Photochemistry of Benzylallene: Ring-Closing Reactions to Form Naphthalene

Conformer Selection by Matter-Wave Interference

We establish that matter-wave diffraction at near-resonant ultraviolet optical gratings can be used to spatially separate individual conformers of complex molecules. Our calculations show that the conformational purity of the prepared beam can be close to 100% and that all molecules remain in their electronic ground state. The proposed technique is independent of the dipole moment and the spin of the molecule and thus paves the way for structure-sensitive experiments with hydrocarbons and biomolecules, such as neurotransmitters and hormones, which have evaded conformer-pure isolation so far.

CuO/I2-mediated intramolecular annulation for the synthesis of 2-aroyl-3-hydroxy-4-iodonaphthalenes

A novel method for the direct synthesis of 2-aroyl-3-hydroxy-4-iodonaphthalenes has been developed via CuO/I₂-mediated domino reactions.

Jet-cooled spectroscopy of the α-methylbenzyl radical: probing the state-dependent effects of methyl rocking against a radical site

The state-dependent spectroscopy of α-methylbenzyl radical (α-MeBz) has been studied under jet-cooled conditions. Two-color resonant two-photon ionization (2C-R2PI), laser-induced fluorescence, and dispersed fluorescence spectra were obtained for the D0-D1 electronic transition of this prototypical resonance-stabilized radical in which the methyl group is immediately adjacent to the primary radical site. Extensive Franck-Condon activity in hindered rotor levels was observed in the excitation spectrum, reflecting a reorientation of the methyl group upon electronic excitation. Dispersed fluorescence spectra from the set of internal rotor levels are combined with the excitation spectrum to obtain a global fit of the barrier heights and angular change of the methyl group in both D0 and D1 states. The best-fit methyl rotor potential in the ground electronic state (D0) is a flat-topped 3-fold potential (V3" = 151 cm(-1), V6" = 34 cm(-1)) while the D1 state has a lower barrier (V3' = 72 cm(-1), V6' = 15 cm(-1)) with Δφ = ± π/3, π, consistent with a reorientation of the methyl group upon electronic excitation. The ground state results are compared with calculations carried out at the DFT B3LYP level of theory using the 6-311+G(d,p) basis set, and a variety of excited state calculations are carried out to compare against experiment. The preferred geometry of the methyl rotor in the ground state is anti, which switches to syn in the D1 state and in the cation. The calculations uncover a subtle combination of effects that contribute to the shift in orientation and change in barrier in the excited state relative to ground state. Steric interaction favors the anti conformation, while hyperconjugation is greater in the syn orientation. The presence of a second excited state close by D1 is postulated to influence the methyl rotor properties. A resonant ion-dip infrared (RIDIR) spectrum in the alkyl and aromatic CH stretch regions was also recorded, probing in a complementary way the state-dependent conformation of α-MeBz. Using a scheme in which infrared depletion occurs between excitation and ionization steps of the 2C-R2PI process, analogous infrared spectra in D1 were also obtained, probing the response of the CH stretch fundamentals to electronic excitation. A reduced-dimension Wilson G-matrix model was implemented to simulate and interpret the observed infrared results. Finally, photoionization efficiency scans were carried out to determine the adiabatic ionization threshold of α-MeBz (IP = 6.835 ± 0.002 eV) and provide thresholds for ionization out of specific internal rotor levels, which report on the methyl rotor barrier in the cation state.

Removal of sulfur compounds from diesel using ArF laser and oxygen

A laser-based technique for deep desulfurization of diesel and other hydrocarbon fuels by removal of dimethyldibenzothiophene (DMDBT), a persistent sulfur contaminant in fuel oils has been developed. We report a selective laser excitation of DMDBT in diesel and model compounds such as n-hexane in a reaction chamber under oxygen environment where oxidative reactions can take place. ArF laser emitting at 193 nm was employed for excitation of oxygen and DMDBT, while for process optimization, the laser energy was varied from 50 to 200 mJ/cm(2). The laser-irradiated DMDBT solution under continuous oxygen flow was analyzed by UV absorption spectrometer to determine the photochemical oxidative degradation of DMDBT. In just 5 min of laser irradiation time, almost 95% DMDBT was depleted in a diesel containing 200 ppm of DMDBT. This article provides a new method for the removal of sulfur compounds from diesel by laser based photochemical process.