The fluorine atom has the largest electronegativity and the smallest atomic radius except hydrogen, which determines its unique physical and chemical properties. Due to the unique electronegativity, electronic effect and steric hindrance effect of fluorine atoms, the reactions of organic fluorine chemistry often show different characteristics and laws from conventional organic reactions, so it has unique academic research value; in addition, fluorine-containing organic compounds are generally present Some unique physical and chemical properties, such as high physical and chemical stability, fluorocarbon phase and unique biological activity, determine its wide application in the fields of materials, medicine and energy.
The macroscopic physical properties of organic fluorine-containing compounds are determined by their microscopic molecular structure and intermolecular interactions. The C-F bond has lower HOMO and LUMO energy levels, which determines its "easy reduction, difficult oxidation" reaction Sexual characteristics. Because the HOMO energy of the C-F bond is low, it shows that the nucleus has a strong binding effect on valence electrons, and the electron cloud distribution is not easily affected by the outside world, that is, the polarization ability is weak. Polarizability directly affects the intermolecular forces and indirectly affects the macroscopic physical properties of organic fluorine compounds such as boiling point, solubility, fat solubility, surface tension and dielectric constant.
The boiling point of fluorochemicals is usually lower than that of non-fluorine analogues. The boiling point is generally related to intermolecular forces, while fluorine-containing compounds have poor polarization and weak intermolecular forces.
In addition to the water phase and organic phase, perfluorinated compounds have a unique "fluorocarbon phase". The interaction between perfluorinated compounds and other compounds is weak, so they can form a phase by themselves. Organic compounds containing multiple fluorine atoms have good solubility in perfluorinated solvents, and fluorocarbon phase chemistry is widely used in the fields of catalyst recovery and separation of fluorine-containing compounds. In addition, fluorine-containing solvents have a stronger ability to dissolve gases than conventional solvents.
Generally speaking, the fluorine-containing group attached to the sp2 carbon can increase the lipophilicity, while the fluorine-containing group attached to the sp3 carbon can reduce the lipophilicity. In addition, fluorine-containing groups connected to heteroatoms or conjugated systems can also improve lipophilicity.
The force that promotes the contraction of the liquid surface is called surface tension, and most of the fluorine-containing compounds can reduce the surface tension. Fluorocarbon surfactants have high surface activity, high thermodynamics and chemical stability, and have applications in many fields.
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