloxocarbonium ions absorb in the characteristic aryl-conjugated regions. The ultraviolet spectra of a number of protonated ketones (hydroxycarbonium ions) were also obtained and compared to the related carbonium ions.
WE report studies which demonstrate the occurrence of ready lithium exchange between "ostensibly" organic-bound lithium of organolithium reagents and inorganic lithium of lithium ha1ides.l At room temperature the lithium-7 n.m.r. spectrum2 of a mixture of methyl-lithium and lithium bromide in tetrahydrofuran (THF) solution consists of a sharp single line having a chemical-shift value between that of pure methyllithium and pure lithium bromide.? The spectra reproduced in the Figure illustrate that this single lithium resonance line is an average value resulting from rapid lithium exchange between the organic and inorganic l i t h i ~r n , ~ for three ratios of methyllithium to lithium bromide.Exchange is sufficiently slow a t -100" for t Chemical shifts (6) are relative to external 0*5~-LiBr in THF. 6 (methyl-lithium) = +41 Hz. in THF a t A values are -100" and is of half-width (A) -3 Hz. probably accurate to f0.5 Hz.A (LiBr) < 1 Hz. 6 values are reproducible to f l Hz.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.