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The electron transmission (ET) and dissociative electron attachment (DEA) spectra of chloroalkyl ethene and ethyne derivatives are reported. B3LYP/6-31G* calculations are employed to evaluate the virtual orbital energies for the optimised geometries of the neutral states of these molecules and other related p-systems. The calculated p* MO energies correlate linearly with the energies of electron attachment to the p* LUMO measured in the ET spectra with a correlation coefficient of 0.993. The vertical attachment energies supplied by B3LYP/6-311+G** calculations, where the basis set includes diffuse functions, are often in significant disagreement with experiment, describing the singly occupied MO of the lowest-lying anion state as a diffuse s* MO rather than a valence p* MO. The relative Cl À anion currents measured in the DEA spectra of the present molecular systems are compared to those previously found in benzene analogues. The Cl À yield reflects the efficiency of intramolecular electron transfer from the p-system (where the extra electron is first trapped) to the remote chlorine atom. Replacement of a carbon atom with a silicon atom in the intermediate saturated alkyl chain causes a notable increase of the Cl À current, ascribed to the lower energy of the empty s* Si-C MOs and consequent greater ability to promote through-bond coupling between the p* and s* C-Cl MOs. Comparison between the corresponding benzene, ethene and ethyne derivatives reveals that the Cl À current is also significantly influenced by the nature of the p-functional group, in agreement with the inverse dependence on energy of the lifetime of the temporary p* anion state.

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The temporary anion states of gas-phase furan, isoxazole, oxazole, pyrrole, pyrazole, imidazole, thiophene, isothiazole, and thiazole are characterized by means of electron transmission spectroscopy. The measured energies of vertical electron attachment are compared with the virtual orbital energies of the neutral state molecules supplied by MP2 and B3LYP calculations with the 6-31G* basis set. The calculated energies, scaled with empirical equations, reproduce satisfactorily the experimental attachment energies. Replacement of a ring CH group with a nitrogen atom increases the electron-acceptor properties, although the stabilization of the π* anion states is not as large as that of the π cation states, in line with the bond length variations caused by aza-substitution. In the spectra of thiophene and isothiazole the first π* resonances display sharp vibrational structure with energy spacing of about 80 meV. The spectrum of isothiazole presents clear evidence for a low-energy (1.61 eV) resonance ascribed to the lowest σ* anion state.

The gas-phase experimental adiabatic electron affinities (AEAs) of the polycyclic aromatic hydrocarbons (PAHs) anthracene, tetracene, pentacene, chrysene, pyrene, benzo[a]pyrene, benzo[e]pyrene, and fluoranthene are well reproduced using the hybrid density functional method B3LYP with the 6-31+G* basis set, indicating that the smallest addition of diffuse functions to the basis set is suitable for a correct description of the stable PAH anion states. The calculated AEAs also give a very good linear correlation with available reduction potentials measured in solution. The AEAs (not experimentally available) of the isomeric benzo[ghi]fluoranthene and cyclopenta[cd]pyrene, commonly found in the environment, are predicted to be 0.817 and 1.108 eV, respectively, confirming the enhancement of the electron-acceptor properties associated with fusion of a peripheral cyclopenta ring. The calculated localization properties of the lowest unoccupied MO of cyclopenta[cd]pyrene, together with its relatively high electron affinity, account for a high reactivity at the ethene double bond of this PAH in reductive processes.

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Supramolecular complexation behavior of cucurbiturils with paramagnetic nitroxide spin probes was examined by (1)H NMR, X-ray diffraction studies of crystals, computation, and EPR. Both cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) form a 1:1 complex with 4-(N,N,N-trimethylammonium)-2,2,6,6-tetramethylpiperidinyl-N-oxy bromide (CAT1). The structure of the complex in the solid state was inferred by X-ray diffraction studies and in the gas phase by computation (B3LYP/6-31G(d)). Whereas ESI-MS data provided evidence for the existence of the complex in solution, indirect evidence was obtained through (1)H NMR studies with a structural diamagnetic analogue, 4-(N,N,N-trimethylammonium)-2,2,6,6-tetramethyl-N-methylpiperidine iodide (DCAT1). The EPR spectrum of the CAT1@CB7 complex consisting of three lines suggested that probe CAT1 is associated with host CB7 such that the nitroxide part is exposed to water. The spectral pattern was independent of the concentration of the complex and the presence of salt such as NaCl. The most interesting observation was made with CB8 as the host. In this case, in addition to the expected three-line spectrum, an additional spectrum consisting of seven lines was recorded. The contribution of the seven-line spectrum to the total spectrum was dependent on the concentration of the complex and added salt (NaCl) to the aqueous solution. The coupling constant for the seven-line spectrum for (14)N-substituted CAT1 is 5 G, and that for the four-line spectrum for (15)N-substituted CAT1 is 7.15 G. The only manner by which we could reproduce the observed spectra by simulation for both (14)N- and (15)N-substituted CAT1@CB8 was by assuming a spin exchange among three nitroxide radicals. To account for this observation, we hypothesize that three CAT1 molecules included within CB8 interact in such a way that there is an association of three supramolecules of CAT1@CB8 (i.e., [CAT1@CB8](3)) in a triangular geometry that leads to spin exchange between the three radical centers. We have established, with the help of 13 additional examples, that this is a general phenomenon. We are in the process of understanding this unusual phenomenon.

The electron transmission spectra of 1,3,5-tri-tert-butylbenzene, 2,4,6-tri-tert-butylpyridine, 2,4,6-tri-tertbutylphosphabenzene, and 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene have been investigated and interpreted by means of quantum chemical calculations. Scaled virtual orbital energies obtained from calculations without employing diffuse functions provide good numerical values for the vertical electron attachment energies (VAEs). B3LYP/6-311+G* VAEs, calculated as the energy difference between the anion and the neutral molecule, were in good agreement with experiment, with the molecules investigated here having VAEs of less than about 1 eV. The first anion state of phosphabenzene is predicted to lie at the edge of stability. The gradual replacement of CH units by phosphorus in π systems results in a significant stabilization of the anionic states, which contrasts with the relative invariance of the electron donor properties. This behavior can be explained by considering that for the PdC π system both the interaction between the atomic levels ( ) and the overlap are smaller than for the CdC π system.