: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Polycyclic Hydrocarbons Vol. 1. Pp. xxvi + 487. 126S. (With a chapter on carcinogenesis by Regina Schoental.) Vol. 2. Pp. lvii + 487. 140s. By E. Clar. (London and New York: Academic Press; Berlin: Springer-Verlag, 1964.)

Polycyclic Aromatic Hydrocarbons

Hydrogels are polymer networks infiltrated with water. Many biological hydrogels in animal bodies such as muscles, heart valves, cartilages, and tendons possess extreme mechanical properties including being extremely tough, strong, resilient, adhesive, and fatigue-resistant. These mechanical properties are also critical for hydrogels' diverse applications ranging from drug delivery, tissue engineering, medical implants, wound dressings, and contact lenses to sensors, actuators, electronic devices, optical devices, batteries, water harvesters, and soft robots. Whereas numerous hydrogels have been developed over the last few decades, a set of general principles that can rationally guide the design of hydrogels using different materials and fabrication methods for various applications remain a central need in the field of soft materials. This review is aimed at synergistically reporting: (i) general design principles for hydrogels to achieve extreme mechanical and physical properties, (ii) implementation strategies for the design principles using unconventional polymer networks, and (iii) future directions for the orthogonal design of hydrogels to achieve multiple combined mechanical, physical, chemical, and biological properties. Because these design principles and implementation strategies are based on generic polymer networks, they are also applicable to other soft materials including elastomers and organogels. Overall, the review will not only provide comprehensive and systematic guidelines on the rational design of soft materials, but also provoke interdisciplinary discussions on a fundamental question: why does nature select soft materials with unconventional polymer networks to constitute the major parts of animal bodies?

Soft Materials by Design: Unconventional Polymer Networks Give Extreme Properties.

N-Heterocyclic carbenes (NHC) are nowadays ubiquitous and indispensable in many research fields, and it is not possible to imagine modern transition metal and main group element chemistry without t...

N-Heterocyclic Carbene Adducts of Main Group Elements and Their Use as Ligands in Transition Metal Chemistry.

https://hal-univ-rennes1.archives-ouvertes.fr/hal-01282461/document

Metal-Catalyzed Azide-Alkyne “Click” Reactions: Mechanistic Overview and Recent Trends

Cumulenes, including allene, ketenimine, and ketene, can be employed as dienophiles in Diels–Alder type reactions. The activation energies of a Diels–Alder reaction between cyclopentadiene and either the C═C bond or the other C═X (X = C, N, or O) bond in cumulenes have been calculated by G3B3, CBS-QB3, M06-2X, and B3LYP methods. The reactivity trend for the C═C bond in cumulenes is allene > ketenimine > ketene and that of the C═X bond in cumulenes is ketene > allene > ketenimine. Application of distortion-interaction analysis only at transition states does not give a satisfactory explanation for these reactivities. By employing distortion-interaction analysis along reaction pathways, we found that the reactivity of the C═C and C═X bond in cumulenes is controlled by both of its distortion and interaction energies. The lowest distortion energy of allene leads to its highest reactivity; the higher interaction energy results in higher activation energy of ketene than that of ketenimine. Compared with the reac...

Reactivity for the Diels–Alder Reaction of Cumulenes: A Distortion-Interaction Analysis along the Reaction Pathway

Density functional theory (DFT) method B3LYP with a dispersion term (B3LYP-D3BJ) has been used to clarify the regioselectivity of zinc mediated 1,3-dipolar cycloaddition of azides and alkynes. Computational results indicate that the dipolar cycloaddition takes place via a concerted five-membered-ring transition state, leading to a 1,5-disubstituted 1,2,3-triazole product, which is consistent with the experiment reported by Greaney's group. The coordination of imidazole ligand to zinc is reversible, and the regioselectivity is irrelevant to the coordination of imidazole ligand. Moreover, substituent effect of alkynes has also been studied. Finally, distortion–interaction analysis along the reaction pathways and frontier molecular orbital theory are used to explain the reactivity and 1,5-regioselectivity.

Mechanism and selectivity for zinc-mediated cycloaddition of azides with alkynes: a computational study

Theoretical study of the electron-donating effects of thiourea ligands in catalysis

Chromium fragments coordinated with graphene provide a potentially powerful method for the modification of graphene. The newly reported density functional theory method, M11-L, was employed to elucidate the coordination of chromium fragments with graphene. Oligoacenes were chosen to model graphene. The radii of the centrosymmetric oligoacenes were systematically increased to find the limit required to model graphene. meta-Trisubstituted benzene coordinated chromium fragments were employed to study the electronic effect of the complexation of chromium with graphene. The movement and arrangement of the chromium fragments on graphene is also studied.

Yu Lei

Papers

Reactivity for the Diels–Alder Reaction of Cumulenes: A Distortion-Interaction Analysis along the Reaction Pathway

Mechanism and selectivity for zinc-mediated cycloaddition of azides with alkynes: a computational study

Theoretical study of the electron-donating effects of thiourea ligands in catalysis

Hexahapto-chromium complexes of graphene: a theoretical study