hydrohalische

Hydrohalische, or hydrohalic, compounds are chemical species formed from hydrogen and a halogen. The term can refer to two related classes: hydrogen halides (HX) in the gas phase or in solution, and the corresponding salts formed when hydrogen halides or halide ions combine with metals or other cations. In practice, the most commonly discussed examples are hydrogen chloride, hydrogen bromide, hydrogen iodide, and hydrogen fluoride, along with their salts.

Hydrogen halides in water are known as hydrohalic acids. In aqueous solution, HCl, HBr, and HI are strong acids that dissociate nearly completely, making solutions highly acidic. HF is an exception: it is a relatively weak acid in water due to the unusually strong H–F bond and extensive hydrogen bonding, with a pKa around 3.2. The acidity trend in aqueous solution increases from HF to HI, reflecting bond strength and anion stability. In the gas phase, HX molecules exist as diatomic species, and their acid-base behavior differs from that in water.

Hydrohalides are salts containing a halide anion or cationic metal/organic partners. Common inorganic hydrohalides include NaCl, KBr, and other metal halides, many of which are soluble in water and widely used in industry and daily life. In organic chemistry, hydrogen halides can add to unsaturated substrates in hydrohalogenation, converting alkenes or alkynes into alkyl halides with regiochemical preferences described by Markovnikov’s rule.

Overall, hydrohalische compounds play a foundational role in acid-base chemistry, materials science, and organic synthesis.