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The halogens are a group in the periodic table consisting of six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and the radioactive elements astatine (At) and tennessine (Ts), though some authors would exclude tennessine as its chemistry is unknown and is theoretically expected to be more like that of gallium. In the modern IUPAC nomenclature, this group is known as group 17.
Fluorocarbons are chemical compounds with carbon-fluorine bonds. Compounds that contain many C-F bonds often have distinctive properties, e.g., enhanced stability, volatility, and hydrophobicity. Several fluorocarbons and their derivatives are commercial polymers, refrigerants, drugs, and anesthetics.
Supramolecular chemistry refers to the branch of chemistry concerning chemical systems composed of a discrete number of molecules. The strength of the forces responsible for spatial organization of the system range from weak intermolecular forces, electrostatic charge, or hydrogen bonding to strong covalent bonding, provided that the electronic coupling strength remains small relative to the energy parameters of the component. While traditional chemistry concentrates on the covalent bond, supramolecular chemistry examines the weaker and reversible non-covalent interactions between molecules. These forces include hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, pi–pi interactions and electrostatic effects.
The term molecular recognition refers to the specific interaction between two or more molecules through noncovalent bonding such as hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, π-π interactions, halogen bonding, or resonant interaction effects. In addition to these direct interactions, solvents can play a dominant indirect role in driving molecular recognition in solution. The host and guest involved in molecular recognition exhibit molecular complementarity. Exceptions are molecular containers, including, e.g., nanotubes, in which portals essentially control selectivity. Selective partioning of molecules between two or more phases can also result in molecular recognition. In partitioning-based molecular recognition the kinetics and equilibrium conditions are governed by the presence of solutes in the two phases.
A halonium ion is any onium ion containing a halogen atom carrying a positive charge. This cation has the general structure R−−R′ where X is any halogen and no restrictions on R, this structure can be cyclic or an open chain molecular structure. Halonium ions formed from fluorine, chlorine, bromine, and iodine are called fluoronium, chloronium, bromonium, and iodonium, respectively. The 3-membered cyclic variety commonly proposed as intermediates in electrophilic halogenation may be called haliranium ions, using the Hantzsch-Widman nomenclature system.
Crystal engineering studies the design and synthesis of solid-state structures with desired properties through deliberate control of intermolecular interactions. It is an interdisciplinary academic field, bridging solid-state and supramolecular chemistry.
Organofluorine chemistry describes the chemistry of organofluorine compounds, organic compounds that contain a carbon–fluorine bond. Organofluorine compounds find diverse applications ranging from oil and water repellents to pharmaceuticals, refrigerants, and reagents in catalysis. In addition to these applications, some organofluorine compounds are pollutants because of their contributions to ozone depletion, global warming, bioaccumulation, and toxicity. The area of organofluorine chemistry often requires special techniques associated with the handling of fluorinating agents.
Hypofluorous acid, chemical formula HOF, is the only known oxyacid of fluorine and the only known oxoacid in which the main atom gains electrons from oxygen to create a negative oxidation state. The oxidation state of the oxygen in this acid is 0, while its valence is 2. It is also the only hypohalous acid that can be isolated as a solid. HOF is an intermediate in the oxidation of water by fluorine, which produces hydrogen fluoride, oxygen difluoride, hydrogen peroxide, ozone and oxygen. HOF is explosive at room temperature, forming HF and O2:
A molecular solid is a solid consisting of discrete molecules. The cohesive forces that bind the molecules together are van der Waals forces, dipole–dipole interactions, quadrupole interactions, π–π interactions, hydrogen bonding, halogen bonding, London dispersion forces, and in some molecular solids, coulombic interactions. Van der Waals, dipole interactions, quadrupole interactions, π–π interactions, hydrogen bonding, and halogen bonding are typically much weaker than the forces holding together other solids: metallic, ionic, and network solids.
The carbon–fluorine bond is a polar covalent bond between carbon and fluorine that is a component of all organofluorine compounds. It is one of the strongest single bonds in chemistry, and relatively short, due to its partial ionic character. The bond also strengthens and shortens as more fluorines are added to the same carbon on a chemical compound. As such, fluoroalkanes like tetrafluoromethane are some of the most unreactive organic compounds.
In chemistry, a halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. Like a hydrogen bond, the result is not a formal chemical bond, but rather a strong electrostatic attraction. Mathematically, the interaction can be decomposed in two terms: one describing an electrostatic, orbital-mixing charge-transfer and another describing electron-cloud dispersion. Halogen bonds find application in supramolecular chemistry; drug design and biochemistry; crystal engineering and liquid crystals; and organic catalysis.
An oxaziridine is an organic molecule that features a three-membered heterocycle containing oxygen, nitrogen, and carbon. In their largest application, oxaziridines are intermediates in the industrial production of hydrazine. Oxaziridine derivatives are also used as specialized reagents in organic chemistry for a variety of oxidations, including alpha hydroxylation of enolates, epoxidation and aziridination of olefins, and other heteroatom transfer reactions. Oxaziridines also serve as precursors to nitrones and participate in [3+2] cycloadditions with various heterocumulenes to form substituted five-membered heterocycles. Chiral oxaziridine derivatives effect asymmetric oxygen transfer to prochiral enolates as well as other substrates. Some oxaziridines also have the property of a high barrier to inversion of the nitrogen, allowing for the possibility of chirality at the nitrogen center.
Hydrodefluorination (HDF) is a type of organic reaction in which in a substrate of a carbon–fluorine bond is replaced by a carbon–hydrogen bond. The topic is of some interest to scientific research. In one general strategy for the synthesis of fluorinated compounds with a specific substitution pattern, the substrate is a cheaply available perfluorinated hydrocarbon. An example is the conversion of hexafluorobenzene (C6F6) to pentafluorobenzene (C6F5H) by certain zirconocene hydrido complexes. In this type of reaction the thermodynamic driving force is the formation of a metal-fluorine bond that can offset the cleavage of the very stable C-F bond. Other substrates that have been investigated are fluorinated alkenes. Another reaction type is oxidative addition of a metal into a C-F bond followed by a reductive elimination step in presence of a hydrogen source. For example, perfluorinated pyridine reacts with bis(cyclooctadiene)nickel(0) and triethylphosphine to the oxidative addition product and then with HCl to the ortho-hydrodefluorinated product. In reductive hydrodefluorination the fluorocarbon is reduced in a series of single electron transfer steps through the radical anion, the radical and the anion with ultimate loss of a fluorine anion. An example is the conversion of pentafluorobenzoic acid to 3,4,5-tetrafluorobenzoic acid in a reaction of zinc dust in aqueous ammonia.
Fluorine forms a great variety of chemical compounds, within which it always adopts an oxidation state of −1. With other atoms, fluorine forms either polar covalent bonds or ionic bonds. Most frequently, covalent bonds involving fluorine atoms are single bonds, although at least two examples of a higher order bond exist. Fluoride may act as a bridging ligand between two metals in some complex molecules. Molecules containing fluorine may also exhibit hydrogen bonding. Fluorine's chemistry includes inorganic compounds formed with hydrogen, metals, nonmetals, and even noble gases; as well as a diverse set of organic compounds. For many elements the highest known oxidation state can be achieved in a fluoride. For some elements this is achieved exclusively in a fluoride, for others exclusively in an oxide; and for still others the highest oxidation states of oxides and fluorides are always equal.
Pierangelo Metrangolo is an Italian chemist with interests in supramolecular chemistry and functional materials. He also has an interest in crystal engineering, in particular by using the halogen bond. He is Vice-President and President-Elect of the Physical and Biophysical Chemistry Division of IUPAC.
In chemistry, a chalcogen bond (ChB) is an attractive interaction in the family of σ-hole interactions, along with halogen bonds. Electrostatic, charge-transfer (CT) and dispersion terms have been identified as contributing to this type of interaction. In terms of CT contribution, this family of attractive interactions has been modeled as an electron donor interacting with the σ* orbital of a C-X bond of the bond donor. In terms of electrostatic interactions, the molecular electrostatic potential (MEP) maps is often invoked to visualize the electron density of the donor and an electrophilic region on the acceptor, where the potential is depleted, referred to as a σ-hole. ChBs, much like hydrogen and halogen bonds, have been invoked in various non-covalent interactions, such as protein folding, crystal engineering, self-assembly, catalysis, transport, sensing, templation, and drug design.
Nonafluoro-tert-butyl alcohol is a fluoroalcohol. It is the perfluorinated analog of tert-butyl alcohol. Notably, as a consequence of its electron withdrawing fluorine substituents, it is very acidic for an alcohol, with a pKa value of 5.4, similar to that of a carboxylic acid. As another consequence of being a perfluorinated compound, it is also one of the lowest boiling alcohols, with a boiling point lower than that of methanol.
Diiodoacetylene is the organoiodine compound with the formula C2I2. It is a white, volatile solid that dissolves in organic solvents. It is prepared by iodination of trimethylsilylacetylene. Although samples explode above 80 °C, diiodoacetylene is the most readily handled of the dihaloacetylenes. Dichloroacetylene, for example, is more volatile and more explosive. As confirmed by X-ray crystallography, diiodoacetylene is linear. It is however a shock, heat and friction sensitive compound. Like other haloalkynes, diiodoacetylene is a strong halogen bond donor.
In chemistry, sigma hole interactions are a family of intermolecular forces that can occur between several classes of molecules and arise from an energetically stabilizing interaction between a positively-charged site, termed a sigma hole, and a negatively-charged site, typically a lone pair, on different atoms that are not covalently bonded to each other. These interactions are usually rationalized primarily via dispersion, electrostatics, and electron delocalization and are characterized by a strong directional preference that allows control over supramolecular chemistry.
In chemistry, a pnictogen bond (PnB) is a non-covalent interaction, occurring where there is a net attractive force between an electrophilic region on a 'donor' pnictogen atom (Pn) in a molecule, and a nucleophilic region on an 'acceptor' atom, which may be in the same or another molecule. Closely related to halogen and chalcogen bonding, pnictogen bonds are a form of non-covalent interaction which can be considered in terms of charge-transfer and electrostatic interactions.
References
- ↑ "RCS News, June 2011, pag. 30: RCS-SCI Award to Giuseppe Resnati" (PDF).
- ↑ "ICNI-2022, The van der Waals Prize".
- ↑ Halogen Bonding: Fundamentals and Applications Metrangolo, P. and Resnati, G. Eds.; 2008; Springer; Berlin, Heidelberg, New York. ISBN 978-3-540-74329-3
- ↑ G. Resnati et al. The Chalcogen Bond in Crystalline Solids: A World Parallel to Halogen Bond Accounts of Chemical Research 2019, 52, 1311-1324 (DOI: org/10.1021/acs.accounts.9b00037)
- ↑ G. Resnati et al. Definition of the pnictogen bond (IUPAC Recommendations 2023) Pure and Applied Chemistry 2024, 96, 135-145 (DOI: org/10.1515/pac-2020-1002)
- ↑ G. Resnati et al. Naming Interactions from the Electrophilic Site Cryst. Growth & Des. 2014, 96, 135-145 (DOI: org/0.1021/cg5001717)
- ↑ G. Resnati Synthesis of Chiral and Bioactive Fluoroorganic Compounds Tetrahedron 1993, 49, 9385-9445 (DOI:10.1016/S00404020(01)80212-X)
- ↑ G. Resnati et al. Perfluorinated Oxaziridines: Synthesis and Reactivity Chemical Reviews 1996, 96, 1809-1824 (DOI: 10.1021/cr941146h)
- ↑ G. Resnati et al. 19F Magnetic Resonance Imaging (MRI): From Design of Materials to Clinical Applications Chemical Reviews 2015, 115, 1106−1129 (DOI: org/10.1021/cr500286d)
- ↑ "Resnati coordinated an IUPAC project on crystal engineering".
- ↑ G. Resnati et al. Halogen Bonding in Supramolecular Chemistry Angew. Chem. Int. Ed. 2008, 47, 6114-6127 ( DOI: 10.1002/anie.200800128 )
- ↑ G. Resnati et al. Halogen bonded Borromean networks by design: topology invariance and metric tuning in a library of multi-component systems Chemical Sci. 2017 ( DOI: 10.1039/C6SC04478F )
- ↑ G. Resnati et al. Halogen Bonding Based Recognition Processes: A World Parallel to Hydrogen Bonding Acc. Chem. Res. 2005, 38, 386-395 (DOI: 10.1021/ar0400995 )
- ↑ G. Resnati et al. An Adaptable and Dynamically Porous Organic Salt Traps Unique Tetrahalide Dianions Angew. Chem. Int. Ed. 2013, 52, 13444-13448 ( DOI: 10.1002/anie.201307552 )
- ↑ G. Resnati et al. Halogen-bonding-triggered supramolecular gel formation Nature Chem. 2013, 5, 42-47 ( DOI:10.1038/nchem.1496 )
- ↑ Halogen Bonding I - Impact on Materials Chemistry and Life Sciences Metrangolo P. and Resnati G. Eds.; 2014; Springer; Berlin, Heidelberg, New York. ISBN 978-3-319-14056-8
- ↑ Halogen Bonding II - Impact on Materials Chemistry and Life Sciences Metrangolo P. and Resnati G. Eds.; 2015; Springer; Berlin, Heidelberg, New York. ISBN 978-3-319-15731-3
- ↑ "ICNI-2022, The van der Waals Prize".
- ↑ "RCS News, June 2011, pag. 30: RCS-SCI Award to Giuseppe Resnati" (PDF).
- ↑ "Intermolecular Interactions and Structural Aspects in Organic Chemistry awards" (PDF).
- ↑ "Academy of Europe: Resnati Giuseppe".
- ↑ Journal of Fluorine Chemistry: Editorial Board.
- ↑ Rogers, Robin D. (2012). "Crystal Growth & Design Around the World in 2012, DOI:10.1021/cg201654d". Crystal Growth & Design. 12: 1–2. doi: 10.1021/cg201654d .
- ↑ "ISXB-1".
- ↑ "Official Web-site of the Faraday Discussion".
- ↑ "Rotary Club Morimondo Abbazia".
- ↑ "L'Orma, anno XL, N.1, Marzo 2022" (PDF).
- ↑ "Order of the Holy Sepulchre of Jerusalem".
- ↑ "Sacred Military Constantinian Order of Saint George (Spain)".
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