Hydrogen-atom attack on phenol and toluene is ortho-directed

Low-temperature reaction dynamics of paramagnetic species in the gas phase

Radicals are abundant in a range of important gas-phase environments. They are prevalent in the atmosphere, in interstellar space, and in combustion processes. As such, understanding how radicals react is essential for the development of accurate models of the complex chemistry occurring in these gas-phase environments. By controlling the properties of the colliding reactants, we can also gain insights into how radical reactions occur on a fundamental level. Recent years have seen remarkable advances in the breadth of experimental methods successfully applied to the study of reaction dynamics involving paramagnetic species-from improvements to the well-known crossed molecular beams approach to newer techniques involving magnetically guided and decelerated beams. Coupled with ever-improving theoretical methods, quantum features are being observed and interesting insights into reaction dynamics are being uncovered in an increasingly diverse range of systems. In this highlight article, we explore some of the exciting recent developments in the study of chemical dynamics involving paramagnetic species. We focus on low-energy reactive collisions involving neutral radical species, where the reaction parameters are controlled. We conclude by identifying some of the limitations of current methods and exploring possible new directions for the field.

VUV-photolysis of aqueous solutions of hydroxylamine and nitric oxide. Effect of organic matter: phenol

VUV-irradiation of aqueous solutions containing hydroxylamine (NH₂OH) in its acid form (NH₃OH⁺) and phenol (C₆H₅OH) results in the simultaneous mineralization of the organic substrate and the almost quantitative reduction of NH₃OH⁺ to ammonium ions (NH₄⁺). Irradiation of aqueous solutions of NH₃OH⁺ in the absence of organic substrates showed the formation of nitrate (NO₃^-) and nitrite (NO₂^-) and minor quantities of NH₄⁺. In line with these experiments, VUV-irradiation of aqueous solutions of nitrogen monoxide (NO˙) yields NH₄⁺ only when C₆H₅OH is simultaneously mineralized. A possible reaction mechanism is discussed, where reactions of NO˙ and NH₃OH⁺ with hydrogen atoms (H˙), hydroxyl radicals (HO˙) and hydrated electrons (e^-_aq), all generated by the VUV-photochemically initiated homolysis of water, are of great importance to the observed results. In the presence of phenol, competition between phenol and either NO˙ or NH₃OH⁺ for these reactive intermediates in the primary volume of reactions strongly determines the oxidation state and nature of the N-containing products. C-Centered radicals and intermediate products of reactions may also have an important effect on the overall mechanism. The present results are discussed in relation to the actual state of knowledge presented in the literature.

How to computationally calculate thermochemical properties objectively, accurately, and as economically as possible

We have developed the WnX series of quantum chemistry composite protocols for the computation of highly-accurate thermochemical quantities with advanced efficiency and applicability. The W1X-type methods have a general accuracy of ~3–4 kJ mol−1 and they can currently be applied to systems with ~20–30 atoms. Higher-level methods include W2X, W3X and W3X-L, with the most accurate of these being W3X-L. It can be applied to molecules with ~10–20 atoms and is generally accurate to ~1.5 kJ mol−1. The WnX procedures have opened up new possibilities for computational chemists in pursue of accurate thermochemical values in a highly-productive manner.

Hydrogen-adduction to open-shell graphene fragments: spectroscopy, thermochemistry and astrochemistry

We apply a combination of state-of-the-art experimental and quantum-chemical methods to elucidate the electronic and chemical energetics of hydrogen adduction to a model open-shell graphene fragment. The lowest-energy adduct, 1H-phenalene, is determined to have a bond dissociation energy of 258.1 kJ mol-1, while other isomers exhibit reduced or in some cases negative bond dissociation energies, the metastable species being bound by the emergence of a conical intersection along the high-symmetry dissociation coordinate. The gas-phase excitation spectrum of 1H-phenalene and its radical cation are recorded using laser spectroscopy coupled to mass-spectrometry. Several electronically excited states of both species are observed, allowing the determination of the excited-state bond dissociation energy. The ionization energy of 1H-phenalene is determined to be 7.449(17) eV, consistent with high-level W1X-2 calculations.