Effects of substituents and charge on the RCHO⋯X–Y {X = Cl,Br, I; Y = –CF3, –CF2H, –CFH2, –CN, –CCH, –CCCN; R = –OH, –OCH3, –NH2, –O−} halogen-bonded complexes

Structural Chemistry - Noncovalent interactions involving halogen bonding interactions, one of the emerging interactions due to its directionality, have been a subject of interest for various...     

Intramolecular and intermolecular OH…O and OH…F interactions in perfluoropolyethers with polar end groups: IR spectroscopy and first-principles calculations

Perfluoropolyether (PFPE) fluids constitute a class of polymers that fulfil a wide range of requirements for hi-tech applications, due to their pefluorinated backbone. For some of these applications they are requested to bear polar end groups, and the combination of a chemical inert backbone and a reactive end group can produce peculiar conformations and supramolecular structures. The molecular structure and the vibrational properties of the ethoxyl-terminated PFPE FLUOROLINK®E10H in solution are here investigated by means of IR spectroscopy. It is shown that the complex spectral features of the OH-stretching region cannot be explained without a thorough computational study, involving the investigation of the conformational space of an isolated model molecule by means of semiempirical AM1 calculations and DFT calculations. The most relevant conformers were singled out, showing a high degree of conformational disorder for FLUOROLINK®E10H. Furthermore, it is shown that intra- and intermolecular H-bonding affects significantly the molecular structure and the vibrational spectrum. Several interactions are shown to be relevant, such as OH^…F interactions and complexes with residual water. Theoretical values of the absolute intensities of OH stretching IR bands, relevant for the analytical applications, are obtained.     

Effect of substituents (NH_2,OH,F) on structures and stability of lithofluorosilylenoids

Ｓｉｌｙｌｅｎｅｉｓｔｈｅｓｉｍｉｌａｒｉｔｙｏｆｓｉｌｉｃｏｎｔｏｃａｒｂｅｎｅ,ａｎｄ,ｌｉｋｅｃａｒｂｅｎｅｉｎｏｒｇａｎｉｃｒｅａｃｔｉｏｎｓ,ｉｔｐｌａｙｓａｖｅｒｙｉｍｐｏｒｔａｎｔｒｏｌｅｉｎｏｒｇａｎｏｓｉｌｉｃｏｎｒｅａｃｔｉｏｎｓ.Ｉｎｒｅｃｅｎｔｙｅａｒｓ,ｔｈｅｒｅｈａｖｅｂｅｅｎｍａｎｙｒｅｐｏｒｔｓｏｎｓｉｌｙｌｅｎｅｓｉｎｑｕａｎｔｕｍｃｈｅｍｉｃａｌｒｅｓｅａｒｃｈｅｓ[1—3].Ｉｎｖｅｓｔｉｇａｔｉｏｎｏｎｉｔｓｏｒｇａｎｉｃｒｅａｃｔｉｏｎｓｈｏｗｓｔｈａｔｒｅａｌｉ…     

λ-Shaped azomesogens with polar chloro- and nitro-substituents

A new homologous series of λ-shaped mesogenic azo esters with polar chloro- and nitro- substituents has been synthesised by attaching a rigid 2-chloro-4-nitrophenylazo group to a resorcinol moiety by a central azo linkage. Both phenolic hydroxyl groups are esterified by 4-n-alkoxybenzoyl groups. All the compounds synthesised have been characterised using a combination of elemental analysis and standard spectroscopic methods. The mesomorphic properties of the compounds have been determined by polarising optical microscopy and differential scanning calorimetry. The lower members of the series are non-mesogenic, the middle members exhibit a nematic mesophase, and higher members exhibit a smectic A mesophase. The effect of polar chloro-, nitro-, and long lateral aromatic substituents, on mesomorphism is discussed.     

Michael addition to 3-(2-nitrovinyl)indoles – route toward aliphatic nitro compounds with heterocyclic substituents

Chemistry of Heterocyclic Compounds - Synthetic approach toward indole derivatives bearing 2-nitroethyl group and polar azole moiety has been developed. This method involves conjugate addition of...     

Four-membered ring cyclic ketene –O,O–, –O,S–, –O,N–, –S,S–, –S,N–, and –N,N–acetals and their corresponding cations: a computational study

A systematic computational study of four-membered cyclic ketene –O,O–, –O,S–, –O,N–, –S,N– and –N,N-acetals as well as their protonated analogs have been performed at the second order M?ller Plesset level with a polarized triple zeta basis set. The main purpose of this study was to make predictions about the nucleophilicity of these systems and the variations in nucleophilicity with the hetero atoms. Our calculations suggest that all six target molecules are good nucleophiles, and that the N,N analog is the strongest and the S,S analog the weakest nucleophile. Our results include molecular geometries, bond lengths, proton affinities, vibrational frequencies, and calculated charges.     

Unsymmetrical 1λ3-1,2,4,6-thiatriazinyls with aryl and trifluoromethyl substituents: synthesis, crystal structures, EPR spectroscopy, and voltammetry

A general synthetic route to 3-trifluoromethyl-5-aryl-1λ(3)-1,2,4,6-thiatriazinyl radicals was developed. X-ray structures were obtained for all five neutral radicals and show that they exist in the solid state as cofacial dimers linked by S···S contacts. X-ray structures were also obtained for two of the precursor chlorothiatriazines along with several aryl N-imidoylamidines, p-methoxybenzamidine, and N-chlorosulfonyl-N,N'-benzamidine. Cyclic voltammetric studies were performed on the [R(2)C(2)N(3)S](?) radicals in CH(3)CN and CH(2)Cl(2) with [(n)Bu(4)N][PF(6)] as the supporting electrolyte under vacuum conditions in an all-glass electrochemical cell. The results provide quasi-reversible formal potentials for the [R(2)C(2)N(3)S](-/0) process in the range of -0.61 to -0.47 V, irreversible peak potentials for the [R(2)C(2)N(3)S](0/+) process from 0.59 to 0.91 V at lower concentrations, and the appearance of a second, reversible oxidation process from 0.69 to 0.94 V at higher concentrations (versus the Fc(0/+) couple; Fc = ferrocene). This behavior was indicative of monomer-dimer equilibrium in solution, as ascertained from digital models of the voltammograms. There is a small but measurable trend in both the oxidation and reduction potentials with varying remote aryl substituents. EPR spectra were obtained for all five neutral radicals in CH(2)Cl(2) solutions, which confirm the concentration of the unpaired electron density on the heterocyclic core. Trends were also seen in the hyperfine splitting constants a(N) with varying remote aryl substituents. Calculations were performed for all three oxidation states of the [R(2)C(2)N(3)S](-/?/+) monomeric rings; the resulting theoretical redox energies correlate well with solution phase voltammetric data.     

Frontier orbital interactions of electron pushing and drawing substituents with ferrocenyl group

The frontier orbital interactions of electron pushing and drawing substituents with ferrocenyl group were analyzed based on the electrochemical,UV visible spectral and spectroelectrochemical results of five ferrocene derivatives,R-Fc-A1(PⅠ),A1-Fc-A1(PⅡ),D-Fc-R (PⅢ),D-Kc-A1(PIV) and D-Fc-A2(PV)(R,CH2OH;A1 CHO;A2,CH=C(CN)2 and D,(C18H37)2N-C6H4-CH=CH) It was found that there are strong interactions of the LUMO (πA) of electron drawing substituents with le2g(dxy,dx2 y2)and e2u of the ferroeenyl group because the energy levels of πA and e2g,C2U of (Cp )2 are close,which lower not only the energy levels of bonded orbits,πA+ and dx2-y2+[πA] of PⅠ,PⅡ,PⅣ and PⅤobviously,but also those of their non-bonded orbu dxy For PⅢ,PⅣ and PⅤ,there are strong interactions of HOMO(πD) of the electron pushing substituent with le of the ferrocenyl group because the levels of πD and e of (Cp)2 are close,which result in the formation of anti-bonded orbit,πD- and bonded orbit     

Design of new organic superacids with fused and isolated pyrrole and cyclopentadiene rings and assessment of effect of –BX2 (X = H,F, Cl,CN) substituents on the acidity enhancement: A DFT analysis

New classes of organic Brønsted acids were designed with pyrrole and cyclopentadiene scaffolds, and their acidity was assessed theoretically by the B3LYP/6-311++G(d,p) method. The hydrogen atom of NH group in pyrrole was substituted by an –BX₂ (X = H, F, Cl, CN, CF₃). The boron atom stabilizes the conjugated bases by interaction with the center of negative charge after deprotonation. The acidity of the compounds was promoted by substitution of the hydrogen atoms of the rings with CN moiety as a strong electron withdrawing group. Also, after deprotonation, delocalization of the negative charge in both pyrrole and cyclopentadiene rings causes stability of the conjugated bases and consequently enhances the acidity. The charge delocalization in the neutral acids and their conjugated bases was compared using nucleus-independent chemical shift index. Enthalpies and Gibbs free energies of deprotonation in gas phase, ∆H_acid and ∆G_acid, were used as a measure of acidity. Both compounds with isolated and fused pyrrole and cyclopentadiene rings were investigated and it was found that the formers are more acidic. Using these strategies, several acids and superacids with wide range of acidity with ∆G_acid values of 244 to 328 kcal mol⁻¹ were obtained.     

Quantification of Noncovalent Interactions in Azide–Pnictogen, –Chalcogen,and –Halogen Contacts

The noncovalent interactions between azides and oxygen-containing moieties are investigated through a computational study based on experimental findings. The targeted synthesis of organic compounds with close intramolecular azide–oxygen contacts yielded six new representatives, for which X-ray structures were determined. Two of those compounds were investigated with respect to their potential conformations in the gas phase and a possible significantly shorter azide–oxygen contact. Furthermore, a set of 44 high-quality, gas-phase computational model systems with intermolecular azide–pnictogen (N, P, As, Sb), –chalcogen (O, S, Se, Te), and –halogen (F, Cl, Br, I) contacts are compiled and investigated through semiempirical quantum mechanical methods, density functional approximations, and wave function theory. A local energy decomposition (LED) analysis is applied to study the nature of the noncovalent interaction. The special role of electrostatic and London dispersion interactions is discussed in detail. London dispersion is identified as a dominant factor of the azide–donor interaction with mean London dispersion energy-interaction energy ratios of 1.3. Electrostatic contributions enhance the azide–donor coordination motif. The association energies range from −1.00 to −5.5 kcal mol⁻¹.     

Gas-phase solvation of Cl− with H2O,CH3OH,C2H5OH,i-C3H7OH,n-C3H7OH,and t-C4H9OH

The gas-phase clustering reactions Cl⁻ (ROH)n−1 + ROH ⇄ Cl⁻ (ROH)_n with n ⩽ 11 for ROH = H₂O, CH₃OH, C₂H₅OH, i-C₃H₇OH, n-C₃H₇OH, and t-C₄H₉OH were measured using a high-pressure mass spectrometer. It seems likely that for CH₃OH and C₂H₅OH, six ligands complete the shell structure and that ligands with n ⩾ 7 belong to the outer shell. The bond energies D(ROH---Cl⁻) increase in the order H₂O < CH₃OH < C₂H₅OH < i-C₃H₇OH < t-C₄H₉OH < n-C₃H₇OH. The observed strong bond of n-C₃H₇OH---Cl⁻ may be due to the fact that both the acidic hydrogen atoms in the −OH and terminal −CH₃ of n-C₃H₇OH interact with Cl⁻ with the most favorable configuration. For Cl⁻ switching reactions, Cl⁻ (H₂O)_n + (ROH)_n ⇄ Cl⁻ (ROH)_n + (H₂O)_n, the ΔG⁰_n values converge to the values of free energies of transfer of Cl⁻ from water to ROH solvent ( = ΔG⁰_n with n → ∞) with n ≈ 7. The observed convergence of ΔG⁰_n is due to compensation of changes in enthalpy and entropy, i.e. both ΔH⁰_n and TΔS⁰_n show increasing divergence from the values of enthalpies and entropies of transfer of Cl⁻ from water to ROH solvent, respectively, with n = 1 → 7. This is due to the stronger interactions of ROH with Cl⁻ than that of H₂O in the inner shell of Cl⁻ (ROH)_n at the expense of the less favorable entropy changes (less freedom of motion for ligands in the inner shell).     

Density functional study of substituted (–SH, –S, –OH, –Cl) hydrated ions of Hg<Superscript>2+</Superscript>

Abstract  

The electronic structure of Hg(II) ions, [Hg(L) _n (H₂O) _m ] ^q (L = HO⁻, Cl⁻, HS⁻, S²⁻) has been studied. Geometries were fully optimized. The B3LYP and PBE functionals give structures in good agreement with available experimental data. Calculated stretching frequencies generally correlate well with bond lengths. The role of the water molecule(s) in the solvated Hg(II) complexes has been investigated. The solvent can act as nucleophile, as hydrogen bond acceptor or as a spectator. The trans-effect results in lengthening of the Hg–L bond length. It can be understood as a competition between ligands in trans positions for the ability to donate their electron density to the 6s AO of Hg(II). The effect of the presence of water molecules on the Hg–L bond length depends on whether or not the water molecules form a direct coordination bond with Hg(II); it will not guarantee an increase in the stability of the complexes. The interaction energy, which represents the interaction between Hg(II) and ligand L and excludes all other interactions, is nucleophilicity-dependent. The interaction energy and the strength of the ligand nucleophilicity follow the order: S²⁻ > HS⁻ > HO⁻ > Cl⁻ > H₂O. The charge transfer, ΔN, is an indication for the type and strength of the interaction between ligand and Hg(II). Increasing the positive and negative value of ΔN will decrease and increase the Hg(II) total NBO charge, respectively, while decreasing the electrophilicity of Hg(II) will decrease its charge and the charge transfer, ΔN.     

Photoelectron spectra and electronic structure of boron difluoride β-diketonates with aromatic substituents

The electronic structure of boron difluoride chelate complexes of the acetyl acetonate type containing 4-biphenylene, 2-fluorene and 4-trans-stilbene as β-substituents is studied by means of photoelectron spectroscopy and quantum chemistry in the DFT approximation. It is established that the substituents affect the nature and sequence of the spectral bands. It is shown that calculation results corrected to the value of the Koopmans defect reproduce quite well the energy intervals between ionized states of complexes.     

Synthesis and characterization of α,ω-disubstituted quaterthiophenes functionalized with polar groups for solution processed OTFTs

A series of soluble quaterthiophenes (4Ta-g) bearing ester groups in the α,ω-terminal positions separated from the quaterthiophene core by ethylene (4Ta-c), vinylene (4Td-f) or ethynylene (4Tg) spacers was synthesized by means of a Pd-catalyzed homocoupling of bithiophenes proceeding via C-H bond activation. The synthetic approach gave satisfying yields of 4Ta-f but resulted in only 3% yield of 4Tg due to the competitive hydrofluorination of the triple bond. The quaterthiophenes 4Ta-g were characterized by NMR, FTIR, UV-vis, PL spectroscopies, HRMS, TGA and CV. Thin-films of 4Ta-g were deposited either by spin-coating or by thermal evaporation on Si/SiO₂ for the fabrication of top-contact OTFTs. The devices prepared using 4Ta-c bearing the ester functional group separated from the quaterthiophene core by an ethylene spacer showed average hole field-effect mobility up to 2.7×10⁻³ cm² V⁻¹ s⁻¹ and up to 6×10⁻³ cm² V⁻¹ s⁻¹ for solution processed and for thermally evaporated OTFTs, respectively. The remarkably high solubility of 4Ta-c, along with their respectable performances in OTFTs render these molecules promising for practical applications as active layers in chemically-sensitive devices.     

α,β-Dehydrogenation of esters with free OH and NH functionalities via allyl-palladium catalysis

A direct and selective method for the α,β-dehydrogenation of esters using palladium catalysis in the presence of free OH and NH functionalities is reported herein. Allyl-palladium catalysis allows for preservation of readily oxidizable functionalities such as amines and alcohols. Furthermore, an economical protocol using LDA was developed for the dehydrogenation of β-amino esters.     

Synthesis and anticancer activity of novel halolactones with β-aryl substituents from simple aromatic aldehydes

A series of 20 novel racemic iodo-, bromo- and chlorolactones, possessing β-phenyl-γ-lactone or β-phenyl-δ-lactone framework, were synthesized from commercially available aromatic aldehydes in convenient five-step syntheses. Some of them showed noticeable cytotoxic effect against two cancer lines, Jurkat (human leukaemia) and D17 (canine osteosarcoma). The highest activity, comparable with carboplatin, was observed for cis-5-(1-iodoethyl)-4-(4′-isopropylphenyl)dihydrofuran-2-one against Jurkat cell line.     

Synthesis of (η-arene)(η-cyclopentadienyl) iron (II) complexes with heteroatom and carbonyl substituents. Part I: Oxygen and carbonyl substituents

A series of reactions have been used to introduce oxygen substituents into (η-arene)(η-cyclopentadienyl) iron (II) complexes. Photochemical ligand exchange led to the formation of the first recorded trioxygenated complex as well as mono- and di-oxygenated species. Using microwave techniques, reaction times for S_NAr displacement reactions of halobenzene complexes by phenols were reduced from several hours to a few minutes. Phenols protected by either t-butylation or trimethylsilylation were found to give modest yields of the corresponding phenol complexes, using conventional thermal ligand exchange reactions. Without such protection, yields were extremely low. The above method led to the synthesis of the first example of a dihydroxybenzene complex. Some miscellaneous syntheses are also reported.The Nef reaction has been adapted to convert (η⁶-α-nitroalkylarene)(η⁵-Cp) iron (II) salts to corresponding aldehyde and ketone complexes. The α-nitroalkyl arene complexes were synthesised in good yields from (η⁶-halobenzene)(η⁵-Cp) iron (II) complexes using NaOtBu in DMSO. H/D exchange reactions with ²[H]₆-DMSO in the presence of K₂CO₃ showed partial D incorporation in the methyl group for the unreacted α-nitroethylbenzene complex and complete exchange for the carbanion generated by deprotonation. Conversion of the α-nitroalkylarene complexes to the corresponding aldehyde and ketone complexes was accomplished in moderate yields using three methods:

(A)

H₂O₂ and NaOtBu in DMSO followed by reaction with CF₃CO₂H.

(B)

SnCl₂/aq. HCl.

(C)

K₂CO₃ in DMF using microwave-mediated reactions.

In addition, two one-pot syntheses are reported using methods B and C.     

Investigation of the sorption properties of β-cyclodextrin-based polyurethanes with phenolic dyes and naphthenates

The sorption of p-nitrophenol (PNP), phenolphthalein (phth) and naphthenates (NAs) with β-cyclodextrin (β-CD) based polyurethane sorbents from aqueous solutions are reported. The copolymer sorbents were synthesized at various β-CD/diisocyanate monomer mole ratios (e.g., 1:1, 1:2, and 1:3) with diisocyanates of variable molecular size and hydrogen deficiency. The copolymer sorbents were characterized in the solid state using (13)C CP-MAS NMR spectroscopy, IR spectroscopy and elemental (C,H,N) analysis. The equilibrium sorption properties of the copolymer sorbents in aqueous solution were characterized using isotherm models at pH 4.6 and 9.0 for PNP, pH 9.0 for naphthenates and pH 10.5 for phth. UV-Vis spectroscopy was used to monitor the unbound fraction of the phenolic dyes in the aqueous phase, whereas, electrospray ionization mass spectrometry was used to monitor the unbound fraction of naphthenates. The sorption results of the copolymer sorbents were compared with a commercially available carbonaceous standard; granular activated carbon (GAC). The sorption properties and capacities of the copolymer sorbents (Q(m)) were estimated using the Sips isotherm. The sorption capacity for GAC was 2.15 mmol PNP/g, 0.0698 mmol phth/g, and 142 mg NAs/g, respectively, whereas the polymeric materials ranged from 0.471 to 1.60 mmol/g (PNP), 0.114 to 0.937 mmol/g (phth), and 0 to 75.5 mg/g (naphthenates), respectively, for the experimental conditions investigated. The observed differences in the sorption properties were attributed to the accessible surface areas and pore structure characteristics of the copolymer sorbents. The binding constant, K(eq), for copolymer materials for each sorbate is of similar magnitude to the binding affinity observed for native β-CD. PNP showed significant binding onto the copolymer framework containing diisocyanate domains, whereas, negligible sorption to the sites was observed for phth and naphthenates. The β-CD inclusion sites in the copolymer framework are concluded to be the main sorption site for phth and naphthenates through the formation of well-defined inclusion complexes.     

Aromaticity of benzenoid hydrocarbons with inserted –B=B– and –BH–BH– groups: a comparison

Structures of selected polycyclic conjugated hydrocarbons with –B=B– and –BH–BH– moieties inserted in different places were calculated at the B3LYP/6-311++G** level and their aromatic properties evaluated. HOMA, NICS(0), NICS(1)zz, Λ and PDI indices were used for studying their aromatic properties. Both optimized planar (as in parent hydrocarbons) and non-planar structures were taken into account. It is shown that insertion of both types of boron groups disturbs and decreases the aromaticity of the corresponding hydrocarbons. The decreasing effect of the –BH–BH– group is much stronger. What is quite intriguing is that it appears that non-planar structures of the studied compounds have a little higher aromaticity than the strictly planar ones. Mutual correlations between results obtained by different aromaticity indices are calculated and thoroughly discussed.