Atomic pseudopotentials for reproducing π-orbital electron behavior in sp 2 carbon atoms

International audienceA pseudo-potential system for an sp 2 carbon atom is built and tested as a building block for various pseudo-hydrocarbon polyenes and polycyclic aromatic hydrocarbons. This pseudo-system has a central charge of Z = 1, it contains only one electron. It is employed in ab-initio calculations in which several physical characteristics including the orbital energies and first ionisation energy, as well as first excitation energy and UV spectra, are found to be well-reproduced by the pseudo-system. Remarkably, not only are the π excitation energies in good agreement with the reference calculations, but also transition densities and intensities, confirming that the virtual space obtained with the pseudo-potentials is of excellent quality. Finally, this approach is capable of reproducing the π electron systems of small or large, planar or near-planar hydrocarbons at low computational cost

Monsters: interdisciplinary explorations in monstrosity

There is a continued fascination with all things monster. This is partly due to the popular reception of Mary Shelley’s Monster, termed a “new species” by its overreaching but admiringly determined maker Victor Frankenstein in the eponymous novel first published in 1818. The enduring impact of Shelley’s novel, which spans a plethora of subjects and genres in imagery and themes, raises questions of origin and identity, death, birth and family relationships as well as the contradictory qualities of the monster. Monsters serve as metaphors for anxieties of aberration and innovation. Stephen Asma (2009) notes that monsters represent evil or moral transgression and each epoch, to speak with Michel Foucault, evidences a “particular type of monster” (2003, 66). Academic debates tend to explore how social and cultural threats come to be embodied in the figure of a monster and their actions literalize our deepest fears. Monsters in contemporary culture, however, have become are more humane than ever before. Monsters are strong, resilient, creative and sly creatures. Through their playful and invigorating energy they can be seen to disrupt and unsettle. They still cater to the appetite for horror, but they also encourage us to feel empathy. The encounter with a monster can enable us to stop, wonder and change our attitudes towards technology and our body and each other. This commentary article considers the use of the concepts of ‘monsters’ or ‘monstrosity’ in literature, contemporary research, culture and teaching contexts at the intersection of the Humanities and the Social Sciences

Pseudopotentials for the study of molecular properties

Les pseudopotentiels permettent de simplifier les calculs moléculaires en remplaçant des atomes ou des groupements chimiques par des pseudosystèmes simples associés à des fonctions mathématiques rapides à évaluer. Dans ce travail, de nouveaux pseudopotentiels ont été créés pour la reproduction des propriétés électroniques de fragments carbonés. Initialement j’ai travaillé sur des systèmes contenant des carbones hybridés sp2 et j’ai pu reproduire plusieurs propriétés de base (énergie de la HOMO, énergie de 1ère ionisation, énergie d’excitation) de ces systèmes (polyènes et hydrocarbures polycycliques aromatiques) avec une précision satisfaisante. La procédure d’optimisation des paramètres des pseudopotentiels a été généralisée grâce à l’écriture d’un programme en Python, qui m’a permis d’obtenir des pseudopotentiels pour d’autres types de fragments carbonés : un pseudo sp3 à 1 électron, un pseudo sp3 à 2 électrons et un pseudo sp2 supplémentaire à 2 électrons. J’ai aussi réoptimisé les potentiels originaux (sp2 à 1 électron) spécifiquement pour le calcul des spectres UV et ECD. Enfin, j’ai expérimenté les pseudopotentiels sur des systèmes moléculaires variés tels que des systèmes organométalliques et des systèmes PI enchevêtrés. Leurs spectres UV ont pu être reproduits correctement en respectant les conditions suivantes : 1) le pseudopotentiel n’est pas lié à un hétéroatome, 2) les cycles PI ne sont pas tordus de plus de quelques degrés. J’ai aussi participé à une étude théorique de réactivité originale de cycloaddition intramoléculaire (2+2+3) dirigée par le cobaltA pseudopotential method for replacing small hydrocarbon fragments in molecular quantum chemistry calculations is derived and tested. These fragments contain only one or two explicitly-treated electrons. The first is an sp2 carbon atom fragment optimised on ethylene. This potential is found to transfer well to all-trans-polyene and PAH systems, reproducing the HOMO and 1st ionisation and excitation energies to within around 20 % of all-electron DFT calculations. Additional pseudopotentials are created for other sp2 and sp3 hybridised carbon-based fragments. They are able to form bonds with all-electron atoms, and are also found to transfer well to larger systems, provided the systems with which they interact are similar enough to those on which they were optimised. The pseudopotentials are found to be able accurately to reproduce molecular UV and ECD spectra, and are tested on a variety of larger and more complex systems including helicenes, nanotubes and a metallocomplex. A program for the optimisation of these pseudopotentials is developed in Python, which is able to extract pseudopotentials from a variety of all-electron reference criteria.Unrelated to the above, the effects of a lactone group on a particular cobalt-mediated cycloaddition are also examine

Pseudopotential‐fragment spectroscopy for organic molecules and carbon allotropes

International audienceFollowing on from a previous work (Punter et al., IJQC 2019, 119, 23), pseudopotential sets are developed and tested for a variety of sp 2 and sp 3 carbon fragments. These fragments contain only one or two explicit protons and electrons, and make use of non-atom-centered potentials. They are tested with density functional theory calculations in a selection of chemical environments in which several physical characteristics , including orbital and first ionization energies, are found to be well reproduced. They are then employed in the reproduction of molecular absorption spectra for large organic molecules and carbon allotropes, and are found to recreate both absorption and electronic circular dichroism spectra to a high accuracy. They are also found significantly to increase the computational efficiency of time dependent density functional theory (TDDFT) calculations in which they are used

Mechanistic insight into cobalt-mediated [2 + 2 + 2]-cycloaddition reactions with γ-alkylidenebutenolide and γ-alkylidenebuterolactam as 2π partners

The molecular complexity of recently reported cobalt(III) polycyclic complexes, resulting from an intramolecular formal (2 + 2 + 3) cycloaddition reaction on an enediyne containing a lactone moiety, has prompted us to computationally review the mechanisms of cobalt cycloaddition reactions with γ-alkylidenebutenolide or γ-alkylidenebuterolactam as 2π partners. Computed mechanisms are compared, leading to either cobalt(III)- or cobalt(I)-spiro complexes depending of both the nature of the reaction (intra- vs. intermolecular pathway) and the nature of the 2π partner (γ-alkylidenebutenolide vs. γ-alkylidenebuterolactam). These proposed mechanisms are supported by experiments, allowing us to report the synthesis and characterization of the predicted compounds

When cobalt-mediated [2 + 2 + 2] cycloaddition reaction dares go astray: synthesis of unprecedented cobalt( iii )-complexes

International audienceIn sharp contrast with the standard [2 + 2 + 2] cycloaddition reaction of diyne/ene, cobalt-mediated cycloadditions with γ-alkylidenebutenolide led to unprecedented cobalt(III) polycyclic complexes. A plausible mechanism supported by a computational study based on an unusual fragmentation of the butenolide moiety was postulated to account for this original reaction. The transition metal-catalyzed [2 + 2 + 2] cycloaddition reaction is well established as one of the most elegant methods for the rapid construction of functionalised aromatic and hetero-aromatic polycyclic compounds, as well as 1,3-cyclohexadiene derivatives. Since the original report of a metal-mediated [2 + 2 + 2] cycloaddition reaction of acetylene derivatives, 1 many groups have demonstrated the significance of this reaction through the use of various transition metal complexes, mainly from group 8-10 elements (Ir, Ru, Ni, Fe, Co, Rh, Nb the most employed). 2 Among all the available catalysts, CpCoL 2 complexes (L = CO, PR 3 , alkenes) have been frequently employed as an active source of "CpCo". Such systems have proved their efficiency (i) for the co-cyclisation of alkynes with alkenes to give cyclohexadiene products 1 in their complexed form, 2a (ii) for the linear 2 : 1 co-oligomerisation 3 of alkynes with acyclic enol ethers (R 3 = alkoxyl) to give 1-alkoxy-1,3,5-triene derivatives 2 (Scheme 1a). It is worth noting that the use of cyclic enol ethers such as 2,3-dihydrofuran produced unconju-gated 1,3,6-trienes 3 whereas benzofuran derivatives led to the formation of the corresponding CpCo-complexed cyclohexa-dienes. 4 Herein, we report the development of a cobalt-mediated polycyclisation reaction with the original enediynes 3 bearing an alkylidenebutenolide moiety. Compared to "classic" alkenes as well as "classic" enol ethers, alkylidene-butenolides display a unique exo-cyclic double bond. This double bond, which was never been used as 2π partner in intra-or intermolecular [2 + 2 + 2] cycloaddition reactions, could have two distinct electronic properties due to the cyclic enol acetate and γ,δ-unsaturated lactone moieties. This speci-ficity would account for the unusual reactivity (Scheme 1b and c). The main features of the present work include (i) formal (2 + 2 + 3) cycloaddition reaction, (ii) unprecedented formation of cobalt(III) complexes 4 featuring both π-allyl and carbanion ligands (highlighted in green in Scheme 1c) and (iii) high levels of regio-and diastereoselectivities. These cobalt(III) complexes rearranged in acidic conditions to give bicyclo[3.3.1] non-3-en-2-one scaffolds found in polyprenylated acylphloro-glucinol natural products. Furthermore, a mechanism pathway, supported by a computational approach, based on Scheme 1 Outcomes of cobalt(I)-mediated process. † Electronic supplementary information (ESI) available: Synthesis procedures, 1 H and 13 C NMR spectra of each compounds and computational studies. CCDC 1853760, 1853762, 1853766 and 1853778. For ESI and crystallographic data in CIF or other electronic format se