Carbocations

Efficient Desorption and Capture of Reactive Carbocations from Positively Charged Glass Surface Bombarded with High-Speed Water Microdroplets

“…Thus, four different types of shortlived carbocations, (a) tert-butyl (1, tertiary carbocation), (b) 2-norbornyl (2, nonclassical carbocation), (c) adamantly (3, bridgehead carbocation), and (d) benzylic (4) carbocations, were generated as intermediates in the corresponding model reaction (Figure 3). The lifetime of these carbocations ranges from nanoseconds to picoseconds, 3 as estimated previously by laser flash photolysis, azide clocks, and theoretical calculations, which we also discussed in detail in our earlier report. 25−30 We sampled the reaction aliquot at 5 min after initiating the reaction, followed by dispensing it on different surfaces and bombarding it with water microdroplets (Figure 1a).…”

“…Many organic and biological reactions occur through the intermediacy of reactive carbocations, which are hard to detect for their fleeting existence (average lifetime of approximately nanoseconds to picoseconds). − Although persistent carbocations can be prepared in the superacid medium, that does not delineate the role or possible involvement of a carbocation as an intermediate in a typical chemical reaction . The proposals of such unstable intermediate species are often based on kinetics, stereochemical, and product studies without direct evidence …”

“…We noted that the carbocation detection efficiency greatly improved by increasing the spray voltage from 0 to +5 kV, indicating the importance of droplet charge (proton) density and subsequent Coulomb fission process on transferring the carbocation from solution to the gas phase . Thus, ideally, any reaction mixture in the bulk phase that develops a transient carbocation can be impacted with microdroplets for capturing those species to probe their intermediacy. This attempt also laid the foundation of a fairly straightforward MS method to measure the relative change of carbocation abundance in the reaction medium throughout the reaction time. , We also provided mechanistic insight into how water microdroplets outperformed organic microdroplets in the capture of carbocations, demonstrating their survival at the air–water interface over a millisecond (microdroplet lifetime in DESI) with an increase in carbocation lifetime by more than 6 orders of magnitude compared to that in bulk. , The superacidic microdroplet surface with low water density and the high electric field was primarily attributed to carbocation dangling at the air–water interface …”

“…12 We noted that the carbocation detection efficiency greatly improved by increasing the spray voltage from 0 to +5 kV, indicating the importance of droplet charge (proton) density and subsequent Coulomb fission process on transferring the carbocation from solution to the gas phase. 11 Thus, ideally, any reaction mixture in the bulk phase that develops a transient carbocation 3 can be impacted with microdroplets for capturing those species to probe their intermediacy. This attempt also laid the foundation of a fairly straightforward MS method to measure the relative change of carbocation abundance in the reaction medium throughout the reaction time.…”

Carbonylonium ions: the onium ions of the carbonyl group

“…Its researchers have created different terms throughout history looking for a unique, concise and generic name for these kinds of intermediates found when glycosidation reactions take place [6]. “Oxacarbenium ions” [7–11], “oxocarbenium ions” [12–16], “oxycarbenium ions” [17–21], and “carboxonium ions” [22–23] are the most extended terms among the different names found in the literature for these intermediates in this and other fields of Organic Chemistry [24]. All these terms are ambiguous and none describes the actual structure of these intermediates.…”