Exploring Cyclopentadienone Antiaromaticity: Charge Density Studies of Various Tetracyclones

A systematic study of six tetracyclones has been carried out using experimental and theoretical charge density analysis. A three pronged approach based on quantum theory of atoms in molecules (QTAIM), nucleus independent chemical shifts (NICS) criterion, and source function (SF) contributions has been performed to establish the degree of antiaromaticity of the central five-membered ring in all the derivatives. Electrostatic potentials mapped on the isodensity surface show that electron withdrawing substituents turn both C and O atoms of the carbonyl group more electropositive while retaining the direction of polarity

Exploring Cyclopentadienone Antiaromaticity: Charge Density Studies of Various Tetracyclones

A systematic study of six tetracyclones has been carried out using experimental and theoretical charge density analysis. A three pronged approach based on quantum theory of atoms in molecules (QTAIM), nucleus independent chemical shifts (NICS) criterion, and source function (SF) contributions has been performed to establish the degree of antiaromaticity of the central five-membered ring in all the derivatives. Electrostatic potentials mapped on the isodensity surface show that electron withdrawing substituents turn both C and O atoms of the carbonyl group more electropositive while retaining the direction of polarity

Exploring Cyclopentadienone Antiaromaticity: Charge Density Studies of Various Tetracyclones

A systematic study of six tetracyclones has been carried out using experimental and theoretical charge density analysis. A three pronged approach based on quantum theory of atoms in molecules (QTAIM), nucleus independent chemical shifts (NICS) criterion, and source function (SF) contributions has been performed to establish the degree of antiaromaticity of the central five-membered ring in all the derivatives. Electrostatic potentials mapped on the isodensity surface show that electron withdrawing substituents turn both C and O atoms of the carbonyl group more electropositive while retaining the direction of polarity

Characterization of Interactions Involving Bromine in 2,2-Dibromo-2,3-dihydroinden-1-one via Experimental Charge Density Analysis

Experimental and theoretical charge density analyses on 2,2-dibromo-2,3-dihydroinden-1-one have been carried out to quantify the topological features of a short C–Br···O halogen bond with nearly linear geometry (2.922 Å, ∠C–Br···O = 172.7°) and to assess the strength of the interactions using the topological features of the electron density. The electrostatic potential map indicates the presence of the “σ-hole” on bromine, while the interaction energy is comparable to that of a moderate O–H···O hydrogen bond. In addition, the energetic contribution of C–H···Br interaction is demonstrated to be on par with that of the C–Br···O halogen bond in stabilizing the crystal structure

SF₅‑Enolates in Ti(IV)-Mediated Aldol Reactions

The F···Ti bonding in the transition structures determines high <i>trans</i>- and <i>syn</i>-diastereoselectivities for aldol reactions of SF₅-acetates with aldehydes in the presence of TiCl₄ in the non-nucleophilic solvent CH₂Cl₂. Such bonding is canceled in nucleophilic solvents where opposite <i>cis</i>-stereochemistry is observed. The potential of thus obtained stereoisomeric SF₅-aryl acrylates as dipolarophiles in the preparation of SF₅-containing heterocycles is demonstrated

SF₅‑Enolates in Ti(IV)-Mediated Aldol Reactions

The F···Ti bonding in the transition structures determines high <i>trans</i>- and <i>syn</i>-diastereoselectivities for aldol reactions of SF₅-acetates with aldehydes in the presence of TiCl₄ in the non-nucleophilic solvent CH₂Cl₂. Such bonding is canceled in nucleophilic solvents where opposite <i>cis</i>-stereochemistry is observed. The potential of thus obtained stereoisomeric SF₅-aryl acrylates as dipolarophiles in the preparation of SF₅-containing heterocycles is demonstrated

SF₅‑Enolates in Ti(IV)-Mediated Aldol Reactions

The F···Ti bonding in the transition structures determines high <i>trans</i>- and <i>syn</i>-diastereoselectivities for aldol reactions of SF₅-acetates with aldehydes in the presence of TiCl₄ in the non-nucleophilic solvent CH₂Cl₂. Such bonding is canceled in nucleophilic solvents where opposite <i>cis</i>-stereochemistry is observed. The potential of thus obtained stereoisomeric SF₅-aryl acrylates as dipolarophiles in the preparation of SF₅-containing heterocycles is demonstrated

SF₅‑Enolates in Ti(IV)-Mediated Aldol Reactions

The F···Ti bonding in the transition structures determines high <i>trans</i>- and <i>syn</i>-diastereoselectivities for aldol reactions of SF₅-acetates with aldehydes in the presence of TiCl₄ in the non-nucleophilic solvent CH₂Cl₂. Such bonding is canceled in nucleophilic solvents where opposite <i>cis</i>-stereochemistry is observed. The potential of thus obtained stereoisomeric SF₅-aryl acrylates as dipolarophiles in the preparation of SF₅-containing heterocycles is demonstrated

Temperature-Induced Reversible First-Order Single Crystal to Single Crystal Phase Transition in Boc‑γ⁴(<i>R</i>)Val-Val-OH: Interplay of Enthalpy and Entropy

Crystals of Boc-γ⁴(<i>R</i>)­Val-Val-OH undergo a reversible first-order single crystal to single crystal phase transition at <i>T</i>_c ≈ 205 K from the orthorhombic space group <i>P</i>22₁2₁ (<i>Z</i>′ = 1) to the monoclinic space group <i>P</i>2₁ (<i>Z</i>′ = 2) with a hysteresis of ∼2.1 K. The low-temperature monoclinic form is best described as a nonmerohedral twin with ∼50% contributions from its two components. The thermal behavior of the dipeptide crystals was characterized by differential scanning calorimetry experiments. Visual changes in birefringence of the sample during heating and cooling cycles on a hot-stage microscope with polarized light supported the phase transition. Variable-temperature unit cell check measurements from 300 to 100 K showed discontinuity in the volume and cell parameters near the transition temperature, supporting the first-order behavior. A detailed comparison of the room-temperature orthorhombic form with the low-temperature (100 K) monoclinic form revealed that the strong hydrogen-bonding motif is retained in both crystal systems, whereas the non-covalent interactions involving side chains of the dipeptide differ significantly, leading to a small change in molecular conformation in the monoclinic form as well as a small reorientation of the molecules along the <i>ac</i> plane. A rigid-body thermal motion analysis (translation, libration, screw; correlation of translation and libration) was performed to study the crystal entropy. The reversible nature of the phase transition is probably the result of an interplay between enthalpy and entropy: the low-temperature monoclinic form is enthalpically favored, whereas the room-temperature orthorhombic form is entropically favored

Temperature-Induced Reversible First-Order Single Crystal to Single Crystal Phase Transition in Boc‑γ⁴(<i>R</i>)Val-Val-OH: Interplay of Enthalpy and Entropy

Crystals of Boc-γ⁴(<i>R</i>)­Val-Val-OH undergo a reversible first-order single crystal to single crystal phase transition at <i>T</i>_c ≈ 205 K from the orthorhombic space group <i>P</i>22₁2₁ (<i>Z</i>′ = 1) to the monoclinic space group <i>P</i>2₁ (<i>Z</i>′ = 2) with a hysteresis of ∼2.1 K. The low-temperature monoclinic form is best described as a nonmerohedral twin with ∼50% contributions from its two components. The thermal behavior of the dipeptide crystals was characterized by differential scanning calorimetry experiments. Visual changes in birefringence of the sample during heating and cooling cycles on a hot-stage microscope with polarized light supported the phase transition. Variable-temperature unit cell check measurements from 300 to 100 K showed discontinuity in the volume and cell parameters near the transition temperature, supporting the first-order behavior. A detailed comparison of the room-temperature orthorhombic form with the low-temperature (100 K) monoclinic form revealed that the strong hydrogen-bonding motif is retained in both crystal systems, whereas the non-covalent interactions involving side chains of the dipeptide differ significantly, leading to a small change in molecular conformation in the monoclinic form as well as a small reorientation of the molecules along the <i>ac</i> plane. A rigid-body thermal motion analysis (translation, libration, screw; correlation of translation and libration) was performed to study the crystal entropy. The reversible nature of the phase transition is probably the result of an interplay between enthalpy and entropy: the low-temperature monoclinic form is enthalpically favored, whereas the room-temperature orthorhombic form is entropically favored