2534-77-2Relevant articles and documents
Aqueous Microdroplets Capture Elusive Carbocations
Kumar, Anubhav,Mondal, Supratim,Banerjee, Shibdas
supporting information, p. 2459 - 2463 (2021/02/16)
Carbocations are short-lived reactive intermediates in many organic and biological reactions that are difficult to observe. This field sprung to life with the discovery by Olah that a superacidic solution allowed the successful capture and nuclear magnetic resonance characterization of transient carbocations. We report here that water microdroplets can directly capture the fleeting carbocation from a reaction aliquot followed by its desorption to the gas phase for mass spectrometric detection. This was accomplished by employing desorption electrospray ionization mass spectrometry to detect a variety of short-lived carbocations (average lifetime ranges from nanoseconds to picoseconds) obtained from different reactions (e.g., elimination, substitution, and oxidation). Solvent-dependent studies revealed that aqueous microdroplets outperform organic microdroplets in the capture of carbocations. We provide a mechanistic insight demonstrating the survival of the reactive carbocation in a positively charged aqueous microdroplet and its subsequent ejection to the gas phase for mass spectrometric analysis.
The halogenolysis of organoboranes
Morrill,Lu,Brister,O'Shaughnessy,Belfield
, p. 973 - 976 (2007/10/02)
Transmercuration of tri-exo-2-norbornylborane followed by chlorinolysis of the resultant organoborane is a low yield (≤5%) method of producing exo-2-norbornyl chloride. The primary source of this low yield is the inefficient transmercuration of the sterically restricted organoborane. Yields of alkyl halide are substantially higher (up to 63%) when the organoborane undergoes direct chlorinolysis promoted by boron trichloride. Even higher yields (approaching 80%) are obtained when brominolysis of the organoborane is carried out. Controls suggest that at least part of the reason for the higher yield with bromine is due to the greater stability of the product under the reaction conditions. Despite the general retention aspects (exo-borane gives largely exo-halide) of these halogenolyses, deuterium labeling studies show that these reactions are accompanied by substantial Wagner-Meerwein rearrangement, very possibly due to boron trihalide induced rearrangement of the norbornyl halide product.
Photochemistry of alkyl halides. 12. Bromides vs Iodides
Kopp, Paul J.,Adkins, Rick L.
, p. 2709 - 2717 (2007/10/02)
Conditions have been developed for optimizing ionic photobehavior material balances from alkyl bromides. Hydroxide ion as an efficient for the byproduct HBr while giving minimal competing photoreduction via electron transfer to the alkyl bomide. The photobehavior of bromides 1, 11, 25, and 40 has examined and with that of the corresponding iodides 2, 12, 26, 41 under conditions. In each case, the bromide higher yields of products derived from out of cage radical intermidiates than the corresponding iodide. However, with the 2-norbornyl bromides 11 and iodides 12 showed that, of products not formed from the out of cage 2-norbornyl radical 13, the bromides 11 gave a higher percentage of products from the ionic intermediates 15 and 16 than did the iodides. Thus, electron transfer within the radical pair 14 is apparently more rapid for bromides than iodides, as expected on the of the relative electronegativities of bromine iodine. It is that the substantially higher yields of out of radical products from alkyl bromides may be due in to formation of the radical pair with greater excess energy, which results in more rapid escape from the cage. The epimeric 2-norbornyl bromides 11x and 11n underwent no detectable interconversion and afforded somewhat different product ratios. The more hindered epimer 11n underwent conversion to products at a slower than 11x. By contrast, 12x and 12n underwent substantial interconversion via out of transfer of an iodine atom from iodide 12 to radical 13. Epimerization was significantly attenuated in the more viscous solvent tert-butyl alcohol.
