Ch 6Haloalkanes and Haloarenes — Class 12 Chemistry, concept-first.

Haloalkanes and haloarenes are the two families of compounds formed when one or more hydrogen atoms of a hydrocarbon are replaced by a halogen atom (F, Cl, Br or I).

Haloalkanes and haloarenes are hydrocarbon derivatives in which one or more hydrogen atoms have been replaced by a halogen atom (F, Cl, Br or I), commonly written as X.

Halogen derivatives can first be sorted purely by counting how many halogen atoms their structure contains.

When the halogen atom (X = F, Cl, Br, or I) is bonded to an -hybridised carbon, the resulting monohalo compound falls into one of three categories, depending on exactly what kind of carbon is holding…

When the halogen atom is bonded to an -hybridised carbon instead of an one, the monohalo compound falls into one of two classes.

Halogenated hydrocarbons are named in two parallel systems — the older common (trivial) names, still widely used in the laboratory, and the systematic IUPAC names built on the parent-hydrocarbon rules…

In every haloalkane, a halogen atom (F, Cl, Br or I) is joined to carbon by a single covalent bond. Halogens are considerably more electronegative than carbon, so the shared electron pair of this bond…

Haloalkanes can be built up from several different starting materials, and the route chosen usually depends on which alkyl halide is needed and how pure it must be.

An alcohol's hydroxyl group can be replaced by a halogen atom by treating it with a concentrated halogen acid, a phosphorus halide, or thionyl chloride ().

Alkanes can be chlorinated or brominated directly through a free-radical chain reaction, typically initiated by UV light or heat:

Alkyl iodides are most conveniently prepared not from an alcohol but by swapping the halogen on an existing alkyl chloride or alkyl bromide.

Haloarenes are prepared by two principal routes: direct halogenation of an arene ring, and diazotization of an aromatic amine followed by displacement of the diazonium group.

Pure haloalkanes and haloarenes are colourless. Exposure to light, however, causes bromo- and iodo-compounds to develop colour over time as traces of the free halogen are liberated.

Once a haloalkane or haloarene has been made and characterised, the question that matters most for organic chemistry is what it can be converted into.

A nucleophile is an electron-rich species — it may be a negatively charged ion or a neutral molecule with a lone pair — and it seeks out the electron-deficient carbon of the C—X bond.

Aryl halides (haloarenes) are far less reactive than alkyl halides toward nucleophilic substitution — chlorobenzene, for instance, will not hydrolyse to phenol under the mild conditions that easily co…

Carbon compounds that carry more than one halogen atom are grouped together as polyhalogen compounds. A large number of these find everyday use in industry and agriculture — as solvents, refrigerants,…

Dichloromethane, , better known by its common name methylene chloride, is valued mainly as a solvent:

Trichloromethane, , is universally known as chloroform. Chemically it serves as a solvent for fats, alkaloids, iodine, and a range of other substances.

Triiodomethane, , is commonly called iodoform. It used to be applied as an antiseptic, but the antiseptic action does not actually come from iodoform itself — it comes from the free iodine that iodofo…

Tetrachloromethane, , is universally known as carbon tetrachloride. It is manufactured in bulk for several purposes:

The chlorofluorocarbon compounds derived from methane and ethane are collectively called freons. They are prized industrially for being extremely stable, unreactive, non-toxic, non-corrosive, and easy…

DDT, short for p,p'-dichlorodiphenyltrichloroethane, has the structure

Alkyl and aryl halides may be classified as mono-, di-, or polyhalogen compounds depending on the number of halogen atoms they carry, and, based on where the halogen sits, as alkyl (sp3 C-X), allylic,…

These are the final answers printed at the end of the NCERT chapter. The book gives answers for some intext questions only — every question below links to our complete worked solution.

Higher-order thinking problems from the NCERT Exemplar.

Questions from official CBSE sample papers.