aruülhalogeniide

Aruülhalogeniide, also known as aryl halides, are a class of organic compounds in which a halogen atom is covalently bonded to an aromatic ring. The halogen atom can be fluorine, chlorine, bromine, or iodine. The aromatic ring is typically a benzene ring, but can also be other cyclic, planar molecules with delocalized pi electrons. The bond between the carbon atom of the aromatic ring and the halogen atom is generally strong due to the partial double bond character arising from the resonance between the pi electrons of the ring and the lone pairs on the halogen atom.

Aryl halides exhibit different chemical reactivity compared to alkyl halides. The electron-withdrawing nature of the aromatic ring, combined with resonance effects, makes the carbon-halogen bond less polar and stronger than in alkyl halides. This generally leads to lower reactivity in nucleophilic substitution reactions, particularly SN2 reactions, which are hindered by the steric bulk of the aromatic ring and the partial double bond character. However, aryl halides can undergo nucleophilic aromatic substitution under specific conditions, such as the presence of strong electron-withdrawing groups on the ring or very strong nucleophiles and high temperatures. They are more prone to electrophilic aromatic substitution reactions, where the halogen atom can act as an activating or deactivating group depending on the specific halogen and reaction conditions.

Aryl halides are important intermediates in organic synthesis. They are used in various coupling reactions, such as Suzuki, Heck, and Sonogashira couplings, to form new carbon-carbon bonds, which are fundamental in the synthesis of pharmaceuticals, agrochemicals, and advanced materials. They can also be converted into organometallic reagents, like Grignard reagents or organolithium compounds, which are versatile building blocks in organic chemistry.