Галогенталған ароматикалық қосылыстар

Aromatic compounds containing Halogen atom(s) in place of Hydrogen
In organic chemistry, an aryl halide (also known as haloarene) is an aromatic compound in which one or more hydrogen atoms, directly bonded to an aromatic ring are replaced by a halide. The haloarene are different from haloalkanes because they exhibit many differences in methods of preparation and properties. The most important members are the aryl chlorides, but the class of compounds is so broad that there are many derivatives and applications.

Although the term aryl halide includes halogenated derivatives of any aromatic compound, it commonly refers to halobenzenes, which are specifically halogenated derivatives of benzene. Groups of halobenzenes include fluorobenzenes, chlorobenzenes, bromobenzenes, and iodobenzenes, as well as mixed halobenzenes containing at least two different types of halogens bonded to the same benzene ring. There are also many halobenzene derivatives.

Halopyridines are based on the aromatic compound pyridine. This includes chloropyridines and bromopyridines. Chloropyridines are important intermediates to pharmaceuticals and agrochemicals.

Halogenated naphthalenes are based on naphthalene. Polychlorinated naphthalenes were used extensively from the 1930s to 1950s in cable and capacitor production, due to their insulating, hydrophobic, and flame retardant properties, but they have since been phased out for this use due to toxicity, environmental persistence, and introduction of new materials. Synthetic T4 is one of the most heavily prescribed medicines in the U. S.

Many chlorinated and brominated aromatic compounds are produced by marine organisms. The chloride and bromide in ocean waters are the source of the halogens. Various peroxidase enzymes (e. g., bromoperoxidase catalyze the reactions. Numerous are derivatives of electron rich rings found in tyrosine, tryptophan, and various pyrroles. Some of these natural aryl halides exhibit useful medicinal properties.

The C X distances for aryl halides follow the expected trend. These distances for fluorobenzene, chlorobenzene, bromobenzene, and methyl 4 iodobenzoate are 135.6(4), 173.90(23), 189.8(1), and 209.9 pm, respectively.

Unlike typical alkyl halides, aryl halides typically do not participate in conventional substitution reactions. Aryl halides with electron withdrawing groups in the ortho and para positions, can undergo SNAr reactions. For example, 2,4 dinitrochlorobenzene reacts in basic solution to give a phenol:

Unlike in most other substitution reactions, fluoride is the best leaving group, and iodide the worst. A 2018 paper indicates that this situation may actually be rather common, occurring in systems that were previously assumed to proceed via SNAr mechanisms.

Aryl halides often react via the intermediacy of benzynes. Chlorobenzene and sodium amide react in liquid ammonia to give aniline by this pathway.

The halides can be displaced by strong nucleophiles via reactions involving radical anions. Alternatively aryl halides, especially the bromides and iodides, undergo oxidative addition, and thus are subject to Buchwald–Hartwig amination type reactions. Chlorobenzene was once the precursor to phenol, which is now made by oxidation of cumene. At high temperatures, aryl groups react with ammonia to give anilines.