Gas-phase analogs of cage effects

Abstract

When a molecule dissociates, three types of transport phenomena compete with recombination of the fragments. Translational diffusion carries the cleavage products into the bulk medium, diluting them so that reencounters steadily become less probable with time. Heat conduction equilibrates the energies of the products with that of the medium, dissipating any excess energy left over from surmounting an activation barrier. Finally, rotational diffusion washes out the angular correlations dictated by the transition state. At the instant a bond is broken the fragments point toward one another in a way that is most conducive to re-forming the bond. The memory of this nascent relative orientation is soon lost as the fragments start to rotate independently of each other. This is portrayed schematically in eq 1. D a d McAdoo grew up in westem Pennsylvania, recelved his bachelor's degree from Lafayette Corkge and hls Ph.D. from Comell Unlverslty (wlth F. W. McLafferty), and dld po&doctml work at Johns Hopklns Unlverslty. He has been employed by the USDA, U n h Carblde, and Jet Ropulsbn Laboratory, and he ls currently a " b r of the Marine Bbmdical Institute and professor of human bkbglcal chemistry and genetics, cellular physiobgy and membrane bkphydcs, and nwocrcknces at the University of Texas Medlcal Branch at Qahton. Other sdentlflc Interests are neurochemistry and neurophyslology. Nonprofeaslonal Intere8ta Include the exploratbn of caves. Tom Morton waa bom In Loo Angebs, where his forebears (both Hellman and Morton) were employed by the motion pichrre Industry. He recelved h18 AB from Haward In 1968 In clas.sks (&e&) and flne arts and his Ph.D. from Cattech under the joht dbctbn of R. Q. Bergman and J. L. Beauchamp. Since 0 1993 American Chemical Society (14) (a) Audier, H. E.; Milliet, A.; Leblanc, D.; Morton, T. H. J. Am. Chem. SOC. 1992,114,2020-2027. (b) Cao, J. R.; George, M.; Holmes, J. L.; Siroie, M.; Terlouw, J. K.;Burgers, P. C. J. Am. Chem. SOC. 1992,114, (15) Postma, R.; Ruttink, P. J. A.; van Baar, B. L. M.; Terlouw, J. K.; Holmes, J. L.; Burgers, P. Chem.

A photoionization study of the ion-neutral complexes CH3CH +CH3·CH2CH3] and CH3CH2CH+CH3·CH3 in the gas phase: Formation, H-transfer and C—C bond formation between partners, and channeling of energy into dissociation

“…I on-neutral complexes (ionic and neutral fragments held together primarily by noncovalent attractions) are often intermediates in low energy dissociations of ions in the gas phase [1][2][3][4][5]. As the energy in an ion is increased toward the threshold for simple dissociation, partial dissociation to noncovalently bound fragments that can react with each other begins to occur [6][7][8].…”

Gas‐Phase Nucleophilic Aromatic Substitution between Piperazine and Halobenzyl Cations: Reactivity of the Methylene Arenium Form of Benzyl Cations

“…All compounds were purified after synthesis. The structures were confirmed by 1 H and 13 C NMR spectroscopy and mass spectrometry.…”

“…[11] In the present study, the reactants of piperazine and halobenzyl cations were simultaneously in-situ-generated by collision-induced dissociation (CID) of protonated N-(halobenzyl)piperazines using an ESI ion trap mass spectrometer (Scheme 2). [12] The two nascent reactants with a suitable amount of internal energy are consequently trapped in an ion/neutral complex [13] through electrostatic interactions. The two components of the ion/neutral complex are able to rotate with respect to one another, and therefore they show reactivities similar to those expected for the isolated species.…”

Fragmentation of Protonated N-(3-Aminophenyl)Benzamide and Its Derivatives in Gas Phase

“…Ion-neutral complexes (INC) have been recognized as an important type of reactive intermediates, and many times formations of INC are critical steps of fragmentation pathways of ionized species [24,25]. Evidence of INC have been frequently found in many ion fragmentation reactions with CID experiments [26][27][28][29][30][31][32].…”