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

Revealing the Polarizability of Organic Fluorine in the Trifluoromethyl Group: Implications in Supramolecular Chemistry

The experimental evidence for the polarization of the electron density on the fluorine atom of the trifluoromethyl group in the crystal results in the formation of an electron deficient region. This facilitates F···F halogen bond formation along with the subsequent presence of “short” C–H···F intermolecular contacts (rare geometry) which are a significant electronic and structural feature. This study proves that such an interaction has a substantial “electrostatic contribution”. It breaks the long-accepted lore that “organic fluorine is not polarizable”

Revealing the Polarizability of Organic Fluorine in the Trifluoromethyl Group: Implications in Supramolecular Chemistry

The experimental evidence for the polarization of the electron density on the fluorine atom of the trifluoromethyl group in the crystal results in the formation of an electron deficient region. This facilitates F···F halogen bond formation along with the subsequent presence of “short” C–H···F intermolecular contacts (rare geometry) which are a significant electronic and structural feature. This study proves that such an interaction has a substantial “electrostatic contribution”. It breaks the long-accepted lore that “organic fluorine is not polarizable”

Structural Insights into Proton Conduction in Gallic Acid–Isoniazid Cocrystals

Hydrated cocrystal of gallic acid–isoniazid displays a single crystal-to-single crystal transformation upon dehydration, resulting in a difference of three orders of magnitude in proton conduction. The conduction pathway is shown to follow the Grotthus mechanism, supported by theoretical (DFT) calculations

Crystal Structures and Physicochemical Properties of Four New Lamotrigine Multicomponent Forms

In the present study, four new multicomponent forms of lamotrigine (LTG) with selected carboxylic acids, viz. acetic acid, propionic acid, sorbic acid, and glutaric acid, have been identified. Preliminary solid-state characterization was done by differential scanning calorimetry/thermogravimetric, infrared, and powder X-ray diffraction techniques. X-ray single-crystal structure analysis confirmed the proton transfer, stoichiometry, and the molecular composition, revealing all of these to be a new salt/salt-cocrystal/salt monosolvate monohydrate of LTG. All four compounds exhibited both the aminopyridine dimer of LTG (motif 4) and cation–anion dimers between protonated LTG and the carboxylate anion in their crystal structures. Further, these new crystal forms were subjected to solubility studies in water, powder dissolution studies in 0.1 N HCl, and stability studies under humid conditions in comparison with pure LTG base. The solubility of these compounds in water is significantly enhanced compared with that of pure base, which is attributed to the type of packing motifs present in their crystal structures as well as to the lowering of the pH by the acidic coformers. Solid residues of all forms remaining after solubility and dissolution experiments were also assessed for any transformation in water and acidic medium

Tautomeric Preference and Conformation Locking in Fenobam, Thiofenobam, and Their Analogues: The Decisive Role of Hydrogen Bond Hierarchy

The crystal and molecular structures of the potential antidepressant drug fenobam and its derivatives are examined in terms of the preferred form among the two possible tautomeric structures. In this study, chemical derivatization has been utilized as a means to “experimentally simulate” the tautomeric preference and conformational variability in fenobam. Eight new derivatives of fenobam have been synthesized, and structural features have been characterized by single-crystal X-ray diffraction and NMR spectroscopy. The specific tautomeric preference found in all of these compounds and their known crystal forms have been construed in terms of the stabilizing intramolecular N–H···O and N–H···S hydrogen bonding. The hierarchy of intramolecular hydrogen bonds evidenced as the preference of the C–H···O hydrogen bond over C–H···N and that of the C–H···N hydrogen bond over C–H···S explains the two distinct conformations adopted by fenobam and thiofenobam derivatives. The relative energy values of different molecular conformations have been calculated and compared

Crystal Structures and Physicochemical Properties of Four New Lamotrigine Multicomponent Forms

In the present study, four new multicomponent forms of lamotrigine (LTG) with selected carboxylic acids, viz. acetic acid, propionic acid, sorbic acid, and glutaric acid, have been identified. Preliminary solid-state characterization was done by differential scanning calorimetry/thermogravimetric, infrared, and powder X-ray diffraction techniques. X-ray single-crystal structure analysis confirmed the proton transfer, stoichiometry, and the molecular composition, revealing all of these to be a new salt/salt-cocrystal/salt monosolvate monohydrate of LTG. All four compounds exhibited both the aminopyridine dimer of LTG (motif 4) and cation–anion dimers between protonated LTG and the carboxylate anion in their crystal structures. Further, these new crystal forms were subjected to solubility studies in water, powder dissolution studies in 0.1 N HCl, and stability studies under humid conditions in comparison with pure LTG base. The solubility of these compounds in water is significantly enhanced compared with that of pure base, which is attributed to the type of packing motifs present in their crystal structures as well as to the lowering of the pH by the acidic coformers. Solid residues of all forms remaining after solubility and dissolution experiments were also assessed for any transformation in water and acidic medium

A Donor–Acceptor–Donor Structured Organic Conductor with S···S Chalcogen Bonding

A novel thiophene derivative 7,9-di­(thiophen-2-yl)-8<i>H</i>-cyclopenta­[a]­acenaphthylen-8-one (DTCPA) is shown to exhibit high electrical conductivity (1.97 × 10^–2 ± 0.0018 S/cm at RT) in the crystalline state. The material shows two orders of increase in conductivity from normal solid to single crystalline state. The crystal structure has S···S chalcogen bonding, C–H···O hydrogen bonding, and π···π stacking as the major intermolecular interactions. The nature and strength of the S···S interactions in this structure have been evaluated by theoretical charge density analysis, and its contribution to the crystal packing quantified by Hirshfeld surface analysis. Further, thermal and morphological characterizations have been carried out, and the second harmonic generation (SHG) efficiency has been measured using the Kurtz–Perry method