Fluorocarbons Formally,
fluorocarbons only contain carbon and fluorine. Sometimes they are called perfluorocarbons. They can be gases, liquids, waxes, or solids, depending upon their molecular weight. The simplest fluorocarbon is the gas tetrafluoromethane (CF4). Liquids include perfluorooctane and perfluorodecalin. While fluorocarbons with single bonds are stable, unsaturated fluorocarbons are more reactive, especially those with triple bonds. Fluorocarbons are more chemically and thermally stable than hydrocarbons, reflecting the relative inertness of the C–F bond. They are also relatively
lipophobic. Because of the reduced intermolecular
van der Waals interactions, fluorocarbon-based compounds are sometimes used as lubricants or are highly volatile. Fluorocarbon liquids have medical applications as oxygen carriers. The structure of organofluorine compounds can be distinctive. As shown below, perfluorinated aliphatic compounds tend to segregate from hydrocarbons. This "like dissolves like effect" is related to the usefulness of fluorous phases and the use of
PFOA in processing of fluoropolymers. In contrast to the aliphatic derivatives, perfluoroaromatic derivatives tend to form mixed phases with nonfluorinated aromatic compounds, resulting from donor-acceptor interactions between the pi-systems. between the fluorinated and nonfluorinated rings.
Fluoropolymers Polymeric organofluorine compounds are numerous and commercially significant. They range from fully fluorinated species, e.g.
PTFE to partially fluorinated, e.g.
polyvinylidene fluoride ([CH2CF2]n) and
polychlorotrifluoroethylene ([CFClCF2]n). The fluoropolymer polytetrafluoroethylene (PTFE/Teflon) is a solid.
Hydrofluorocarbons Hydrofluorocarbons (HFCs), organic compounds that contain fluorine and hydrogen atoms, are the most common type of organofluorine compounds. They are commonly used in
air conditioning and as
refrigerants in place of the older
chlorofluorocarbons such as
R-12 and hydrochlorofluorocarbons such as
R-21. They do not harm the ozone layer as much as the compounds they replace; however, they do contribute to
global warming. Their atmospheric concentrations and contribution to
anthropogenic greenhouse gas emissions are rapidly increasing, causing international concern about their
radiative forcing. Fluorocarbons with few C–F
bonds behave similarly to the parent hydrocarbons, but their reactivity can be altered significantly. For example, both
uracil and
5-fluorouracil are colourless, high-melting crystalline solids, but the latter is a potent anti-cancer drug. The use of the C–F bond in pharmaceuticals is predicated on this altered reactivity. Several drugs and
agrochemicals contain only one fluorine center or one
trifluoromethyl group. Unlike other greenhouse gases in the
Paris Agreement, hydrofluorocarbons have other international negotiations. In September 2016, the so-called New York Declaration urged a global reduction in the use of HFCs. On 15 October 2016, due to these chemicals contribution to
climate change, negotiators from 197 nations meeting at the summit of the
United Nations Environment Programme in Kigali, Rwanda reached a legally binding accord to phase out hydrofluorocarbons (HFCs) in an amendment to the
Montreal Protocol.
Fluorocarbenes As indicated throughout this article, fluorine-substituents lead to reactivity that differs strongly from classical organic chemistry. The premier example is
difluorocarbene, CF2, which is a
singlet whereas
carbene (CH2) has a
triplet ground state. This difference is significant because difluorocarbene is a precursor to
tetrafluoroethylene.
Perfluorinated compounds Perfluorinated compounds are fluorocarbon derivatives, as they are closely structurally related to fluorocarbons. However, they also possess
nitrogen,
iodine, or
oxygen.
Perfluorinated carboxylic acids are examples. Highly fluorinated substituents, e.g. perfluorohexyl (C6F13) confer distinctive solubility properties to molecules, which facilitates purification of products in
organic synthesis. This area, described as "
fluorous chemistry," exploits the concept of like-dissolves-like in the sense that fluorine-rich compounds dissolve preferentially in fluorine-rich solvents. Because of the relative inertness of the C–F bond, such fluorous phases are compatible with harsh reagents. This theme has spawned techniques of
fluorous tagging and
fluorous protection. Illustrative of fluorous technology is the use of fluoroalkyl-substituted tin hydrides for reductions, the products being easily separated from the spent tin reagent by extraction using fluorinated solvents.
Triphenylphosphine has been modified by attachment of perfluoroalkyl substituents that confer solubility in
perfluorohexane as well as
supercritical carbon dioxide. As a specific example, [(C8F17C3H6-4-C6H4)3P. Hydrophobic fluorinated
ionic liquids, such as organic salts of
bistriflimide or
hexafluorophosphate, can form phases that are insoluble in both water and organic solvents, producing
multiphasic liquids. Fluorine-containing compounds are often featured in
noncoordinating or weakly coordinating anions. Both tetrakis(pentafluorophenyl)borate, B(C6F5)4−, and the related tetrakis(3,5-bis(trifluoromethyl)phenyl)borate|tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, are useful in
Ziegler–Natta catalysis and related alkene polymerization methodologies. The fluorinated substituents render the anions weakly basic and enhance the solubility in weakly basic solvents, which are compatible with strong Lewis acids. ==Methods for preparation of C–F bonds==