Oxidopyrylium-Alkene [5 + 2] Cycloaddition Conjugate Addition Cascade (C3) Sequences: Scope, Limitation, and Computational Investigations.

Oxidopyrylium-alkene [5 + 2] cycloaddition conjugate addition cascade (C3) sequences are described. Intramolecular cycloadditions involving terminal alkenes, enals, and enones were investigated. Substrates with tethers of varying lengths delivered five- and six-membered carbocycles and heterocycles thus demonstrating the scope and limitation of the cycloaddition-conjugate addition cascade. Several experiments and theoretical calculations provide evidence for the proposed mechanistic pathway.

Decarboxylation Facilitated by Carbocation Formation and Rearrangement during Steam Distillation of Vetiver Oil.

Density functional theory (DFT) calculations are used to probe the validity of mechanistic proposals for the conversion of isozizanoic acid to 12-norisoziza-5-ene, a reaction that occurs during steam distillation of vetiver oil. While this conversion corresponds overall to a simple decarboxylation, a multistep mechanism involving carbocation intermediates is supported by the computational results.

Mechanistic studies of copper(I)-catalyzed 1,3-halogen migration.

An ongoing challenge in modern catalysis is to identify and understand new modes of reactivity promoted by earth-abundant and inexpensive first-row transition metals. Herein, we report a mechanistic study of an unusual copper(I)-catalyzed 1,3-migration of 2-bromostyrenes that reincorporates the bromine activating group into the final product with concomitant borylation of the aryl halide bond. A combination of experimental and computational studies indicated this reaction does not involve any oxidation state changes at copper; rather, migration occurs through a series of formal sigmatropic shifts. Insight provided from these studies will be used to expand the utility of aryl copper species in synthesis and develop new ligands for enantioselective copper-catalyzed halogenation.

Predicting hydration propensities of biologically relevant α-ketoamides.

Quantum chemical calculations coupled to experiments were used to predict covalent hydration propensities of biologically relevant α-ketoamides. Experimentally determined hydration equilibrium constants for related ketones and aldehydes were compared to computationally determined values to develop a method for predicting hydration equilibrium constants. This method was used on six newly synthesized α-ketoamides to experimentally verify computational predictions. A correlation between calculation and experiment was observed and applied to models of several pertinent APIs. Our results indicate that the keto form is favored for practically all α-ketoamides in biological environs.

Carbocations and the Complex Flavor and Bouquet of Wine: Mechanistic Aspects of Terpene Biosynthesis in Wine Grapes.

Computational chemistry approaches for studying the formation of terpenes/terpenoids in wines are presented, using five particular terpenes/terpenoids (1,8-cineole, α-ylangene, botrydial, rotundone, and the wine lactone), volatile compounds (or their precursors) found in wine and/or wine grapes, as representative examples. Through these examples, we show how modern computational quantum chemistry can be employed as an effective tool for assessing the validity of proposed mechanisms for terpene/terpenoid formation.

Visually impaired researchers get their hands on quantum chemistry: application to a computational study on the isomerization of a sterol.

In molecular sciences, articles tend to revolve around 2D representations of 3D molecules, and sighted scientists often resort to 3D virtual reality software to study these molecules in detail. Blind and visually impaired (BVI) molecular scientists have access to a series of audio devices that can help them read the text in articles and work with computers. Reading articles published in this journal, though, is nearly impossible for them because they need to generate mental 3D images of molecules, but the article-reading software cannot do that for them. We have previously designed AsteriX, a web server that fully automatically decomposes articles, detects 2D plots of low molecular weight molecules, removes meta data and annotations from these plots, and converts them into 3D atomic coordinates. AsteriX-BVI goes one step further and converts the 3D representation into a 3D printable, haptic-enhanced format that includes Braille annotations. These Braille-annotated physical 3D models allow BVI scientists to generate a complete mental model of the molecule. AsteriX-BVI uses Molden to convert the meta data of quantum chemistry experiments into BVI friendly formats so that the entire line of scientific information that sighted people take for granted-from published articles, via printed results of computational chemistry experiments, to 3D models-is now available to BVI scientists too. The possibilities offered by AsteriX-BVI are illustrated by a project on the isomerization of a sterol, executed by the blind co-author of this article (HBW).

Second order Jahn-Teller interactions at unusually high molecular orbital energy separations.

Second order Jahn-Teller (SOJT) effects arise from interactions between filled and empty molecular orbitals of like symmetry. These interactions often lead to structural distortions whose extent is inversely proportional to the energy difference between the interacting orbitals. The main objectives of the work described here are (1) the calculation (using density functional theory methods) of the energies of the valence molecular orbitals in the species EH3 (E = N, P, As or Sb), HEEH (E = C, Si, Ge or Sn), and H2EEH2, (E = C, Si, Ge or Sn) and (2) the correlation of these energies with barriers for planarization or linearization. The calculations suggest an upper limit of about 12 eV energy separation of the interacting levels for SOJT effects to be significant, which is considerably larger than previously thought and implies that SOJT effects may be more common than currently realized.

Quantum chemical study of the isomerization of 24-methylenecycloartanol, a potential marker of olive oil refining.

Quantum chemical calculations on the isomerization of 24-methylenecycloartanol are described. An energetically viable mechanism, with a rate-determining protonation step, is proposed. This rearrangement may find applicability in tests for determining if an olive oil has been refined.