Half a century of scrambling in organic ions: Complete, incomplete, progressive and composite atom interchange

摘要: Positional exchange of atoms within the given frameworks gaseous ions and positional framework themselves-generally addressed as atom scrambling-belong to best-known but, in same time, most irritating characterics reactions organic gas phase. Half a century now after phenomenon scrambling has been uncovered, this article spans arbitrarily number examples from manifold mass spectrometry. Starting out best-established systems (C7H8.+-->C7H7+ + H-.), illustrate an ubiquitous but very complex case, various that undergo complete ("statistical") hydrogen are presented. This includes two chemically different cases where 21 protons completely interchanged lifetime ions. Some tutorial aspects woven here on simple combinatorics which have be applied for calculating "statistical pattern" is expected relative abundances isotopomeric fragment (and neutral fragments) formed upon fragmentation ion undergone equilibration set over molecular sites. Besides species undergoing scrambling, some incompletely ones also discussed, including case random distribution reached separately moities alongside with slow process between these moieties. Ionic incomplete progressive (i.e. lifetime-dependent) way full ("randomization") partners discussed. Finally, returning apparently even- odd-electron carbocations, several "fractional" behavior demonstrated. Here, or more fractions reacting exhibit distinct behavior, example, one them fragmenting specifically, another exchange, still equilibration, all contributing "composite" pattern spectrum. Although selection presented reflects part die author's personal fascination years, it hoped studies variety, beauty complexity phenomena will remain alive at least fun when studied getting larger larger. (Int J Mass Spectrom 213 (2002) 101-144) (C) 2002 Elsevier Science B.V.