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CBSE Class 12 · Chemistry

Haloalkanes and Haloarenes

Official NCERT chapter from Chemistry Part I–II (book code lech1). ExamMaster notes are original teaching at CBSE Class 12 depth.

This lesson follows the official chapter “Haloalkanes and Haloarenes” in Chemistry Part I–II. The words below are ExamMaster’s teaching, not a paste from the book. Use the NCERT chapter for the classroom sequence; use these notes to hold the idea without copying exercises or figures.

  • CBSE Class 12
  • Medium level
  • 8 concepts

1Classification

Classification: alkyl (haloalkane), allylic, benzylic, aryl (haloarene) as taught. A class is a carbon-look next to X, not a smell. C–X on an alkane-chain versus on a benzene ring is the big split.

Calling every C–X a haloarene because “organic” is a steal.

Figure. First split is where the halogen sits: alkyl carbon (haloalkane) versus aryl carbon (haloarene). Haloalkanes then split by how many carbons touch the C–X carbon: 1°, 2°, 3°.

How it works

  1. Look at the carbon that holds XThe classify.
  2. Name haloalkane or haloarene (or the extra type)The class.
  3. Refuse a smell as the testA carbon-look.

2Nomenclature

Nomenclature: the taught IUPAC — halo as a prefix, lowest locant. CH3CH2Br is bromoethane. A name is a rule-output, not a brand (ethyl bromide if the lesson still allowed it).

Numbering from the pretty end so Br sits at 5 is a miss.

Figure. IUPAC numbers the longest chain so the halogen gets the lowest locant. Four carbons in a row with Br on the second carbon is 2-bromobutane, not 3-bromobutane counted from the other end.

How it works

  1. Find the chain and the haloThe given.
  2. Give X the lowest locant as taughtThe name.
  3. Keep it systematicNot a brand.

3Nature of C–X Bond

Nature of C–X: polar as taught, C δ+ and X δ−. Bond length and strength trend down the group if named. Nature is a polarity-look, not a colour.

A C–H as polar-as-C–X is a miss.

Figure. X is more electronegative than carbon, so the bonding pair sits nearer X. Carbon is δ+, the halogen is δ−, and that polarity is why a nucleophile aims at carbon.

How it works

  1. Name C δ+ next to XThe nature.
  2. Keep a down-group trend only if taughtHonest extra.
  3. Refuse a colour as the testA polarity.

4Methods of Preparation of Haloalkanes

Preparation of haloalkanes: from alcohols (HX or PCl5 as taught) or from alkanes if listed. Preparation is a from-what, not a use. One school route is enough.

A haloarene route labelled haloalkane is a swap.

Figure. Three school routes into a haloalkane: alcohol plus HX or SOCl₂, alkene plus HX, and free-radical halogenation of an alkane. All three end at R–X; they do not start from the same feedstock.

How it works

  1. Name the starting look (alcohol, …)The from.
  2. Name the taught reagentThe route.
  3. Keep it an alkyl-XThis heading.

5Preparation of Haloarenes

Preparation of haloarenes: electrophilic substitution on benzene as taught (halogen + Lewis acid if framed), or from a diazonium if listed. Haloarene is a ring-X, not an alkyl-X route.

An alcohol+HX as the default haloarene is a miss.

Figure. Haloarenes at this class come two ways: Sandmeyer (aniline to diazonium to ArX with CuX) and electrophilic halogenation of the ring with X₂ and FeX₃. No ring drawing is needed to keep the routes apart.

How it works

  1. Name the ring-startThe from.
  2. Name the taught ring-routeThe preparation.
  3. Keep it aryl-XThis heading.

6Physical Properties

Physical properties: boiling trends and density as taught; water-mix is poor as framed. Physical is a look, not a reaction. One trend (bp rises with mass) is enough.

A reaction-mechanism as a physical property is a swap.

Figure. Boiling point of CH₃X rises as X gets heavier: chloromethane is a gas below 0 °C, bromomethane just above, iodomethane much higher. Same carbon, larger halogen, stronger London forces.

How it works

  1. Name bp, density, or mix as taughtThe property.
  2. Keep one trendThe look.
  3. Refuse a mechanism herePhysical.

7Chemical Reactions

Chemical reactions: nucleophilic substitution on haloalkanes as taught (SN1/SN2 if named); haloarenes sit less ready as framed. Elimination if listed. Reaction is a who-replaces-X, not a physical boil.

Treating a haloarene as equally ready as a primary alkyl halide is a miss if the lesson split them.

Figure. Nucleophilic substitution splits by timing. SN2 is one step on a 1° carbon; SN1 is two steps through a 3° cation. The halogen leaves in both; the path is what the class tests.

How it works

  1. Name the carbon-look (alkyl vs aryl)The given.
  2. Name substitution (or elimination) as taughtThe reaction.
  3. Keep aryl as the less-ready look if taughtHonest.

8Polyhalogen Compounds

Polyhalogen compounds: CHCl3, CHI3, freons, DDT as taught — a named use or a caution-sentence. Polyhalogen is a many-X case, not a how-to. School-size only; no extra private how-to.

A scare-poster with no named compound is a mute caution.

Figure. Polyhalogen compounds are named for a use, not a new functional-group family. Chloroform as a solvent, iodoform as an antiseptic, a freon as a coolant, DDT as a banned insecticide.

How it works

  1. Name the taught compoundThe case.
  2. Attach a use or a caution as framedThe sentence.
  3. Refuse a how-toThis class.
Bromoethane is
  1. A haloalkane — X on an alkyl carbon
  2. A haloarene
  3. A metal carbonyl

The carbon-look.

Notes

  • Mapped to the official NCERT chapter “Haloalkanes and Haloarenes”. Original teaching only — no textbook sentences.
  • Science here is Physics, Chemistry and Biology ideas at this class, never a language or social-science chapter.

Formulas

  • haloalkane: X on alkyl carbon
  • haloarene: X on aryl carbon

Recap

Hold these pegs from the official chapter “Haloalkanes and Haloarenes”. The wording is ExamMaster’s teaching, not a textbook recap.

Classification
Classification: alkyl (haloalkane), allylic, benzylic, aryl (haloarene) as taught.
Nomenclature
Nomenclature: the taught IUPAC — halo as a prefix, lowest locant.
Nature of C–X Bond
Nature of C–X: polar as taught, C δ+ and X δ−.
Methods of Preparation of Haloalkanes
Preparation of haloalkanes: from alcohols (HX or PCl5 as taught) or from alkanes if listed.
Preparation of Haloarenes
Preparation of haloarenes: electrophilic substitution on benzene as taught (halogen + Lewis acid if framed), or from a diazonium if listed.
Physical Properties
Physical properties: boiling trends and density as taught; water-mix is poor as framed.

Practise Haloalkanes and Haloarenes

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