Strong hydrogen bonding in the gas phase: fluoromethane⋯hydronium versus fluoromethane⋯ammonium

Photoionization of 2,3-dimethyl-2-butanol (thexyl alcohol): interaction between the charged and expelled fragments

Photoionization studies of (CH(3))(2)CHC(CH(3))(2)OH (tert-hexyl alcohol, also called thexyl alcohol) exhibit four fragmentations below 10 eV. As with other tertiary alcohols, no molecular ion is detected. The only ion observed at threshold corresponds to propane loss. Examination of a deuterated analogue, (CH(3))(2)CHC(CD(3))(2)OH, shows only loss of C(3)H(7)D, implying that the fragment ion has the structure of ionized acetone enol. There is no evidence for reversible deuterium transposition, as has been reported for isotopomers of the homologous secondary alcohol (CH(3))(2)CHCH(CH(3))OH. Propane loss from thexyl alcohol is attributed to intermediacy of ion-neutral complexes containing isopropyl radical and O-protonated acetone. Simple cleavage to give O-protonated acetone has an appearance energy 18 kJ mol(-1) higher than that of propane loss. Thermochemical estimates and ab initio calculations both predict that methyl loss should have a lower threshold than the fragmentation leading to isopropyl loss, but experiments show the appearance energy to be 6 kJ mol(-1) higher. This is consistent with previous reports of reverse activation barriers for methyl cleavages. Finally, formation of tert-hexyl cation, (CH(3))(2)CHC(CH(3))(2)(+), is observed with an appearance energy comparable to that of methyl loss, substantially below that predicted for OH radical expulsion from the molecular ion. The comparatively low threshold of this fragmentation is ascribed to ion-pair formation (concomitant with hydroxide ion) directly from an electronically excited neutral. Interactions between charged and neutral fragments (including energetics, bond orders <1, and electrical charges on molecular fragments) are explored using a combination of DFT and ab initio methods, along with topological analysis using the Atoms in Molecules approach.

The ferrocene--lithium cation complex in the gas phase

The stable isomers of the ferrocene--lithium cation gas-phase ion complex have been studied with the hybrid density functional theory. The method of calculation chosen has been tested checking its performance for the more studied protonated ferrocene species. Our calculations demonstrate that the procedure used is reliable. We have found two isomers of the ferrocene--lithium cation complex separated by a barrier of 25.6 kcal/mol. The most stable isomer of this complex has Li(+) on-top of one of the cyclopentadienyls, while in the least stable isomer Li(+) binds the central iron metal. The latter isomer has been characterized as a planetary system in the sense that Li(+) has one thermally accessible planar orbit around the central ferrocene moiety. Our calculations lead to a value of ferrocene's gas-phase lithium cation basicity of 37.4 kcal/mol for the on-top complex and 29.4 kcal/mol for the metal-bound complex.