1- and 2-Adamantyl Radicals and Cations in the Gas Phase:  Thermochemistry and Mass Spectrometry

Abstract

The heats of formation of the 1-and 2-adamantyl cations and of the 1-adamantyl radical have been measured directly by electron impact appearance energies. The values are. The results also lead to a value of 16 kcal mol -1 for the heat of formation of the 2-adamantyl radical. Collision-induced dissociation mass spectra of the 1-and 2-adamantyl cations allow low internal energy ions to be distinguished. However, it is shown that at higher internal energies the two ions share a common potential energy surface. This is supported by the statistical mixing of all hydrogen and deuterium atoms, prior to the lowest energy dissociation channel, in the 1-adamantyl-3d 1 + isotopomer.

Trapping of a tert-adamantyl peroxyl radical in the gas phase

“…1,4,5 As such, the unusual structure and reactivity of bridgehead radicals presents an extremely attractive target for investigation in the isolation in the gas phase. While the gas phase thermochemistry and spectroscopy of the 1-adamantyl radical have been probed by indirect methods 6,7 and its structure has been predicted by calculation, 8 no reliable procedure for the preparation, isolation and reaction of this intermediate has previously been described. In the present study we have prepared a gas phase radical anion which includes a bridgehead adamantyl radical and a carboxylate anion moiety isolated from each other by the rigid adamantane cage.…”

The Standard Enthalpy of Formation of the 1-Adamantyl Cation in the Gas Phase. An Experimental and ab Initio Re-assessment

“…Holmes and co-workers have recently used appearance energies to determine the standard enthalpy of formation of 1-adamantyl cation ( 1 + ) in the gas phase, Δ f H ° m ( 1 + ,g). The value they reported, 152 ± 3 kcal mol -1 , significantly differs from the values obtained by other methods (in the range 158−164 kcal mol -1 ) .…”

“…Holmes and co-workers have recently used appearance energies to determine the standard enthalpy of formation of 1-adamantyl cation ( 1 + ) in the gas phase, Δ f H ° m ( 1 + ,g). The value they reported, 152 ± 3 kcal mol -1 , significantly differs from the values obtained by other methods (in the range 158−164 kcal mol -1 ) . Inasmuch as carbocations are important chemical species, , this discrepancy has prompted us to reexamine the problem by means of experimental and computational techniques.…”

Synthesis of Higher Diamondoids and Implications for Their Formation in Petroleum

“…Moreover, the relative stabilities of carbocations and alkyl radicals are quite different, especially when polycyclic structures are taken into account. For instance, while the secondary and tertiary diamondoid CH bonds have practically the same bond dissociation energies,28 the heterolytic cleavages of these bonds differ significantly in energy 29. As the isomer distribution in the extracts from raw oil does not reflect the thermodynamic stability of the diamondoids or their cations,7, 18 a different formation mechanism must be considered.…”