The first example of direct structural characterization of polyaromatic ions by coupling a Fourier transform ion cyclotron resonance mass spectrometer with an infrared free-electron laser is presented. Measurement of the IR spectra of selectively prepared ionic reactive intermediates is allowed by the association of the high peak power and wide tunability of the laser with the flexibility of the spectrometer, where several mass selection and ion reaction steps can be combined, as demonstrated in the case of iron cation complexes of hydrocarbons. The present experimental setup opens the way to understanding chemical reaction paths.

The dissociation dynamics of n-butylbenzene ions have been measured as a function of the parent ion internal energy. Ions were produced by dispersed synchrotron radiation and energy selected by photoelectron photoion coincidence. The branching ratio of the two fragment ions of mass 91 and 92 was measured over an ion internal energy range from 2 to 6.5 eV. This ratio, which varies from 0.05 to 8.0 is a useful thermometer for the n-butylbenzene ion internal energy. The measured dissociation rates for the production of C7H8+ were modeled with RRKM/QET calculations, from which an activation energy of 0.99 eV was derived. The assumption of a tight transition state with AS = -7 cal/K is necessary in order to account for the slow rise in the dissociation rate with ion internal energy. The small kinetic energy released in the dissociation indicates that the rate-determining step is an isomerization reaction, prior to the actual dissociation.

CpCo(CO)2 has been found to catalyze the cocyclization of o-diethynylbenzenes with alkynes to give 2,3-disubstituted biphenylenes. This method has been applied to the total synthesis of [3]phenylene (3) and some silylated derivatives 4 and 5. The spectral, chemical, and structural data indicate this system to be a highly unusual "benzocyclobutadienoid" hydrocarbon framework containing [4n + 2] tt electrons. The central benzene ring is highly reactive to hydrogenation, alkyllithium addition, and transition-metal complexation. Reduction and oxidation furnishes the corresponding An dianions and dications. The nuclear magnetic resonance data of these ions show unexpected trends in comparison with the neutral parent system.