The factors controlling chemo-, regio-, and stereoselectivity in a cascade of reactions starting from a bis(cyanoalkenyl)oxime and proceeding via nitrone cycloadditions, have been unravelled through a series of density functional calculations with several different functionals. Both kinetic and thermodynamic control of the reaction cascade are important depending upon conditions. Kinetic control is analysed by the distortion/interaction model and is found to be dictated by differences in distortions of the cycloaddends in the transition states. A new mechanism competing with that originally proposed in the application of these reactions to the histrionicotoxin synthesis is discovered in these studies.

In this study, the origins of diastereoselectivity in the hydrogen bonding assisted Diels-Alder reactions of chiral dienes with achiral dienophiles have been investigated with density functional methods. The distortion/interaction model has been applied to shed light on the origins of selectivity. C9-Substituted chiral anthracene templates (R = (CH(3))(OCH(3))(H), R = (CH(3))(OH)(H), R = (CH(3))(CH(2)CH(3))(H) and R = (-CH(2)-C(CH(3))(OCH(3))(H)) are used to rationalize the role of a stereogenic center and H-bonding on the product distribution ratio. Even though hydrogen bonding increases the reactivity of the diene, the stereoselectivity is reduced because of the hydrogen bonding capacity of both diastereomeric transition states. The interaction energies of the studied anthracene templates with N-methyl maleimide at the transition state correlate linearly with an increase in reactivity. The selectivity is determined by both favorable distortion and interaction energies. The π-facial selectivity induced by the presence of a chiral auxiliary in 1-substituted 1,3-pentadienes (R1 = (CH(3))(OCH(3))(H) and R1 = (CH(3))(OH)(H)) has also been modeled in order to rationalize the role of the stereogenic center and H-bonding on the stereoselectivity of an aliphatic diene. In both parts, the product distribution ratios calculated from Boltzmann distributions based on Gibbs free energies are in reasonable agreement with the experimental results. Finally the role of OH-substituted five-membered pyrrolidine on C9 of anthracene is investigated since the successful usage of the conformationally rigid pyrrolidines in asymmetric synthesis is well known. Overall, both in the acyclic system and in anthracene, the facilitation due to H-bonding is reflected in the interaction energies: the higher the difference in interaction energies in the transition structures of the two diastereomers, the more selective the H-bonding assisted Diels-Alder reaction is.

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The study covers a thorough assessment of the overall degradation of diclofenac-Na (DCF) by high-frequency ultrasound, focusing particularly on identification, interpretation, and characterization of the oxidation byproducts and their reaction mechanisms. It was found that sonication of 5 mg L(-1) DCF at near neutral pH rendered complete conversion of the compound, 45 % carbon, 30 % chlorine, and 25 % nitrogen mineralization. Density functional theory (DFT) calculations confirmed the experimentally detected major byproduct 2,6-dichloroaniline, the formation of which was explained by OH• addition to the ipso-position of the amino group. The stability of UV absorption at around 276-280 nm throughout reaction was in agreement with the detected byproduct structures, i.e., the presence of amino/amine groups and phenolic, aniline, benzene, and quinine-type derivatives, which all absorbed at around the same band. Microtox toxicity of the reactor aliquots at early reaction showed that initially the reaction products, specifically 1-(2,6-dichlorophenyl)-2-indoline-one, were very toxic; subsequently toxicity exhibited a fluctuating pattern, and a steady declination towards the "non-toxic" level was observed only after 90 min. Oxygen uptake analysis also revealed the formation of harmful products at early reaction, but the reactor was totally biodegradable upon 1-h sonication.