This review will be concerned with the gas phase chemistry of 1,2- and 1,3-
dipolar systems that contain a carbon-nitrogen bond. Although most of these
compounds are stable molecules under normal conditions, certain congeners
are reactive species that cannot be prepared using conventional procedures.
The isolation and observation of these elusive compounds therefore require
appropriate experimental conditions such as those provided by the gas phas
e of a mass spectrometer: In these experiments, the radical cations, corres
ponding to the molecule under study, must be prepared via indirect procedur
es, including dissociative electron ionization, on-line flash-vacuum pyroly
sis-mass spectrometry, or ion-molecule reactions. Their characterization is
mainly based on collisional activation and ion-molecule reactions. The for
mation of the corresponding highly reactive neutrals is attempted by neutra
lization-reionization mass spectrometry. This review presents more than one
hundred different molecules together with their methods of preparation and
the experiment used to identify them. (C) 2000 John Wiley & Sons, Inc.