Reaction of Paramagnetic Synthon,Lithiated 4,4,5,5‐Tetramethyl‐4,5‐dihydro‐1H‐imidazol‐1‐oxyl 3‐oxide,with Cyclic Aldonitrones of the Imidazole Series

It was shown that dipole‐stabilized paramagnetic carbanion lithiated 4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazol‐1‐oxyl 3‐oxide can be attached in a nucleophilic manner to either isolated or conjugated aldonitrones of the 2,5‐dihydroimidazole 3‐oxide and 2H‐imidazole 1‐oxide series to afford adducts the subsequent oxidation of which leads to polyfunctional mono‐ and diradicals. According to XRD, at least two polymorphic modifications can be formed during crystallization of the resulting paramagnetic compounds, and for each of them, geometric parameters of the molecules are similar. An EPR spectrum of the diradical in frozen toluene has a complicated lineshape, which can be fairly well reproduced by using X‐ray diffraction structural analysis and the following set of parameters: D=14.9 mT, E=1.7 mT; tensor a(¹⁴N)=[0.260 0.260 1.625] mT, two equivalent tensors for the nitronyl nitroxide moiety a(¹⁴N)=[0.198 0.198 0.700] mT, and g≈2.007. According to our DFT and ab initio calculations, the intramolecular exchange in the diradical is very weak and most likely ferromagnetic.     

Synthesis and molecular structures of 1‐chloro‐1‐silacyclopent‐2‐enes. Combination of 1,2‐hydroboration, 1,1‐organoboration and protodeborylation

The reaction of alkyn‐1‐yl(chloro)(methyl)vinyl‐ and alkyn‐1‐yl(chloro)(phenyl)‐vinylsilane with 9‐borabicyclo[3.3.1]nonane (9‐BBN) afforded selectively 1‐silacyclopent‐2‐ene derivatives containing a Si? Cl function, as a result of consecutive 1,2‐hydroboration and 1,1‐organoboration. Protodeborylation with acetic acid left the Si? Cl functions in various 1‐silacyclopent‐2‐enes untouched, whereas acetic acid in the presence of dipropylamine led to conversion of the Si? Cl into the Si? OAc function. New starting materials and all products were characterized in solution by multinuclear NMR spectroscopy (¹H, ¹¹B, ¹³C and ²⁹Si NMR), and the molecular structures of two 1‐silacyclopent‐2‐ene derivatives were determined by X‐ray analysis. The gas phase geometries of 1‐silacyclopent‐2‐enes were optimized by DFT calculations [B3LYP/6‐311 + G(d,p) level of theory], found to be in reasonable agreement with the results of the crystal structure determination, and NMR parameters were calculated at the same level of theory. Copyright © 2009 John Wiley & Sons, Ltd.     

Polymorphism of methyl 4‐amino‐3‐phenylisothiazole‐5‐carboxylate: an experimental and theoretical study

Being a close analogue of amflutizole, methyl 4‐amino‐3‐phenylisothiazole‐5‐carboxylate (C₁₁H₁₀N₂O₂S) was assumed to be capable of forming polymorphic structures. Noncentrosymmetric and centrosymmetric polymorphs have been obtained by crystallization from a series of more volatile solvents and from denser tetrachloromethane, respectively. Identical conformations of the molecule are found in both structures. The two polymorphs differ mainly in the intermolecular interactions formed by the amino group and in the type of stacking interactions between the π‐systems. The most effective method for revealing packing motifs in structures with intermolecular interactions of different types (hydrogen bonding, stacking, dispersion, etc.) is to study the pairwise interaction energies using quantum chemical calculations. Molecules form a column as the primary basic structural motif due to stacking interactions in both polymorphic structures under study. The character of a column (straight or zigzag) is determined by the orientations of the stacked molecules (in a `head‐to‐head' or `head‐to‐tail' manner). Columns bound by intermolecular N—H…O and N—H…N hydrogen bonds form a double column as the main structural motif in the noncentrosymmetric structure. Double columns in the noncentrosymmetric structure and columns in the centrosymmetric structure interact strongly within the ab crystallographic plane, forming a layer as a secondary basic structural motif. The noncentrosymmetric structure has a lower density and a lower (by 0.59 kJ mol^?1) lattice energy, calculated using periodic calculations, compared to the centrosymmetric structure.     

On the Reaction of Glycerol Dehydratase with But‐3‐ene‐1,2‐diol

Intriguing inactivation : Calculations suggest that the ability of relatively high‐energy radical intermediates to inactivate glycerol dehydratase (GDH) may reflect a general and hitherto unidentified inactivation mechanism in the reaction of coenzyme B₁₂‐dependent enzymes and 3‐unsaturated 1,2‐diols (see scheme; AdoCbl: adenosylcobalamin or coenzyme B₁₂).

     

Ab initio and semiempirical computational studies on 1‐{(2E)‐2‐[(aminocarbonothioyl)hydrazono]‐2‐(3‐mesityl‐3‐methylcyclobutyl)ethyl}‐pyrrolidine‐2,5‐dione

The molecular geometry, vibrational frequencies, and gauge including atomic orbital (GIAO) ¹H‐ and ¹³C NMR chemical shift values of the title compound in the ground state have been calculated using the Hartree‐Fock (HF) and density functional theory (DFT) methods with 6‐31G(d) basis sets, and compared with the experimental data. The calculated results show that the optimized geometries can well reproduce the crystal structural parameters and the theoretical vibrational frequencies, and ¹H‐ and ¹³C NMR chemical shift values show good agreement with experimental data. To determine conformational flexibility, the molecular energy profile of the title compound was obtained by semiempirical (AM1) calculations with respect to the selected torsion angle, which was varied from ?180° to +180° in steps of 10°. The energetic behavior of the title compound in solvent media was examined using the B3LYP method with the 6‐31G(d) basis set by applying the Onsager and the polarizable continuum model (PCM). The results obtained with these methods reveal that the PCM method provided more stable structure than Qnsager's method. By using TD‐DFT method, electronic absorption spectra of the title compound have been predicted and a good agreement with the TD‐DFT method and the experimental one is determined. The predicted nonlinear optical properties of the title compound are much greater than ones of urea. In addition, the molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis, NBO analysis and thermodynamic properties of the title compound were investigated using theoretical calculations. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

2‐(Dinitromethylene)‐1‐nitro‐1, 3‐diazacyclopentane‐Based Energetic Salts

Energetic salts that contain nitrogen‐rich cations and the 2‐(dinitromethyl)‐3‐nitro‐1, 3‐diazacyclopent‐1‐ene anion were synthesized in high yield by direct neutralization reactions. The resulting salts were fully characterized by multinuclear NMR spectroscopy (¹H and ¹³C), vibrational spectroscopy (IR), elemental analysis, density and differential scanning calorimetry (DSC), and elemental analysis. Additionally, the structures of the ammonium ( 1 ) and isopropylideneaminoguanidinium ( 9 ) 2‐(dinitromethyl)‐3‐nitro‐1, 3‐diazacyclopent‐l‐ene salts were confirmed by single‐crystal X‐ray diffraction. Solid‐state ¹⁵N NMR spectroscopy was used as an effective technique to further determine the structure of some of the products. The densities of the energetic salts paired with organic cations fell between 1.50 and 1.79 g · cm^–3 as measured by a gas pycnometer. Based on the measured densities and calculated heats of formation, detonation pressures and velocities were calculated using Explo 5.05 and found to to be 25.2–35.5 GPa and 7949–9004 m · s^–1, respectively, which make them competitive energetic materials.     

An experimental and theoretical approach to the molecular structure of 3‐{[4‐(3‐Methyl‐3‐phenyl‐cyclobutyl)‐thiazol‐2‐yl]‐hydrazono}‐1,3‐dihydro‐ indol‐2‐one

The title molecule, 3‐{[4‐(3‐methyl‐3‐phenyl‐cyclobutyl)‐thiazol‐2‐yl]‐hydrazono}‐1,3‐dihydro‐indol‐2‐one (C₂₂H₂₀N₄O₁S₁), was prepared and characterized by ¹H NMR, ¹³C NMR, IR, UV–visible, and single‐crystal X‐ray diffraction. The compound crystallizes in the monoclinic space group P21 with a = 8.3401(5), b = 5.6976(3), c = 20.8155(14) Å, and β = 95.144(5)°. Molecular geometry from X‐ray experiment and vibrational frequencies of the title compound in the ground state has been calculated using the Hartree–Fock with 6‐31G(d, p) and density functional method (B3LYP) with 6‐31G(d, p) and 6‐311G(d, p) basis sets, and compared with the experimental data. The calculated results show that optimized geometries can well reproduce the crystal structural parameters, and the theoretical vibrational frequencies values show good agreement with experimental data. Density functional theory calculations of the title compound and thermodynamic properties were performed at B3LYP/6‐31G(d, p) level of theory. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Conformational polymorphs of 3‐cyclopropyl‐5‐(3‐methyl‐[1,2,4]triazolo[4,3‐a]pyridin‐7‐yl)‐1,2,4‐oxadiazole

The dipharmacophore compound 3‐cyclopropyl‐5‐(3‐methyl‐[1,2,4]triazolo[4,3‐a]pyridin‐7‐yl)‐1,2,4‐oxadiazole, C₁₂H₁₁N₅O, was studied on the assumption of its potential biological activity. Two polymorphic forms differ in both their molecular and crystal structures. The monoclinic polymorphic form was crystallized from more volatile solvents and contains a conformer with a higher relative energy. The basic molecule forms an abundance of interactions with relatively close energies. The orthorhombic polymorph was crystallized very slowly from isoamyl alcohol and contains a conformer with a much lower energy. The basic molecule forms two strong interactions and a large number of weak interactions. Stacking interactions of the `head‐to‐head' type in the monoclinic structure and of the `head‐to‐tail' type in the orthorhombic structure proved to be the strongest and form stacked columns in the two polymorphs. The main structural motif of the monoclinic structure is a double column where two stacked columns interact through weak C—H…N hydrogen bonds and dispersive interactions. In the orthorhombic structure, a single stacked column is the main structural motif. Periodic calculations confirmed that the orthorhombic structure obtained by slow evaporation has a lower lattice energy (0.97 kcal mol^?1) compared to the monoclinic structure.     

Experimental and quantum chemical calculational studies on N‐[4‐(3‐Methyl‐3‐phenyl‐cyclobutyl)‐thiazol‐2‐yl]‐N′‐pyridin‐3ylmethylene‐hydrazine

The title molecule, N‐[4‐(3‐Methyl‐3‐phenyl‐cyclobutyl)‐thiazol‐2‐yl]‐N′‐pyridin‐3ylmethylene‐ hydrazine (C₂₀ H₂₀ N₄ S₁), was characterized by ¹H‐NMR, ¹³C‐NMR, IR, UV‐visible, and X‐ray determination. In addition to the molecular geometry from X‐ray experiment, the molecular geometry, vibrational frequencies and gauge including atomic orbital ¹H‐ and ¹³C‐NMR chemical shift values of the title compound in the ground state have been calculated using the Hartree‐Fock and density functional method (B3LYP) with 6‐31G(d, p) basis set. The calculated results show that optimized geometries can well reproduce the crystal structural parameters. By using time‐dependent density functional theory method, electronic absorption spectrum of the title compound has been predicted. © 2011 Wiley Periodicals, Inc.     

On the Electrochemistry and Spectroelectrochemistry of Small Model Star‐Shaped Compounds: 1,3,5‐Triaryl‐1‐Methoxybenzenes and 2,4,6‐Triaryl‐1,3,5‐Trimethoxybenzenes

Model structures of 1,3,5‐triarylbenzenes with a substituted benzene core linked to thienyl or 3,4‐ethylenedioxythienyl (EDOT) terminal groups are studied by electrochemical and in situ ESR/UV/Vis/NIR spectroelectrochemical techniques. Oxidative polymerization of the monomers results in C? C coupling of the thiophene moieties in the 5‐position, forming dimeric structures with bithiophene linkers as the first step. Both the doubly charged protonated dimer and the new dimer formed after proton release are studied in detail for 2,4,6‐tris[2‐(3,4‐ethylenedioxythienyl)]‐1‐methoxybenzene. Quite high stability of the doubly charged σ dimer formed on oxidation with unusual redox behavior at the electrode is observed. Density functional calculations of the molecular structure as well as spectroscopic and electronic properties of charged states in 1,3,5‐triarylbenzene derivatives in the monomeric, dimeric, and oligomeric form are presented. The complex spectroelectrochemical response of a thin solid film formed on the electrode surface upon potentiodynamic polymerization indicates the existence of different charge states of oligomeric structures within the solid matrix.     

Studies on [PtCl2]‐ or [AuCl]‐Catalyzed Cyclization of 1‐(Indol‐2‐yl)‐2,3‐Allenols: The Effects of Water/Steric Hindrance and 1,2‐Migration Selectivity

The [PtCl₂]‐ or [AuCl]‐catalyzed reaction of 1‐(indol‐2‐yl)‐2,3‐allenols occurred smoothly at room temperature to afford a series of poly‐substituted carbazoles efficiently. Compared with the [PtCl₂]‐catalyzed process, the [AuCl]‐catalyzed reaction represents a significant advance in terms of the scope and the selectivity. Selective 1,2‐alkyl or aryl migration of the gold carbene intermediate was observed: compared with the methyl group, the isopropyl, cyclopropyl, cyclobutyl, and cyclohexyl groups migrate exclusively; the cyclopropyl group shifts selectively over the ethyl group; the 1,2‐migration of a non‐methyl linear alkyl is faster than methyl group; the phenyl group migrates exclusively over methyl or ethyl group. DFT calculations show that water makes the elimination of H₂O facile requiring a much lower energy and validates the migratory preferences of different alkyl or phenyl groups observed.     

A New Approach to the Design of Neutral 10‐C‐5 Trigonal‐Bipyramidal Carbon Compounds: A “π‐Electron Cap” Effect

DFT (B3LYP, M06‐2X) and MP2 methods are applied to the design of a wide series of the potentially 10‐C‐5 neutral compounds based on 6‐azabicyclotetradecanes: XC¹(YCH₂CH₂CH₂)₃N 1 – 3 , XC¹(YC₆H₄CH₂)₃N 4 – 6 , XC¹[Y(tBuC₆H₃)CH₂]₃N 7 – 9 and carbatranophanes 10 – 25 (X=Me, F, Cl; Y=O, NH, CH₂, SiH₂; Z=O, CH₂, (CH₂)₂, (CH₂)₃). Carbatranophanes 10 – 25 are characterized by a sterical compression of their axial 3c–4e XC¹←N fragment with respect to that in the parent molecules 4 – 6 . A magnitude of the revealed effect depends on a valence surrounding of the central carbon atom C¹, the size and the nature of the side chains (Z) that link the “π‐electron cap” with a tetradecane backbone. This circumstance allowed us to obtain 10‐C‐5 structures with the configuration of the bonds around the C¹ atom, which corresponds to practically an ideal trigonal bipyramid. In these compounds, the values of the covalence ratio χ of approximately 0.6 for the coordination C¹←N contacts with a covalent contribution (atoms in molecules (AIM) and natural bond orbital (NBO)) are record in magnitude. These values lie close to a low limit of the interval of the χ_Si←D change (0.6–0.9) being characteristic of the dative and ionic‐covalent (by nature) Si←D bond (D=N, O) in the known 10‐Si‐5 silicon compounds.     

3,4‐Dithiaphosphole and 3,3′,4,4′‐Tetrathia‐1,1′‐Biphosphole π‐Conjugated Systems: S Makes the Impact

Conjugated systems based on phospholes and 1,1′‐biphospholes bearing 3,4‐ethylenedithia bridges have been prepared using the Fagan–Nugent route. The mechanism of this organometallic route leading to intermediate zirconacyclopentadienes has been investigated by using theoretical calculations. This study revealed that the oxidative coupling leading to zirconacyclopentadienes is favored over oxidative addition within the S? C≡C bond both thermodynamically and kinetically. The impact of the presence of the S atoms on the optical and electrochemical behavior of the phospholes and 1,1′‐biphospholes has been systematically evaluated both experimentally and theoretically. A comparison with their “all‐carbon” analogues is provided. Of particular interest, this comparative study revealed that the introduction of S atoms has an impact on the electronic properties of phosphole‐based conjugated systems. A decrease of the HOMO–LUMO separation and a stabilization of the LUMO level were observed. These general trends are also observed with 1,1′‐biphospholes exhibiting σ–π conjugation. The P atom of the 3,4‐ethylenedithiaphospholes can be selectively oxidized by S₈ or O₂. These P modifications result in a lowering of the HOMO–LUMO separation as well as an increase of the reduction and oxidation potentials. The S atoms of the 3,4‐ethylenedithia bridge of the 2,5‐phosphole have been oxidized using m‐chloroperoxybenzoic acid. The resulting 3,4‐ethylenesulfoxide oxophosphole was characterized by an X‐ray diffraction study. Experimental and theoretical studies show that this novel chemical manipulation results in an increase of the HOMO–LUMO separation and an important decrease of the LUMO level. The electropolymerization of 2‐thienyl‐capped 3,4‐ethylenedithiathioxophosphole and 1,1′‐biphosphole is reported. The impact of the S substituents on the polymer properties is discussed.     

Synthesis,structural analysis,spectral investigations,and DFT calculations of 1‐(3‐amino‐4‐thia‐1,2‐diazaspiro[4.11]hexadec‐2‐en‐1‐yl)ethan‐1‐one

1‐(3‐amino‐4‐thia‐1,2‐diazaspiro[4.11]hexadec‐2‐en‐1‐yl)ethan‐1‐one was synthesized and experimentally characterized by using FT‐IR, ¹H NMR, ¹³C NMR, and UV–Vis spectroscopy. The structure of the compound was confirmed by single‐crystal X‐ray diffraction. In the crystal structure, the molecules are linked by pairs of N‐H⋯N hydrogen bonds, forming centrosymmetric dimers with the graph‐set motif. The water molecule also plays an important role in the stabilization of the crystal structure, bridging the dimers to form a two‐dimensional supramolecular network. The molecular geometry, frontier molecular orbitals, vibrational frequencies, electronic properties, and molecular electrostatic potential were calculated using density functional theory (DFT) with the B3LYP/6‐311G(d,p) basis set. Geometric parameters, vibrational assignments, and electronic properties such as calculated energies, excitation energies, and oscillator strengths were compared with the experimental data, and it was seen that the theoretical results support the experimental parameters.     

Tetramethyl‐m‐benziporphodimethene and Isomeric α,β‐Unsaturated γ‐Lactam Embedded N‐Confused Tetramethyl‐m‐benziporphodimethenes

The condensation reaction of α,α′‐dihydroxy‐1,3‐diisopropylbenzene, pyrrole, and an aldehyde leads to the formation of tetramethyl‐m‐benziporphodimethene and outer α‐pyrrolic carbon oxygenated N‐confused tetramethyl‐m‐benziporphodimethenes containing a γ‐lactam ring in the macrocycle. Two isomers with the carbonyl group of the lactam ring either close to (O‐Up) or away from (O‐Down) the neighboring sp³ meso carbon were synthesized and characterized. The single crystal X‐ray diffraction analysis on the regular and γ‐lactam containing tetramethyl‐m‐benziporphodimethenes showed highly distorted macrocycles for all compounds. For O‐Up and O‐Down isomers, dimeric structures, assembling by intermolecular hydrogen‐bonding interactions through lactam rings, were observed in the solid state. Fitting the concentration dependent chemical shifts of the outer NH proton using the non‐linear regression method give a maximum association constant of 108.9 M ^?1 for the meso 4‐methylcarboxyphenyl substituted O‐Down isomer. The DFT calculations concluded that the O‐Up isomer is energetically more stable, and the keto form is more stable than the enol form.     

Heteroatom‐Guided Torquoselective Olefination of α‐Oxy and α‐Amino Ketones via Ynolates

Ynolates were found to react with α‐alkoxy‐, α‐siloxy‐, and α‐aryloxyketones at room temperature to afford tetrasubstituted olefins with high Z selectivity. Since the geometrical selectivity was determined in the ring opening of the β‐lactone enolate intermediates, the torquoselectivity was controlled by the ethereal oxygen atoms. From experimental and theoretical studies, the high Z selectivity is induced by orbital and steric interactions rather than by chelation. In a similar manner, α‐dialkylamino ketones provided olefins with excellent Z selectivity. These products can be easily converted into multisubstituted butenolides and γ‐butyrolactams in good yield.     

1‐Carboxymethyl‐3‐methyl‐1H‐imidazol‐3‐ium chloride 2‐(3‐methyl‐1H‐imidazol‐3‐ium‐1‐yl)acetate monohydrate: a crystal stabilized by imidazolium zwitterions

The title compound, C₆H₉N₂O₂⁺·Cl⁻·C₆H₈N₂O₂·H₂O, contains one 2‐(3‐methyl‐1H‐imidazol‐3‐ium‐1‐yl)acetate inner salt molecule, one 1‐carboxymethyl‐3‐methyl‐1H‐imidazol‐3‐ium cation, one chloride ion and one water molecule. In the extended structure, chloride anions and water molecules are linked via O—H...Cl hydrogen bonds, forming an infinite one‐dimensional chain. The chloride anions are also linked by two weak C—H...Cl interactions to neighbouring methylene groups and imidazole rings. Two imidazolium moieties form a homoconjugated cation through a strong and asymmetric O—H...O hydrogen bond of 2.472 (2) Å. The IR spectrum shows a continuous D‐type absorption in the region below 1300 cm⁻¹ and is different to that of 1‐carboxymethyl‐3‐methylimidazolium chloride [Xuan, Wang & Xue (2012). Spectrochim. Acta Part A, 96 , 436–443].     

Wasserstoffbrückenbindungen mit Cyanidionen? Die Strukturen von 1,3‐Diisopropyl‐4,5‐dimethylimidazoliumcyanid und 1‐Isopropyl‐3,4,5‐trimethylimidazoliumcyanid

Hydrogen Bonds with Cyanide Ions? The Structures of 1,3‐Diisopropyl‐4,5‐dimethylimidazolium Cyanide and 1‐Isopropyl‐3,4,5‐trimethylimidazolium Cyanide 1,3‐Diisopropyl‐4,5‐dimethylimidazolium cyanide ( 2a ) and 1‐isopropyl‐3,4,5‐trimethylimidazolium cyanide ( 2b ) are obtained from the reaction of the corresponding 2,3‐dihydrodimethylimidazol‐2‐ylidenes ( 1 ) and hydrogen cyanide in excellent yield. Their crystal structure analyses reveal the presence of ion pairs linked by hydrogen bonds. The crystal structure analysis of 2a reveals a near colinear orientation of the C(1)‐H bond axis and the cyanide ion while in 2b this orientation is perpendicular. In both cases, the interionic distances are in the expected range for hydrogen bonds. Ab‐initio calculations of the total energy of the salts 2 indicate small differences in energy between the colinear and perpendicular orientation of the ions as well as between the colinear C‐H···C‐N and C‐H···N‐C orientations. The comparison of calculated and measured ¹³C and ¹⁵N NMR chemical shifts does not allow the distinction between the possible orientations.     

Synthesis,Electronic Properties,and Reactivity of Phospholes and 1,1′‐Biphospholes Bearing 2‐ or 3‐Thienyl C‐Substituents

PS, I love you! Novel mixed phosphole/thiophene π‐conjugated systems were synthesized and their electronic properties have been studied both experimentally by UV/Vis spectroscopy and electrochemistry and by theoretical calculations. Exploiting the chemistry of both P‐ and S‐heteroles allows the generation of a diverse range of novel ring‐fused benzophosphole–thiophene derivatives.