DFT Investigation of the Stereoselectivity of the Lewis-Acid-Catalyzed Diels-Alder Reaction between 2,5-Dimethylfuran and Acrolein.

Density functional theory (DFT) has been enacted to study the Diels-Alder reaction between 2,5-dimethylfuran (2,5-DMF), a direct product of biomass transformation, and acrolein and to analyze its thermodynamics, kinetics, and mechanism when catalyzed by a Lewis acid (LA), in comparison to the uncatalyzed reaction. The uncatalyzed reaction occurs via a typical one-step asynchronous process, corresponding to a normal electron demand (NED) mechanism, where acrolein is an electrophile whereas 2,5-DMF is a nucleophile. The small endo selectivity in solvents of low dielectric constants is replaced by a small exo selectivity in solvents with larger dielectric constants, such as DMSO.

Unveiling the Reaction Mechanism of Diels-Alder Cycloadditions between 2,5-Dimethylfuran and Ethylene Derivatives Using Topological Tools.

The [4+2] Diels-Alder cycloaddition reaction between 2,5-DMF (1) and ethylene derivatives (2a-h) activated by electron-withdrawing groups has been studied at the density functional theory levels using a panoply of tools to unravel the reaction mechanisms. From the analysis of the reactivity indices, 2a-h behave as electrophiles while 1 as nucleophile, and the activation of the double bond of ethylene increases its electrophilicity, which is accompanied by an enhancement of the polarity of the reaction. The activation Gibbs free energy decreases linearly as a function of this increase of polarity, as estimated by the electrophilicity difference between the reactants.

Vibronic Structure of the UV/Visible Absorption Spectra of Phenol and Phenolate: A Hybrid Density Functional Theory─Doktorov's Quantum Algorithm Approach.

The Doktorov's quantum algorithm has been enacted in combination with time-dependent density functional theory (TD-DFT) to simulate the vibronic structure of the UV/visible absorption spectra of the phenol and phenolate molecules. On the one hand, DFT and TD-DFT are employed with classical algorithms to calculate the ground and excited-state electronic structures as well as their vibrational frequencies and normal modes, whereas, on the other hand, quantum algorithms are employed for evaluating the vibrational transition intensities. In comparison to a previous study, , 128, 4369-4377, which demonstrated Doktorov's quantum algorithm as a proof of concept to predict the vibronic structure of ionization spectra, it is applied here to medium-size molecules with more than 30 vibrational normal modes, without accounting for Duschinsky rotations due to software limitations.

Solvent effects on the second harmonic responses of donor-acceptor Stenhouse adducts: from implicit to hybrid solvation models.

The effect of conformational dynamics and solvent interactions on the second-order nonlinear optical (NLO) responses of the open and closed forms of a donor-acceptor Stenhouse adduct (DASA) are investigated by a mixed quantum/classical computational approach, which couples molecular dynamics (MD) simulations and time-dependent density functional theory (TD-DFT) calculations. The latter are further combined with various solvation schemes, including polarizable continuum models, hybrid QM/MM approaches using either non polarizable or polarizable electrostatic embedding, and QM/QM' schemes with explicit treatment of a few molecules of the first solvation shell. The performances of the different solvation models are discussed in the context of comparisons with experimental data obtained from hyper-Rayleigh scattering measurements.