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Interhalogens are typically more reactive than all diatomic halogen molecules except F 2 because interhalogen bonds are weaker. However, the chemical properties of interhalogens are still roughly the same as those of diatomic halogens. Many interhalogens consist of one or more atoms of fluorine bonding to a heavier halogen.
Aliphatic compounds can be saturated, joined by single bonds (), or unsaturated, with double bonds or triple bonds ().If other elements (heteroatoms) are bound to the carbon chain, the most common being oxygen, nitrogen, sulfur, and chlorine, it is no longer a hydrocarbon, and therefore no longer an aliphatic compound.
Halogens are so named due to their potential to form salts, and form many simple strong acids with hydrogen. Out of the four stable halogens, only fluorine and chlorine have reduction potentials higher than that of oxygen, allowing them to form hydrofluoric acid and hydrochloric acid directly through reaction with water. [17]
The addition of halogens to alkenes proceeds via intermediate halonium ions. In special cases, such intermediates have been isolated. [5] Bromination is more selective than chlorination because the reaction is less exothermic. Illustrative of the bromination of an alkene is the route to the anesthetic halothane from trichloroethylene: [6]
Phenylic hydrogens have extremely strong bonds and are rarely displaced by halogens. Non-enolizable aldehydes oxidize to the acyl halide, but enolizable aldehydes typically halogenate at the α position instead. Indeed, allylic and benzylic hydrogens have bonds much weaker than alkanes, and are selectively replaced in the Wohl-Ziegler reaction.
Haloalkanes containing halogens other than fluorine are more reactive than the parent alkanes—it is this reactivity that is the basis of most controversies. Many are alkylating agents , with primary haloalkanes and those containing heavier halogens being the most active (fluoroalkanes do not act as alkylating agents under normal conditions).
The reaction most often occurs at an aliphatic sp 3 carbon center with an electronegative, stable leaving group attached to it, which is frequently a halogen (often denoted X). The formation of the C–Nu bond, due to attack by the nucleophile (denoted Nu), occurs together with the breakage of the C–X bond.
By the same token, however, since iodine has the lowest ionisation energy among the halogens and is the most easily oxidised of them, it has a more significant cationic chemistry and its higher oxidation states are rather more stable than those of bromine and chlorine, for example in iodine heptafluoride. [1]