Stereoelectronic interactions are too weak to explain the molecular conformation in solid state of -2--butyl-5-(-butylsulfonyl)-1,3-dioxane.

-2--Butyl-5-(-butylsulfonyl)-1,3-dioxane (-1) exhibits a high degree of eclipsing in the H-C5-S-C segment in the solid state, the origin of which remains unexplained. The eclipsed conformation that corresponds to an energetic minimum in the solid state practically corresponds to a rotational transition state in solution, which allows an approach to understand transitions states. The difference in the enthalpy of sublimation Δ between -1 and the more stable -1 is 8.

Formation of the quasi-planar B boron cluster: topological path from B and disk aromaticity.

Formation and stability of the B boron cluster were investigated using a topological approach and the disk aromaticity model. An extensive global energy minimum search for the B system which was carried out by means of the Mexican Enhanced Genetic Algorithm (MEGA) in conjunction with density functional theory computations, confirms a quasi-planar structure as its energetically most stable isomer. Such a structural motif is derived by applying a topological leapfrog operation to a B form.

Triangulenes and theirs ions: reaching the limits of Clar's rule.

The triangulenes and their closed-shell ions are a family of polycyclic aromatic hydrocarbons (PAH) that have possible applications in fields as different as spintronics or catalysis. However, the electron delocalization in such systems is not well understood because there are several differences to classical PAHs. We found that the triangulene cations are always more delocalized than the radicals or the anions, independently of the π e count.

How to Bend a Cumulene.

Allenes (carbodicarbenes) and [3]cumulenes are linear carbon chains that can be bent when the terminal group has a strong carbene nature. This bending can be quite pronounced in allenes but not in [3]cumulenes. In this study, how N-heterocyclic or cyclic (alkyl)(amino) carbene (NHC and CAAC, respectively) terminal groups can modify the linear structure of [n]cumulenes has been analyzed.

Origin of the Photoinduced Geometrical Change of Copper(I) Complexes from the Quantum Chemical Topology View.

Copper(I) complexes (CICs) are of great interest due to their applications as redox mediators and molecular switches. CICs present drastic geometrical change in their excited states, which interferes with their luminescence properties. The photophysical process has been extensively studied by several time-resolved methods to gain an understanding of the dynamics and mechanism of the torsion, which has been explained in terms of a Jahn-Teller effect.

Are boat transition states likely to occur in Cope rearrangements? A DFT study of the biogenesis of germacranes.

It has been proposed that elemanes are biogenetically formed from germacranes by Cope sigmatropic rearrangements. Normally, this reaction proceeds through a transition state with a chair conformation. However, the transformation of schkuhriolide (germacrane) into elemanschkuhriolide (elemane) may occur through a boat transition state due to the final configuration of the elemanschkuhriolide, but this transition state is questionable due to its high energy.

Delocalized and localized donating-accepting Mn-C interactions in half-sandwich cyclopentadienyl and pentadienyl complexes.

The widely used cyclopentadienyl (Cp) ligand and the pentadienyl (Pdl) ligand have very similar molecular orbitals (MOs) but they have significantly different chemical behavior. The extensively mixing of the MOs in the Pdl ligand has prevented a quantitative explanation of the observed differences between these two ligands. In a series of synthesized close/open half sandwich manganese phosphine carbonyls, the quantum theory of atoms in molecules and the interacting quantum atom model allow us to quantify the accepting-donating capacities of both ligands and to break down the M-dienyl bond into individual atomic interactions.

Torquoselectivity in Cyclobutene Ring Openings and the Interatomic Interactions That Control Them.

Torquoselectivity has explained diasteromeric preferences of a number electrocyclic ring openings. The quantum theory of atoms in molecules (QTAIM), the electron localizability indicator (ELI-D), and the interacting quantum atoms (IQA) energy partition method are used to evaluate qualitatively and quantitatively the atomic interactions behind the torquoselectivity of a series of 3-substituted cyclobutenes. ELI-D topology and IQA energies show that the interaction between the distal terminus carbon atom of cyclobutene (C4) with the substituent at C3 (R5) in the transition state governs torquoselectivities.

A unifying bonding concept for metal hydrosilane complexes.

Experimental and theoretical charge density studies and molecular orbital analyses suggest that the complexes [Cp2Ti(PMe3)SiH2Ph2] (1) and [Cp2Ti(PMe3)SiHCl3] (2) display virtually the same electronic structures. No evidence for a significant interligand hypervalent interaction could be identified for 2. A bonding concept for transition-metal hydrosilane complexes aims to identify the true key parameters for a selective activation of the individual M-Si and Si-H bonds.

On the chemical shifts of agostic protons.

Agostic hydrogen atoms in planar d(8) transition metal complexes display a remarkable wide range of chemical shifts from +5 to -10 ppm in the proton NMR spectra. It is therefore surprising that a simple recipe can be elaborated to predict the influence of the local electronic structure of the metal atom on the shielding of the coordinating protons: In cases where the agostic hydrogen atom is pointing to a local Lewis acidic center at the metal the (1)H NMR signal is shifted upfield relative to the scenario where the proton is opposing a local charge concentration at the metal. To trace the physical origin of this empirical relationship, a systematic study has been performed to understand how the (i) topology of the electron density and (ii) orientation of the magnetic field vector, B0, control the paratropic or diatropic characteristics of the induced current density at the metal atom and thus the shielding or deshielding of the agostic protons.

Biogenesis of sesquiterpene lactones pseudoguaianolides from germacranolides: theoretical study on the reaction mechanism of terminal biogenesis of 8-epiconfertin.

The fundamental study of the biogenetic origin of natural products has always been limited from the experimental point of view because proposed reaction mechanisms have only been supported on the molecular structures of reagents and the reaction products. In a seminal contribution, Ortega and Maldonado (Ortega, A.; Maldonado, E.