Halide Molecules Research Articles

Carbide-derived carbon obtained via bromination of titanium carbide: Comparative analysis with chlorination and hydrogen storage studies

Carbide-derived carbons (CDCs) are synthesized from TiC micropowder via gas phase bromination at the temperature range of 350–1150 °C. The resultant carbon materials demonstrate high specific surface areas and micropore volumes of up to 1745 m2 g−1 and 0.64 cm3 g−1 respectively. Successful bromination of TiC in a wide temperature range permitted the first in-depth comparative study of CDCs produced by Br2 and Cl2 thermochemical extraction. Although minor, some structural differences between TiC-CDCs obtained via bromination and chlorination reactions are observed. It is concluded that it is not the size of halogen and evolving titanium halide molecules but the reactivity of the halogen that affects the microporosity of TiC-CDCs. The structural similarity of materials obtained via Br2 and Cl2 extraction proves that the extractive step does not determine the final structure of CDCs. Cryogenic high-pressure hydrogen storage studies show that the maximum excess hydrogen uptake of TiC-CDCs strongly correlates to the volume of micropores below 1.75 nm in size.

A strategic review on processing routes towards highly efficient perovskite solar cells

An organic–inorganic perovskite is comprised of an organic cation (CH3NH3+, FAI, or Cs), a metal cation (Pb2+or Sn2+) and a halide (I−, Cl−, or Br−) molecule.

Infrared Spectroscopic and Electronic Structure Investigations of Beryllium Halide Molecules, Cations, and Anions in Noble Gas Matrices.

Laser-ablated Be atoms, cations, and electrons were reacted with F2, ClF, Cl2, NF3, CCl4, CF2Cl2, HCl, DCl, and SiCl4 diluted in noble gases. The major products were the dihalides BeF2, BeClF, BeCl2, and the hydride chloride HBeCl, whose identities were confirmed by comparison with previous evaporative work, deuterium substitution, and vibrational frequency calculations. The matrix-isolated fundamental frequency of the BeF molecule is higher, and the frequency of BeCl is lower, than that determined for the gas-phase molecules. The BeF+ and BeCl+ cations formed strong dipole-induced dipole complexes in solid Ne, Ar, Kr, and Xe with stepwise increase in computed noble gas dissociation energies. Going down the family NgBeF+ and NgBeCl+ series (Ng = Ne, Ar, Kr, Xe) the Mulliken charges q(Be) decrease, while q(Ng) increases, and the dipole moments decrease, which suggests covalent bonding in the xenon species. We find that the largest intramatrix shift is Ne to Ar which follows the largest factor increase for the Ng atomic polarizabilities. Extra electrons produce Cl-, which reacts with HCl to form the stable HCl2- anion and possibly with BeCl2 to give BeCl3-. A weak band observed in neon experiments with F2 is probably due to BeF3-.

Halogen-Bond-Based Molecular Self-Assembly on Graphene Surface: A First-Principles Study

The formation of halogen-bond-based 2D supramolecular assemblies on solid surfaces has become a hot research topic in recent years. Herein, we report a theoretical study of the halogen-bonded network formation of pyridine derivatives and aryl–halide molecules on graphene surface using first-principles density functional theory (DFT) calculations. To unravel the characteristics of molecule–molecule and molecule–substrate interactions, the noncovalent interaction index (NCI), electron density difference (EDD), density of state (DOS), and topographical scan tunneling microscopy (STM) image analyses were undertaken. The N···I interactions between terminal pyridyl groups and iodoperfluorobenzenes are predicted to be somewhat stronger than the molecule–surface stacking interactions and appear to be the primary interactions in the self-assembled networks, with geometries in good agreement with the experimental STM images. The results reported in this work should be of great importance in the applications of thes...

Electrophilic addition/substitution of an alkynyl methyl ketone with tellurium tetrahalides: A novel synthetic approach to telluracyclopentenones

The interaction of tellurium tetrahalides, TeX4 (X = Cl. Br) with 4-(trimethylsilyl)but-3-yn-2-one under dry nitrogen gives novel crystalline 1,1,3-trihalo-2-(trimethylsilyl)telluracyclopent-2-en-4-ones (X = Cl, 1a and X = Br, 2b) as the major products. In a tandem reaction, the trisubstituted vinyltellurium trihalide formed initially by the anti addition of a tellurium tetrahalide across the polar triple bond of the 1,2-disubstituted acetylene, instantly undergoes intramolecular electrophilic substitution of the carbonyl activated methyl protons to eliminate a molecule of hydrogen halide. These tellurium(IV) derivatives can be reduced safely with aqueous sodium meta bisulphite to give tellurium(II) heterocyles, 3-halo-2-(trimethylsilyl)telluracyclopent-2-en-4-ones as fairly stable viscous oils. Molecular geometry of 1a as substantiated from the single-crystal X-ray diffraction data has Cs symmetry and resembles a see-saw with a pentagonal stand that supports the Cl─Te─Cl beam at the Te atom as its fulcrum.

Palladium-Catalyzed, tert-Butyllithium-Mediated Dimerization of Aryl Halides and Its Application in the Atropselective Total Synthesis of Mastigophorene A.

A palladium-catalyzed direct synthesis of symmetric biaryl compounds from aryl halides in the presence of tBuLi is described. In situ lithium-halogen exchange generates the corresponding aryl lithium reagent, which undergoes a homocoupling reaction with a second molecule of the aryl halide in the presence of the palladium catalyst (1 mol %). The reaction takes place at room temperature, is fast (1 h), and affords the corresponding biaryl compounds in good to excellent yields. The application of the method is demonstrated in an efficient asymmetric total synthesis of mastigophorene A. The chiral biaryl axis is constructed with an atropselectivity of 9:1 owing to catalyst-induced remote point-to-axial chirality transfer.

Palladium‐Catalyzed, tert‐Butyllithium‐Mediated Dimerization of Aryl Halides and Its Application in the Atropselective Total Synthesis of Mastigophorene A

AbstractA palladium‐catalyzed direct synthesis of symmetric biaryl compounds from aryl halides in the presence of tBuLi is described. In situ lithium–halogen exchange generates the corresponding aryl lithium reagent, which undergoes a homocoupling reaction with a second molecule of the aryl halide in the presence of the palladium catalyst (1 mol %). The reaction takes place at room temperature, is fast (1 h), and affords the corresponding biaryl compounds in good to excellent yields. The application of the method is demonstrated in an efficient asymmetric total synthesis of mastigophorene A. The chiral biaryl axis is constructed with an atropselectivity of 9:1 owing to catalyst‐induced remote point‐to‐axial chirality transfer.

Effect of vibronic interactions on molecular structures determined by gas electron diffraction

This paper reviews advances of modern gas electron diffraction (GED) method combined with high-resolution spectroscopy and quantum-chemical calculations in studies of the impact of vibronic interactions in free molecules on their structures and nuclear dynamics. Some recently developed approaches to the electron diffraction data interpretation, based on direct incorporation of the adiabatic potential energy surface (APES) parameters to the diffraction intensity, are described. It is suggested that by using the proposed approaches, it is possible to develop a common “language” with spectroscopy and computation methods. In this way, complementary data of different experimental and computational methods can be directly combined for solving problems of the molecular structure and its dynamics. The possibility to evaluate some important parameters of the APES–vibronic interaction constants from electron diffraction intensities in solving the inverse GED problem is demonstrated on several examples. This approach makes it possible to get the proper symmetry of the molecule and the Euclidian relations between internuclear distances in the framework of the APES. With increasing accuracy of the electron diffraction intensities and the development of the theoretical background of electron scattering and data interpretation, it has become possible to investigate complex nuclear dynamics in vibronic systems by the GED method. Magdolna Hargittai and her associates have demonstrated the presence and importance of the Jahn–Teller, Renner–Teller, and pseudo-Jahn–Teller effects in gaseous metal halide molecules, and they are quoted in this paper. Results of other research groups are also included in the discussion.

Adsorption of acetyl halide molecules on the surface of pristine and Al-doped graphene: Ab initio study

We have scrutinized the adsorption energy, electronic structure, natural bond analysis (NBO), density of state (DOS) and global indices for adsorption of acetyl chloride (AC) and acetyl fluoride (AF) on the surface of pristine graphene as well as Al-doped graphene. The adsorption energies have been calculated for the most stable configurations of the molecules on the surface of pristine and Al-doped graphene. According to the calculated parameters, there is very weak physical adsorption of AC and AF on pristine graphene while strong adsorption takes place in the case of Al-doped graphene. The charge transfer from adsorbed molecules to Al-doped graphene surface was confirmed by the natural bond orbital as well as the Mulliken population analysis while there is no charge transfer with pristine graphene. Additionally, the density of states results reveal that orbital hybridization takes place between above-mentioned molecules and Al-doped graphene sheet, whereas there is no hybridization between the molecules and the pristine graphene. Our calculated adsorption energies for the most stable position configurations of AC and AF on Al-doped graphene were −68.8kJmol−1 (−52.6kJmol−1 BSSE corrected energy) and −78.4kJmol−1 (−64.3kJmol−1 BSSE corrected energy) which are correspond to chemisorptions process respectively. These results point to the appropriateness of Al-doped graphene as a powerful adsorbent for practical applications.

Computational studies of boron- and nitrogen-doped single-walled carbon nanotubes as potential sensor materials of hydrogen halide molecules HX (X = F, Cl, Br)

Potential applicability of undoped, B-, and N-doped carbon nanotubes (CNTs) for elaboration of the working materials of gas sensors of hydrogen halide molecules HX (X = F, Cl, Br) is analyzed in computational studies of molecular adsorption on the CNTs surfaces. Density Functional Theory (DFT)-based geometry-optimized calculations of the electronic structure of undoped, B-, and N-doped CNTs of (3,3) and (5,5) chiralities with adsorbed HX (X = F, Cl, Br) molecules are performed within molecular cluster approach. Relaxed geometries, binding energies between the adsorbates and the nanotubes, charge states of the adsorbates and the electronic wave function contours are calculated and analyzed in the context of gas sensing applications. Obtained results are supplemented by calculations of adsorption of hydrogen halides on B(N)-doped graphene sheets which are considered as model approximation for large-diameter CNTs. It is found that the B-doped CNTs are perspective for elaboration of sensing materials for detection of HCl and HBr molecules. The undoped and the N-doped CNTs are predicted to be less suitable materials for detection of hydrogen halide gases HX (X = F, Cl, Br). © 2015 Wiley Periodicals, Inc.

Reduction of aryl halides by consecutive visible light-induced electron transfer processes

Biological photosynthesis uses the energy of several visible light photons for the challenging oxidation of water, whereas chemical photocatalysis typically involves only single-photon excitation. Perylene bisimide is reduced by visible light photoinduced electron transfer (PET) to its stable and colored radical anion. We report here that subsequent excitation of the radical anion accumulates sufficient energy for the reduction of stable aryl chlorides giving aryl radicals, which were trapped by hydrogen atom donors or used in carbon-carbon bond formation. This consecutive PET (conPET) overcomes the current energetic limitation of visible light photoredox catalysis and allows the photocatalytic conversion of less reactive chemical bonds in organic synthesis.

Doubling up on optically driven catalysis

Photochemistry During photosynthesis, plants absorb light from the Sun four consecutive times before they accumulate enough energy to make oxygen from water. In contrast, when chemists harness light energy to promote reactivity, they tend to rely on single discrete absorption events. Ghosh et al. now show that a particular dye molecule can channel the combined energy from two absorbed photons to the reduction and subsequent coupling reactions of aryl halide molecules. The method expands the reach of photocatalysis to a broader range of compounds, such as chlorides, which are too stable to breach with a single photon. Science , this issue p. [725][1] [1]: /lookup/doi/10.1126/science.1258232

Molecular tunnelling ionization of allyl halides induced by phase-controlled two-colour laser fields

We have investigated the molecular tunnelling ionization (TI) of four allyl halide molecules (C3H5X; X = F, Cl, Br, I) induced by phase-controlled two-colour laser fields consisting of a fundamental light and a second-harmonic light with a pulse duration of 130 fs and an intensity of 1012–1013 W cm−2. The geometric structure of the highest occupied molecular orbital (HOMO) of the four allyl halides can be systematically changed by replacing the halogen atom. We observed phase-dependent orientation-selective molecular ionization in the four methyl halide molecules. The mechanism of molecular TI is discussed in connection with the geometric structure of the HOMO.

Interaction of N-hydroxyurea with strong proton donors: HCl and HF

An infrared spectroscopic and MP2/6-311++G(2d,2p) study of strong hydrogen bonded complexes of N-hydroxyurea (NH2CONHOH) with hydrogen halides (HCl and HF) trapped in solid argon matrices is reported. 1:1 and 1:2 complexes between N-hydroxyurea and hydrogen chloride, hydrogen fluoride have been identified in the NH2CONHOH/HCl/Ar, NH2CONHOH/HF/Ar matrices, respectively; their structures were determined by comparison of the spectra with the results of calculations. In the 1:1 complexes, identified for both hydrogen halide molecules, the cyclic structure stabilized by the X–H⋯O and N–H⋯X bonds is present; for the NH2CONHOH⋯HF system another isomeric 1:1 complex is also observed. Two 1:2 complexes were identified for the N-hydroxyurea–hydrogen chloride system characterised by the Cl–H⋯O and N–H⋯Cl bonds. The results of the study evidence that N-hydroxyurea is an oxygen base in the gas-phase with the carbonyl group as the strongest proton acceptor centre in the molecule.

Triangular Halogen Bond and Hydrogen Bond Supramolecular Complex Consisting of Carbon Tetrabromide, Halide, and Solvent Molecule: A Theoretical and Spectroscopic Study

The theoretical calculation and spectroscopic experiments indicate a kind of triangular three bonding supramolecular complexes CBr4…X−…H-C, which consist of carbon tetrabromide, halide, and protic solvent molecule (referring to dichloromethane, chloroform and acetonitrile), can be formed in solution. The strength of halogen and hydrogen bonds in the triangular complexes using halide as common acceptor obeys the order of iodide>bromide>chloride. The halogen and hydrogen bonds work weak-cooperatively. Charge transfer bands of halogen bonding complexes between CBr4 and halide are observed in UV-Vis absorption spectroscopy in three solvents, and then the stoichiometry of 1:1, formation constants K and molar extinction coefficients ε of the halogen bonding complexes are obtained by Benesi-Hildebrand method. The K and ε show a dependence on the solvent dielectric constant and, on the whole, obey an order of iodide>bromide>chloride in the same solvents. Furthermore, the C-H vibrational frequencies of solvent molecules vary obviously with the addition of halide, which indicates the C-H…X− interaction. The experimental data indicate that the halogen bond and hydrogen bond coexist by sharing a common halide acceptor as predicted by calculation.

Influence of Shell Thickness and Surface Passivation on PbS/CdS Core/Shell Colloidal Quantum Dot Solar Cells

Cation-exchange has been used to synthesize PbS/CdS core/shell colloidal quantum dots from PbS starting cores. These were then incorporated as the active material in solar cell test devices using a solution-based, air-ambient, layer-by-layer spin coating process. We show that core/shell colloidal quantum dots can replace their unshelled counterparts with a similar band gap as the active layer in a solar cell device, leading to an improvement in open circuit voltage from 0.42 to 0.66 V. This improvement is attributed to a reduction in recombination as a result of the passivating shell. However, this increase comes at the expense of short circuit current by creating a barrier for transport. To overcome this, we first optimize the shell thickness by varying the conditions for cation-exchange to form the thinnest shell layer possible that provides sufficient surface passivation. Next, ligand exchange with a combination of halide and bifunctional organic molecules is used in conjunction with the core/shell str...

Partial hydration of n-alkyl halides at the water–vapor interface: a molecular simulation study with atmospheric implications

Classical molecular dynamics simulations with a polarizable force field were used to study adsorption of gas-phase alkyl halides to the surface of liquid water and their hydration properties in the interfacial environment. A systematic investigation has been performed for a set of monosubstituted alkyl chlorides, bromides and iodides of the alkyl chain length from one to five carbon atoms (C n H2n+1X, n = 1–5, X = Cl, Br, or I). All alkyl halides readily adsorb to the water surface and exhibit a strong preference for interfacial (partial) hydration. When adsorbed, the alkyl halide molecules reside primarily in the outermost region of the water–vapor interface. The (incomplete) hydration shell of the surface-adsorbed methyl halide species is centered on the methyl end of the molecule, with the halogen atom largely exposed and facing away from water into the gas phase. The maximum hydration of the longer-chain alkyl halides is localized around the α-CH2 group next to the halogen. With an increasing chain length, the alkyl halide molecules align more parallel to the surface. However, ethyl and propyl halides still have the halogen atom rather exposed, pointing almost freely into the gas phase. The behavior of butyl and pentyl halides on the water surface resembles that of alcohols, with the polar region of the CH2X group interacting with water and the rest of the increasingly nonpolar hydrocarbon chain pointing on average away from water. Consequently, the halogen atom becomes more, albeit not fully, hydrated. The propensity of alkyl halides for the water–vapor interface along with the specific character of the partial hydration of the surface-adsorbed alkyl halides and their preferred interfacial orientation is likely to be of importance for heterogeneous chemical processes, involving alkyl halides adsorbed on the surface of aqueous aerosol droplets or ice particles in the atmosphere.

Reactions between cold methyl halide molecules and alkali-metal atoms

We investigate the potential energy surfaces and activation energies for reactions between methyl halide molecules CH3X (X = F, Cl, Br, I) and alkali-metal atoms A (A = Li, Na, K, Rb) using high-level ab initio calculations. We examine the anisotropy of each intermolecular potential energy surface (PES) and the mechanism and energetics of the only available exothermic reaction pathway, CH3X + A → CH3 + AX. The region of the transition state is explored using two-dimensional PES cuts and estimates of the activation energies are inferred. Nearly all combinations of methyl halide and alkali-metal atom have positive barrier heights, indicating that reactions at low temperatures will be slow.

Students' understanding of alkyl halide reactions in undergraduate organic chemistry

Organic chemistry is an essential subject for many undergraduate students completing degrees in science, engineering, and pre-professional programs. However, students often struggle with the concepts and skills required to successfully solve organic chemistry exercises. Since alkyl halides are traditionally the first functional group that is studied in undergraduate organic chemistry courses, establishing a robust understanding of the concepts and reactions related to them can be beneficial in assuring students' success in organic chemistry courses. Therefore, the purpose of this study was to elucidate and describe students' understanding of alkyl halide reactions in an undergraduate organic chemistry course. Participants were interviewed using a think-aloud protocol in which they were given a set of questions dealing with reactions and mechanisms of alkyl halide molecules in order to shed light on the students' understanding of these reactions and elucidate any gaps in understanding and incorrect warrants that may be present. These interviews were transcribed and analyzed using a qualitative inquiry approach and a modified Toulmin scheme. In general, the findings from this study show that the students exhibited gaps in understanding and incorrect warrants dealing with: (1) classifying substances as bases and/or nucleophiles, (2) assessing the basic or nucleophilic strength of substances, and (3) accurately describing the steps that take place and reactive intermediates that form during alkyl halide reaction mechanisms. In addition, implications for teaching and future research are discussed.

Addition of allyl halides to the new bis-o-amidophenolate gallium(III) complex

The synthesis and characterization of the new bis-o-amidophenolate gallium(III) complex are reported. This compound was found to be reactive towards allyl halides at room temperature. The addition of two allyl halide molecules to the original complex accompanied with two new C–C bonds formation has been observed. The structures of the products obtained were confirmed by 1H NMR and X-ray diffraction analysis.