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Abstract: The photoisomerization equilibrium between the model tannins (-)-catechin and (-)-epicatechin in aqueous solution was investigated at the density functional level of theory to gain insights into the action of [...]

Vertical and adiabatic ionization energies (IEs) and electron affinities (EAs) were calculated for the n = 1-10 [n]acenes using a wide range of semiempirical, Hartree-Fock, density functional, and second-order Moller-Plesset perturbation theory model chemistries. None of the model chemistries examined was able to accurately predict the IEs or EAs for both short- through long-chain [n]acenes, as well as for extrapolations to the polymeric limit, when compared to available experimental and benchmark theoretical data. Except for 6-31G(d), the choice of the basis set does not affect B3LYP results significantly. Analogous calculations using a suite of eight modern and (or) popular density functionals for the n = 1-10 [n]phenacenes revealed similar problems in estimating the IEs and EAs of these compounds, with the sole exception of the M062X functional for adiabatic IEs and potentially the APFD, B3LYP, and MN12SX functionals for adiabatic EAs. The poor IE/EA prediction performance for the parent [n]acenes and [n]phenacenes may extend to their substituted derivatives and heteroatom-substituted analogs. Consequently, caution should be exercised in the application of non-high-level calculations for estimating the IE/EA of these important classes of materials. Key words: [n]acenes, [n]phenacenes, ionization energies, electron affinities, benchmarking, organic electronics. Nous avons calcule les energies d'ionisation (EI) et les affinites (AE) electroniques verticales et adiabatiques des [n]acenes ou n = 1-10 a l'aide d'un large eventail de modeles chimiques semi-empiriques, de la methode de Hartree-Fock, de la theorie de la fonctionnelle de la densite et de la theorie de la perturbation de deuxieme ordre de Moller-Plesset. Aucun des modeles chimiques evalues n'a ete en mesure de predire avec exactitude les EI ni les AE pour toutes les valeurs de n des [n]acenes, ni les extrapolations a la limite polymerique, lorsque les resultats ont ete compares aux valeurs experimentales publiees et aux donnees theoriques de reference. A l'exception de la base 6-31G(d), le choix de la base n'a eu que peu d'incidence sur les resultats de la fonctionnelle B3LYP. En appliquant des calculs analogues a l'aide d'une suite de huit fonctionnelles de la densite modernes et/ou communes aux [n]phenacenes ou n = 1-10, nous avons observe des problemes similaires quant a l'estimation des EI et des AE de ces composes, a l'exception d'un seul cas, celui de la fonctionnelle M062X appliquee au calcul des EI adiabatiques, et peut-etre ceux des fonctionnelles APFD, B3LYP et MN12SX appliquees au calcul des AE adiabatiques. La pietre capacite de prediction des EI et des AE des [n]acenes et des [n]phenacenes non substitues pourrait s'etendre a leurs derives substitues et aux analogues heteroatomiques substitues correspondants. Par consequent, il convient d'aborder avec prudence l'application de calculs de niveau non eleve a l'estimation des EI et des AE de ces importantes classes de composes. [Traduit par la Redactionj. Mots-cles: [n]acenes, [n]phenacenes, energies d'ionisation, affinites electroniques, referenciation, electronique organique., Introduction The [n]acenes and their derivatives offer potential in the field of organic electronics. (1-3) Consequently, the molecular properties of these compounds are of interest in terms of both experimental [...]

Studies on student learning during primary- and secondary-school course-related field trip activities have shown lasting cognitive and socio-cultural effects. However, fewer studies have investigated the potential benefits of incorporating field trip activities into post-secondary education. The curriculum in a first-year university chemistry course provides the foundations for understanding processes we encounter every day. Thus, field trips can provide an opportunity to help students see beyond their everyday experiences into the world around us through a chemist's eyes. As a way of seeing their lecture material in action, taking students on field trips to water treatment plants helps describe a real-world application of solution stoichiometry and polymer chemistry. Similarly, a trip to a winery assists understanding of chemical transformations that occur in organic molecules, and a trip to wastewater treatment plants enables students to see applications of acid-base and redox chemistry. These experiences allow students to engage the material on a level difficult to convey or appreciate in the classroom. Field trips can also satisfy instructor motivations to not only facilitate learning as a way of connecting with the curriculum, but also to engage students by (a) providing new learning experiences, (b) fostering interest and motivation in students, (c) promoting lifelong learning, and (d) engaging with the local science and technology communities. (Contains 1 figure and 3 textboxes.)

In our focus on material that must be covered in a content-rich course such as first-year chemistry, we often neglect the development of other essential skills such as reading, writing, and critical thinking. The primary research literature summary assignment described attempts to address this issue. The purpose of the assignment is to introduce first-year students to the primary scientific literature, including the ability to search and access hard-copy and electronic library resources. In addition, the assignment engages students towards more broadly contextualizing chemical theory covered during lectures. In our experience, we found the curriculum addition is neither a time burden to students in its preparation, nor to instructors in its assessment. These factors allow the exercise to be implemented in courses of any size. (Contains 1 table and 1 figure.)

The photochemistry of 3- and 4-acetylphenylacetic acids (6 and 7) has been studied in aqueous solution. This work is a continuation of research efforts aimed at understanding the structural effects on the efficacy for benzyl carbanion photogeneration via photodecarboxylation. The nitro group (at the 3- and 4-positions) is known to be an exceptionally good activating group on the benzene ring--because of its enhanced electron-withdrawing effect in the excited triplet state--for photodecarboxylation and the related photo-retro-aldol type process. It is shown in this work that the acetyl group is an equally good activating group for the photodecarboxylation. Thus, the photochemistry of 6 and 7 parallels much of what was observed for the corresponding nitrophenylacetic acids 1 and 2. Both 6 and 7 photodecarboxylate efficiently ([[PHI].sub.d] = 0.60 and 0.22, respectively, at pH 7) via the carboxylate form, to give observable (by laser flash photolysis) benzyl carbanion or related intermediates. The meta isomer 6 displays an acid-catalyzed pathway for photodecarboxylation at pH < 3 and along with its enhanced overall reactivity, is consistent with a meta effect of the acetyl group. Triplet state reactivity is inferred from sensitization and laser flash photolysis experiments. Based on the results of this work, the acetyl group may now be viewed as an "enhanced" electron-withdrawing group (in the excited state) when attached to a benzene ring (i.e., in acetophenone derivatives) that is capable of inducing ionic reactions, which is not the traditional photochemistry that is expected from such compounds. Key words: photodecarboxylation, acid catalysis, acetophenone, photogenerated carbanion, enol, enolate.