The hydrogen-bonded and van der Waals isomers of phenol⋅⋅nitrogen and phenol⋅⋅carbon monoxide in their neutral electronic (S0) and cation ground state (D0) were studied using ab initio HF/6-31G*, MP2/6-31G*, and B3LYP/6-31G* methods. The hydrogen-bonded isomers have the ligand bound via the hydroxyl group of the phenol ring, while the van der Waals isomers studied have the ligand located above the aromatic ring. For both complexes, the hydrogen-bonded isomer was found to be the most stable form for both the S0 and the D0 states. For phenol⋅⋅carbon monoxide, twice as many isomers as compared to phenol⋅⋅nitrogen were found. The hydrogen-bonded isomer with the carbon end bonded to the hydroxyl group was the most stable structure for both the S0 and the D0 states.

Competition between cation-π interactions and intermolecular hydrogen bonds inalkali metal ion-phenol clusters. II. Phenol trimer Structures and rearrangement reactions of 4 -aminophenol ( H 2 O ) 1 + and 3 -aminophenol ( H 2 O ) 1 + clusters J. Chem. Phys. 123, 074320 (2005); 10.1063/1.2008255 The energetics and structural properties of diazomethyl (HCNN) and cyanomidyl (HNCN) radicals and their related cations and anions from ab initio calculations J. Chem. Phys. 122, 064316 (2005); 10.1063/1.1844314 Intermolecular vibrations of the jet-cooled 2-pyridone2-hydroxypyridine mixed dimer, a model for tautomeric nucleic acid base pairsThe phenol•N 2 complex cation has been studied with a combination of two-color resonant zero kinetic energy ͑ZEKE͒ and mass analyzed threshold ionization ͑MATI͒ spectroscopies to probe the interaction of a polar cation with a quadrupolar solvent molecule. Extended vibrational progressions are observed in three modes which are assigned as the in-plane bend ͑35 cm Ϫ1 ͒, the stretch ͑117 cm Ϫ1 ͒, and in-plane wag ͑130 cm Ϫ1 ͒ intermolecular vibrations, and are consistent with a structure where the N 2 forms a directional bond to the phenol OH group in the plane of the aromatic ring. Ab initio calculations at the UMP2/6-31G*, UHF/cc-pVDZ, and UMP2/cc-pVDZ levels of theory support this assignment. The spectra also provide a value for the adiabatic ionization energy (67 423 cm Ϫ1 Ϯ4.5 cm Ϫ1 ) and an estimate of the dissociation energy of the cluster (1650 Ϯ20 cm Ϫ1 ) which illustrate that the quadrupolar nitrogen molecule binds considerably more strongly to the phenol cation than a rare gas atom. These results constitute the first report of an aromatic•N 2 complex where the interaction can be described in terms of weak hydrogen bonding, rather than in terms of a van der Waals bond to the -system of the benzene ring.

The inversion of 1,4-dioxane has been studied by using ab initio molecular orbital theory at the HF/6-31G* and BLYP/6-31G* levels. A total of 10 stationary points were characterized as energy minima or transition states. Vibrational frequencies were calculated for the chair and two twist-boat conformations. The chair conformation is the lowest in energy, followed by the two twist-boats. The transition state connecting the chair and the twist-boats is a half-chair structure, in which four atoms in the ring are planar. Thermochemical analysis of the chair, twist-boats, and the half-chair structures yields a value of the free energy of activation to ring inversion that is in good agreement with experiment.

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