The interaction of the trans (t) and cis (c) rotamers of the 1-naphthol cation (1-C 10 H 8 O 1 ¼ 1-Np 1 ¼ 1-hydroxynaphthalene 1 ) with nonpolar ligands in the ground electronic state is characterized by IR photodissociation spectra of isolated 1-Np 1 -L n complexes (L ¼ Ar/N 2 ) and density functional calculations at the UB3LYP/6-311G(2df,2pd) level. Size-dependent frequency shifts of the O-H stretch vibration (Dn 1 ) and photofragmentation branching ratios provide information about the stepwise microsolvation of both 1-Np 1 rotamers in a nonpolar hydrophobic environment, including the formation of structural isomers, the competition between H-bonding and p-bonding, the estimation of ligand binding energies, and the acidity of t/c-1-Np 1 . t-1-Np 1 is predicted to be more stable than c-1-Np 1 by 9 kJ mol À1 , with an isomerization barrier of 38 kJ mol À1 . The OH group in t-1-Np 1 is slightly more acidic than in c-1-Np 1 leading to stronger intermolecular H-bonds. Both 1-Np 1 rotamers are considerably less acidic than the phenol cation because of enhanced charge delocalization. The 1-Np 1 ÀAr spectrum displays n 1 bands of the more stable H-bound and the less stable p-bound t-1-Np 1 -Ar isomers. Only the more stable H-bound dimers are identified for t/c-1-Np 1 -L 2 . Analysis of the Dn 1 shifts of the H-bound dimers yields a first experimental estimate for the proton affinity of the t-1-naphthoxy radical (B908 AE 30 kJ mol À1 ). The Dn 1 shifts of 1-Np 1 -L n (n r 2 for Ar, n r 5 for N 2 ) suggest that the preferred microsolvation path begins with the formation of H-bound 1-Np 1 -L, which is further solvated by (nÀ1) p-bound ligands. Ionization of 1-NpÀL n drastically changes the topology of the intermolecular interaction potential and thus the preferred aromatic substrate-nonpolar ligand recognition pattern.

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The sequential microhydration process of protonated imidazole (ImH+) was studied by resonant IR photodissociation spectroscopy of mass‐selected ImH+⋅(H2O)n clusters (see figure). The IR spectra directly probe the effects of both protonation and stepwise hydration on the acidity of the NH groups of ImH+ with relevance to proton transport in biochemical processes and ionic liquids.

The intermolecular interaction between the imidazole cation (Im+ = C3N2H4+) and nonpolar ligands is characterized in the ground electronic state by infrared photodissociation (IRPD) spectroscopy of size-selected Im+-Ln complexes (L = Ar, N2) and quantum chemical calculations performed at the UMP2/6-311G(2df,2pd) and UB3LYP/6-311G(2df,2pd) levels of theory. The complexes are created in an electron impact cluster ion source, which predominantly produces the most stable isomers of a given cluster ion. The analysis of the size-dependent frequency shifts of both the N-H and the C-H stretch vibrations and the photofragmentation branching ratios provides valuable information about the stepwise microsolvation of Im+ in a nonpolar hydrophobic environment, including the formation of structural isomers, the competition between various intermolecular binding motifs (H-bonding and pi-bonding) and their interaction energies, and the acidity of both the CH and NH protons. In line with the calculations, the IRPD spectra show that the most stable Im+-L dimers feature planar H-bound equilibrium structures with nearly linear H-bonds of L to the acidic NH group of Im+. Further solvation occurs at the aromatic ring of Im+ via the formation of intermolecular pi-bonds. Comparison with neutral Im-Ar demonstrates the drastic effect of ionization on the topology of the intermolecular potential, in particular in the preferred aromatic substrate-nonpolar recognition motif, which changes from pi-bonding to H-bonding. .

The authors of this Communication wish to correct a remark in their introductory paragraph: "There have been several unsuccessful attempts to generate and characterize gas-phase H 2 CO 3 by heating solid H 2 CO 3 [3] or NH 4 HCO 3. [12] " This statement is incorrect and misleading, and the authors apologize for their oversight. The sentence should read: "Although there have been several successful attempts to generate and identify gas-phase H 2 CO 3 by heating solid H 2 CO 3 [3] or NH 4 HCO 3 , [12] there is still a lack of detailed experimental information on its structural, spectroscopic, and thermochemical properties."

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The potential energy surface (PES) of C(2)H(5)(+)-N(2) is characterized in detail by infrared photodissociation (IRPD) spectroscopy of mass-selected ions in a quadrupole tandem mass spectrometer and ab initio calculations at the MP2/6-311G(2df,2pd) level. The PES features three nonequivalent minima. Two local minima, 1-N(2)(H) and 1-N(2)(C), are adduct complexes with binding energies of D(0) = 18 and 12 kJ/mol, in which the N(2) ligand is weakly bonded by electrostatic forces to either the acidic proton or the electrophilic carbon atom of the nonclassical C(2)H(5)(+) ion (1), respectively. The global minimum 3 is the ethanediazonium ion, featuring a weak dative bond of D(0) = 38 kJ/mol. This interaction strength is sufficient to switch the C(2)H(5)(+) structure from nonclassical to classical. The 1-N(2)(C) isomer corresponds to the entrance channel complex for addition of N(2) to 1 yielding the product 3. This reaction involves a small barrier of 7 kJ/mol as a result of the rearrangement of the C(2)H(5)(+) ion. The partly rotationally resolved IRPD spectrum of C(2)H(5)(+)-N(2) recorded in the C-H stretch range is dominated by four bands assigned to 3 and one weak transition attributed to 1-N(2)(H). The abundance ratio of 1-N(2)(H) and 3 estimated from the IRPD spectrum as ∼1% is consistent with the calculated free energy difference of 12 kJ/mol. As the ethanediazonium ion escaped previous mass spectrometric detection, the currently accepted value for the ethyl cation affinity of N(2) is revised from -ΔH(0) = 15.5 ± 1.5 to ∼42 kJ/mol. The first experimental identification and characterization of 3 provides a sensitive probe of the electrophilic character and fluxionality of the ethyl cation. Comparison of 3 with related alkanediazonium ions reveals the drastic effect of the size of the alkyl chain on their chemical reactivity, which is relevant in the context of hydrocarbon plasma chemistry of planetary atmospheres and the interstellar medium, as well as alkylation reactions of (bio)organic molecules (e.g., carcinogenesis and mutagenesis of DNA material).

Die Autoren möchten eine Bemerkung in der Einführung dieser Zuschrift korrigieren. Die Aussage "There have been several unsuccessful attempts to generate and characterize gas-phase H 2 CO 3 by heating solid H 2 CO 3 [3] or NH 4 HCO 3 [12] " ist irreführend und muss ersetzt werden durch "Although there have been several successful attempts to generate and identify gas-phase H 2 CO 3 by heating solid H 2 CO 3 [3] or NH 4 HCO 3 , [12] there is still a lack of detailed experimental information on its structural, spectroscopic, and thermochemical properties."