Weak hydrogen-, halogen- and stacking ππ bonding in crystalline 5-chloro-1-indanone. An analysis by using X-ray diffraction, vibrational spectroscopy and theoretical methods

Intermolecular forces of C–HO, C–Hπ, COCl and ππ types are present in the stable triclinic crystal structure of 5-chloro-1-indanone. They are analysed from a geometrical point of view supported in some extent by the analysis of the vibrational spectrum of the titled compound. Moreover, the molecular structure of the isolated species is calculated by using ab initio as well as density functional theory (DFT) methods together an assortment of basis sets. In order to obtain some information about the influence of intermolecular forces on the molecular structure, the calculated geometries of a free molecule were compared with the experimental solid phase geometry determined by X-ray crystallography.An analysis and assignment of the vibrational spectrum of the 5-chloro-1-indanone is accomplished by using IR and Raman experimental data along with Pulay et al.’s scaled quantum mechanical force field (SQM) methodology starting from the theoretical B3LYP/6-31G(d) and BLYP/6-31G(d) force fields under C_s symmetry.     

The catalytic effects of various third molecules on reaction channels of weakly bound complex CO2HF systems in the vapor phase

In this investigation, reaction channels of weakly bound complexes CO₂HF, CO₂HFH₂O, CO₂HFNH₃, CO₂HFCH₃OH, CO₂HFNH₂CH₃, CO₂HFNH(CH₃)₂ and CO₂HFN(CH₃)₃ systems were studied at the B3LYP/6-311++G(3df,2pd) level. The conformers of syn-fluoroformic acid or syn-fluoroformic acid plus a third molecule (H₂O, NH₃, CH₃OH, NH₂CH₃, NH(CH₃)₂ or N(CH₃)₃) were found to be more stable than the conformers of the related anti-fluoroformic acid or anti-fluoroformic acid plus a third molecule (H₂O, NH₃, CH₃OH, NH₂CH₃, NH(CH₃)₂ or N(CH₃)₃). However, the weakly bound complexes were found to be more stable than either the related syn- and anti- type fluoroformic acid or the acid plus third molecule (H₂O, NH₃, CH₃OH, NH₂CH₃, NH(CH₃)₂ or N(CH₃)₃) conformers. They decomposed into CO₂+HF, CO₂+H₃OF, CO₂+NH₄F, CO₂+(CH₃)OH₂F, CO₂+NH₃(CH₃)F, CO₂+NH₂(CH₃)₂F, or CO₂+NH(CH₃)₃F combined molecular systems. The weakly bound complexes have seven reaction channels, each of which includes weakly bound complexes and their related systems. Moreover, each reaction channel includes two transition state structures. The transition state between the weakly bound complex and anti-fluoroformic acid type structure (T₁₃) is significantly higher than that of internal rotation (T₂₃) between the syn- and anti-FCO₂H (or FCO₂HH₂O, FCO₂HNH₃, FCO₂HCH₃OH, FCO₂HNH₂CH₃, FCO₂HNH(CH₃)₂, or FCO₂HN(CH₃)₃) structures. However, adding the third molecule H₂O, NH₃, CH₃OH, NH₂CH₃, NH(CH₃)₂ or N(CH₃)₃ can significantly reduce the activation energy of T₁₃. The catalytic strengths of the third molecules are predicted to follow the order H₂O<NH₃<CH₃OH<.NH₂CH₃<NH(CH₃)₂<N(CH₃)₃.     

A theoretical study on NH bond dissociation enthalpies of oxo, thio and seleno carbamates and their N-protonated and N-deprotonated species

The effect of N-protonation and N-deprotonation on structure, NH bond dissociation enthalpies (BDEs) and stabilities of radicals formed on H-abstraction from nitrogen atom of carbamates and their thio- and seleno-analogs have been investigated. For those molecules where experimental results are available for comparison, the ROB3LYP/6-311++G(d,p)//B3LYP/6-31+G* theoretical level is in agreement within the estimated experimental uncertainty. The NH BDE of carbamates H₂NC(=X)YCH₃ [X = O; Y = O, S, Se] are higher but lower when X = S, Se and Y = O, S, Se in comparison to NH BDE of NH₃. DFT calculations indicate that the NH bond dissociation enthalpies are decreased by protonation and deprotonation at nitrogen atom; but the effect of deprotonation is rather smaller than the protonation. The variations are analyzed in terms of stabilities of molecules, their protonated and deprotonated species along with their respective radicals. The electron delocalization from nitrogen, X and Y atoms, electrostatic interactions, conjugative interactions and spin delocalization are the important factors affecting the stability. The spin delocalization and shift of radical center to chalcogen X (X = S, Se) are the main determinants for radical stability.     

Quantum mechanical studies of the protonation and NBr bond dissociation of the biologically important N-bromosuccinimide

N-Bromosuccinimide (NBS) is a brominating and oxidizing agent that is used as a source of bromine. The proton affinities, the tautomeric forms and NBr bond dissociation of NBS have been computed using the B3LYP functional as implemented in the density functional approach. The electronic structures of all possible tautomeric forms of NBS have been thoroughly investigated. The keto form of NBS has been shown to be more stable than any other tautomeric forms. The geometries and relative energies for various stationary structures were determined. The results indicate clearly that O-site protonation is strongly favored over N-site protonation for the studied compound in case of mono- and di-protonation. The bond dissociation energies (BDEs), involving the formation of the bromine radical, cation, and anion, of the NBr bond have been investigated. The NBr BDE of the Br radical formation is lower than that of the Br anion or cation. These conclusions are in good agreement with the experimental results.     

Reaction of diacetylmonoxime with morpholine N-thiohydrazide in the absence and in presence of a metal ion: Facile synthesis of a thiadiazole derivative with non-bonded SS interaction

The condensation of diacetylmonoxime (damnx) with morpholine N-thiohydrazide (mth) in 1:1 molar ratio in ethanol (16 h) afforded a nitrogen–sulfur zwitterionic heterocyclic compound, N-(3,4-dimethyl-1,2,5-thiadiazole-2-ium-2-yl)morpholine-4-carbothioate (dtmc). However, the same reaction in presence of [Zn(OAc)₂]·2H₂O in ethanol under gentle reflux on (3 h) yielded the zinc complex, [Zn(Hdammthiol)(OAc)(H₂O)]·H₂O, where H₂dammthiol (H₂L²) is the thiol form of tridentate NNS donor thiohydrazone ligand, diacetylmonoxime morpholine N-thiohydrazone (Hdammth). Both the nitrogen–sulfur heterocyclic compound and the zinc complex have been characterized by elemental analyses, spectroscopy (IR, UV–Vis, ¹H NMR and ¹³C NMR) and single crystal X-ray crystallography. It is noteworthy that the heterocyclic compound shows SS interaction with distance 2.738 Å in its planar conformation. The heterocyclic compound forms two dimensional supramolecular sheets through C–HO and ππ interactions while the zinc complex, with distorted square pyramidal geometry, forms 1D supramolecular chain. A mechanism has been proposed for the formation of nitrogen–sulfur heterocyclic compound.     

Homogeneous and supported copper(II) acetate as catalyst for CO coupling reactions

The reactivity of copper(II) acetate as catalyst in a standard CO coupling reaction has been systematically evaluated. Optimization of the reaction conditions resulted in a protocol involving stoichiometric amounts of reagents, a substoichiometric amount of base and 20 mol% catalyst, at 50 °C in 1,2-dichloroethane and under 1 atm O₂. Next, the reactivity of polymer-supported copper(II) acetate was evaluated. Although it is found that, in contrast to previous results obtained in related CN coupling reactions, the polymer-supported catalyst is in this case less efficient than the corresponding homogeneous one, the catalyst turns out to be conveniently recovered from the reaction mixture by simple filtration.     

Nonadiabatic dissociation dynamics of ClHD van der Waals complex initiated by electron detachment of Cl–HD

Nuclear dynamics following the electron detachment of the Cl⁻–HD anion is investigated by a time-dependent wave packet propagation approach. Photodetachment of Cl⁻–HD promotes it to the van der Waals well region of the reactive ClHD potential energy surface. The latter is a manifold of three electronic states coupled by the electronic and (relativistic) spin-orbit coupling. Among the three surfaces, the electronic ground one is of ²Σ_1/2 type and yields products in their electronic ground state. The remaining two, ²Π_3/2 and ²Π_1/2, on the other hand, yield products in their excited electronic states. However, these two can yield products in their electronic ground state via nonadiabatic transitions to the ²Σ_1/2 state. The channel specific, HCl + D or DCl + H or Cl + HD, dissociation probabilities on this latter state are calculated both in the uncoupled and coupled surface situations. Separate initial transitions (via, photodetachment) to the ²Σ_1/2, ²Π_3/2 and ²Π_1/2 adiabatic electronic states of ClHD are considered in order to elucidate the nonadiabatic coupling effects on this important class of chemical reactions initiated by an electron detachment.     

H NMR Dynamic study of thermal Z/E isomerization of 5-substituted 2-alkylidene-4-oxothiazolidine derivatives: Barriers to rotation about CC bond

The rotational barriers between the configurational isomers of two structurally related push–pull 4-oxothiazolidines, differing in the number of exocyclic CC bonds, have been determined by dynamic ¹H NMR spectroscopy. The equilibrium mixture of (5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone (1a) in CDCl₃ at room temperature to 333 K consists of the E- and Z-isomers which are separated by an energy barrier ΔG^# 98.5 kJ/mol (at 298 K). The variable-temperature ¹H NMR data for the isomerization of ethyl (5-ethoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)ethanoate (2b) in DMSO-d₆, possessing the two exocyclic CC bonds at the C(2)- and C(5)-positions, indicate that the rotational barrier ΔG^# separating the (2E,5Z)-2b and (2Z,5Z)-2b isomers is 100.2 kJ/mol (at 298 K). In a polar solvent-dependent equilibrium the major (2Z,5Z)-form (>90%) is stabilized by the intermolecular resonance-assisted hydrogen bonding and strong 1,5-type S · · · O interactions within the SCCCO entity. The ¹³C NMR Δδ_C(2)C(2′) values, ranging from 58 to 69 ppm in 1a–d and 49-58 ppm in 2a–d, correlate with the degree of the push-pull character of the exocyclic C(2)C(2′) bond, which increases with the electron withdrawing ability of the substituents at the vinylic C(2′) position in the following order: COPh COEt > CONHPh > CONHCH₂CH₂Ph. The decrease of the Δδ_C(2)C(2′) values in 2a–d has been discussed for the first time in terms of an estimation of the electron donor capacity of the S fragment on the polarization of the CC bonds.     

Theoretical investigation of C–HM interactions in organometallic complexes: A natural bond orbital (NBO) study

The nature of C–HM agostic interactions in model metal complexes [M²⁺(CH₂CH₃)(PH₃)_nCl] (where M = Sc, Ti, V, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn; n = 1, 2, 3, 4) was studied with the natural bond orbital analysis (NBO) approach using density functional theory (DFT) optimized geometries at the B3LYP/6-31G(d,p) level of theory. The effect of nature of metal, coordination number, oxidation state and ligand field effects on the agostic interaction is examined. A set of 20 crystal structures of organometallic complexes taken from the Cambridge Structural Database (CSD) was studied computationally employing AIM theory and NBO analysis, and the applicability of these methods was critically accessed in demarcating the two types of interaction.     

Theoretical study of the influence of para- and meta-substituents on X-pyridineHF hydrogen bonding

The effects of O⁻, N (CH₃)₂, NH (CH₃), NH₂, C₂H₅, CH₃, OH, F, Cl, OF, Br, NO₂ and substituents in para- and meta-positions on X-pyridineHF hydrogen bond has been studied by HF, B3LYP and MP2 methods using 6-311++G(d,p) basis set. The relationship between hydrogen bond formation energy ΔE and electron donating (or withdrawing) of substituents has been investigated. In this respect, population analysis has been performed by atoms in molecules (AIM) and natural bond orbital (NBO) theories. The results of AIM and NBO analyses are in good agreement with calculated energy values. The relationship between Hammett coefficient and complexation energy has been established and the ρ constant has been calculated for hydrogen bonding. There is a relationship between σ and ΔE with a correlation coefficient equal to 0.94.     

C–HPt(II) interaction-controlled self-assembly and photophysics of chiral bis(pyrrol-2-ylmethyleneamino)cyclohexane platinum(II) complexes

Reaction of (R,R)-(−)- and (S,S)-(+)-1,2-bis(pyrrol-2-ylmethyleneamino)cyclohexane with K₂PtCl₄ afforded chiral, neutral platinum(II) Schiff base complexes of (R,R)-PtL and (S,S)-PtL with high yields. The rare C–HPt(II) intermolecular interaction was found to show considerable strength and directionality for controlling M and P helical supramolecular architectures of (R,R)-PtL and (S,S)-PtL, respectively, in crystal lattices. More importantly, the open square-planar geometry of platinum(II) complexes allows axial C–HPt(II) interaction, resulting in the ³(ππ^*) excited state with some mixing of the Pt(II) metal character observed both in concentrated solutions and in the solid state at room temperature.     

Effects of dipole interaction and solvation on the CO stretching band of N,N-dimethylacetamide in nonpolar solutions: Infrared, isotropic and anisotropic Raman measurements

The concentration dependence of the CO stretching (ν_CO) band of N,N-dimethylacetamide (NdMA) in cyclohexane, n-hexane, and CCl₄ has been investigated by infrared (IR) and polarized Raman spectroscopy. For the neat liquid of NdMA, the noncoincidence of the aniso- and isotropic Raman wavenumbers is evident. In the 0.47 M cyclohexane solution of NdMA, the noncoincidence effect almost disappears and the ν_CO envelopes in both the Raman and IR spectra are asymmetric to the low-wavenumber side. When the concentration of NdMA decreases from 0.33 to 0.023 M, the peak of these bands slightly shifts to a higher wavenumber and the band shape becomes symmetric. The shape of the ν_CO envelope does not show any significant change below 0.023 M. These results suggest that the asymmetric shape of the ν_CO band observed for the 0.33 M cyclohexane solution is associated with the intermolecular interaction among NdMA molecules, which vanishes at around 0.02 M. Spectral changes for the CCl₄ solution of NdMA show a similar tendency. However, the shape and peak wavenumber of the ν_CO band observed in a highly diluted CCl₄ solution (≤0.023 M) indicate that the solvation effect of CCl₄ is more complicated than those of cyclohexane and n-hexane. The analyses of the ν_CO band, which is sensitive to the intermolecular interaction between solutes and between solute and solvent for NdMA dissolved in nonpolar solvents, would serve to clarify the electronic property of the molecule in a solution.     

Atmospheric chemistry of CF3CFCH2: Products and mechanisms of Cl atom and OH radical initiated oxidation

The products of Cl atom and OH radical initiated oxidation of CF₃CFCH₂ were studied in 700 Torr of N₂/O₂ diluent at 296 ± 1 K. The reactions of Cl atoms and OH radicals with CF₃CFCH₂ proceed via electrophilic addition to the double bond. The reaction with chlorine atoms proceeds 56 ± 5% via addition to the central carbon. The chlorine atom initiated oxidation of CF₃CFCH₂ gives CF₃C(O)F in a molar yield which is indistinguishable from 100% and independent of [O₂], and HC(O)Cl in a molar yield which increased from 30% to 59% as [O₂] was increased from 3 to 700 Torr. The OH radical initiated oxidation of CF₃CFCH₂ gives CF₃C(O)F as major product in a yield of 91 ± 6%. The results are discussed with respect to the atmospheric chemistry and environmental impact of CF₃CFCH₂.     

Bonding trends in MCH2 systems: Simple orbital interpretation and evidence for double bonds

MCH₂ systems, where M is a metal from 4th up to 7th period, are studied at DFT level using B3LYP functional and small-core quasirelativistic pseudopotential or fully relativistic four-component methodology. We obtained structural data for 44 elements, M, and our results can be used to infer double-bond lengths for these elements. Our results also suggest that the bonding of these MCH₂ systems can be understood by a simple pictorial approach, even when spin–orbit effects are present.     

Interligand interactions involved in the molecular recognition between copper(II) complexes and adenine or related purines

The available crystal structure information in the CSD database on ternary species prepared by the reaction of diverse copper(II) complexes (CuL) and purine, adenine and guanine or related purine derivatives is considered in order to deepen the intra-molecular interligand interactions affecting the molecular recognition patterns of the ‘metal complex + purine nucleobase’ and closely related systems. The degree of protonation and the possibilities of different tautomeric forms in the purine-like moieties are taken into account. The main conclusion is a general trend to form a CuN(purine-like) coordination bond which can be reinforced by an intra-molecular interligand H-bonding interaction. NH(purines)A (O or Cl acceptor) or NH(amino ligand L)O6(oxo-purines) are commonly observed. In addition, selected examples revealed that the presence of a variety of non-coordinating groups in L or in the purine-like nucleobases can significantly influence the structurally observed molecular recognition pattern. Moreover, examples are known where binuclear cores of the types Cu^II₂(μ₂-N3,N9-adeninate)₄(aqua)₂ or Cu^I₂(μ₂-N3,N9-adeninate)₂(aqua)₂ recognise CuL chelates by means of the expectable pattern (CuN7 coordination bond + N6HO(L) interaction).     

Novel BrФnsted Acidic Ionic Liquid Based on a Cyclic Guanidinium Cation： a Green, Efficient, and Recyclable Dual Slovent-catalyst System for Fisher Esterification

A novel Brфnsted acidic ionic liquid(IL)based on the cyclic guanidinium cation has been synthesized.This IL,as a strong Brфnsted acid catalyst or solvent,shows high catalytic activity and biphsaic behavor in the esterifications of carboxylic acids and alcohols.The produced esters as a separate phase can be conveniently decanted out from the IL and the IL is recyclable without any loss of catalytic activity.     

Phase controllable synthesis of unusual -Ga2O3 single crystals with promising luminescence property

A new synthetic approach to unusual -Ga₂O₃ with improved luminescence properties was developed by taking advantage of a microwave-assisted synthesis followed by calcinations at appropriate temperatures. Upon control of crystallinities of GaOOH precursors and the followed calcination temperature, the single crystalline -Ga₂O₃ nanorods can be synthesized in a large scale. The resulting products were characterized by transmission electron microscopy, powder X-ray diffraction, and cathodoluminescence. The luminescence property of this unusual Ga₂O₃ phase was investigated for the first time.     

The structure of p-chlorophenol and barrier to internal OH rotation in the S1-state

The structure and barrier to internal rotation of 4-chlorophenol in the ground state and the electronically excited S₁-state has been examined by rotationally resolved laser induced fluorescence spectroscopy of 4-³⁵Cl-phenol, 4-³⁷Cl-phenol, 4-³⁵Cl-phenol-d₁, and 4-³⁷Cl-phenol-d₁. The overlapping spectra have been assigned simultaneously using a genetic algorithm approach. The rotationally resolved spectrum of the electronic origin of 4-chlorophenol is comprised of two subbands, which are split by 60 MHz due to the internal rotation of the hydroxy group. The torsional barrier in the electronically excited state could be estimated to be 1400 cm⁻¹, only about 250 cm⁻¹ higher than in the ground state. The CCl bond lengths decreases by approximately 6 pm upon electronic excitation and the aromatic ring is distorted quinoidally.     

Hydrogen-bond structures in poly(2-hydroxyethyl methacrylate): Infrared spectroscopy and quantum chemical calculations with model compounds

Hydrogen-bond structures in poly(2-hydroxyethyl methacrylate) (PHEMA) were investigated by infrared (IR) spectroscopy and quantum chemical calculations (QCC). A monomer of 2-hydroxyethyl methacrylate (HEMA) and model compounds of methyl acetate (MA) and methanol (MeOH) were also used. Evidences for OHOC and OHOH types of hydrogen-bonds were observed in an IR spectrum of a PHEMA solid. It was estimated from the present study that 47.3% of OH groups on the PHEMA side chain terminal are engaged in the OHOC type of hydrogen-bond, while the rest contributes to the OHOH type of hydrogen-bond.     

Unimolecular chemistry of metastable dimethyl isophthalate radical cations

The MS/MS spectrum of the metastable molecular ions of dimethyl isophthalate 1 differs from that of the isomeric dimethyl terephthalate 2 by the observation of, inter alia, a quite intense loss of C,H₂,O ascribed to formaldehyde. Results obtained using a combination of mass spectrometry techniques suggest that this process could consist of an isomerization reaction of the molecular ion into an ion–neutral complex (INC) linking a benzoyl radical and neutral formaldehyde to a proton [ArCOHOCH₂]⁺. Within the complex, a proton transfer catalyzed by formaldehyde occurs resulting in the production of an ionized cyclohexadienylidene methanone (ketene) structure.