Structures of Organic Cations in the Gas Phase. Neutral Products from Fluoride Abstraction Examined by NMR

Article abstract of DOI:10.1021/ja00290a007

Structures of 2-fluoroisopropyl cation (1) and 2-propenyl cation (2) in the gas phase have been examined by quenching via ion-molecule reactions and examination of the neutral products by NMR.Both ions are produced by 70-eV electron bombardment of tert-butyl fluoride, and both react with the parent neutral to yield tert-butyl cation.The ion-molecule reaction of 1 yields 2,2-difluoropropane as >90percent of the neutral product.The ion-molecule reaction of 2 yields 2-fluoropropene, as confirmed by preparing 2 from an other source and examining the product from its reaction with tert-butyl-d6 fluoride (3).Allyl fluoride is not detected among the the reaction products.Since this product is observed when allyl bromide is bombarded with 70-eV electrons in the presence of tert-butyl fluoride, its absence in electron bombardment of tert-butyl fluoride alone implies that 2 is the only C3H5⁺ ion produced and that it does not rearrange to the allyl cation under the reaction conditions.The deuterated neutral products from electron impact on 3 alone or in the presence of diethyl ether indicate that 1 does not scramle its hydrogens, even when it contains enough internal energy to expel HF to form 2.The use of deuterium isotope shifts in 19F NMR to study the position and extent of label in neutral products is exemplified as a new tool for probing structures of gaseous cations.