NEET ChemistryUpdated 19 Oct 2026

Haloalkanes and Haloarenes: NEET PYQs and weightage

Haloalkanes and Haloarenes carries 2.4 of 100 Chemistry marks in NEET by past-paper share: 17 of the 707 tagged NEET Chemistry PYQs in the ViJEEta bank (NEET 2013–2026). It ranks 23 of 26 Chemistry chapters.

Take the 25-question Haloalkanes and Haloarenes test Key facts ↓All NEET Chemistry chapters

2.4/100 Weight in Chemistry

Exam importance (2/5, by past-paper share)

17 NEET PYQs

409 Practice questions

385 With measured difficulty

How the weight is computed: this chapter's tagged NEET PYQs divided by all tagged NEET Chemistry PYQs in the bank (17 of 707), times 100, with repeated questions counted once. The bank does not store the year of each NEET question, so none is printed. Computed from the bank at build time. Updated 19 Oct 2026.

Haloalkanes and Haloarenes: key facts for NEET

17 facts the paper keeps asking, each with how it is asked. Copy it onto one page of your notebook: that page is this chapter's handbook.

Classification of C–X compounds
Haloalkanes have X on an $s p^{3}$ carbon; haloarenes have X on an $s p^{2}$ carbon of an aryl ring. Allylic and benzylic halides are $s p^{3}$ $C - X$ ; vinylic and aryl halides are $s p^{2}$ $C - X$ .
Asked as: Classify $C H_{2} = CHCl$ , $C H_{2} = CHC H_{2} Br$ , $C_{6} H_{5} C H_{2} Cl$ as vinylic / allylic / benzylic / aryl.
C–X bond length, enthalpy and dipole moment
$C - X$ bond length rises $C - F 139 < C - Cl 178 < C - Br 193 < C - I 214 pm$ , and bond enthalpy falls $452 > 351 > 293 > 234 kJ mo l^{- 1}$ . The highest dipole moment is $C H_{3} Cl$ ( $1.860 D$ ), not $C H_{3} F$ ( $1.847 D$ ).
Asked as: Which $C H_{3} - X$ has the highest dipole moment / weakest $C - X$ bond.
Alcohol to alkyl halide
$SOC l_{2}$ is preferred because the by-products $S O_{2}$ and $HCl$ are gases and escape, leaving pure $R - Cl$ . With $HCl$ , $1^{\circ}$ and $2^{\circ}$ alcohols need $ZnC l_{2}$ , and the reactivity order is $3^{\circ} > 2^{\circ} > 1^{\circ}$ .
Asked as: Why thionyl chloride is the best reagent for $R - OH \to R - Cl$ .
Finkelstein and Swarts reactions
Finkelstein uses $R - Cl/Br + NaI$ in dry acetone to give $R - I$ , and the $NaCl/NaBr$ precipitate drives the reaction forward (Le Chatelier). Swarts heats $R - Cl/Br$ with $AgF$ , $H g_{2} F_{2}$ , $Co F_{2}$ or $Sb F_{3}$ to give $R - F$ .
Asked as: Match the named reaction to its reagent and product.
Preparation of aryl halides
$C l_{2} /B r_{2}$ with $Fe$ or $FeC l_{3}$ (Lewis acid) gives $ArCl/ArBr$ . Iodination is reversible and needs $HN O_{3}$ or $HI O_{4}$ , and $ArF$ is not made this way. Sandmeyer converts diazonium salt with $CuCl/CuBr$ to $ArCl/ArBr$ , while $ArI$ needs only $KI$ .
Asked as: Aniline $\to$ chlorobenzene reagent; which halogenation needs an oxidising agent.
Boiling and melting points
Boiling point order is $RI > RBr > RCl > RF$ , and it falls with branching (2-bromo-2-methylpropane is lowest of the three isomers). $p$ -Dihalobenzene melts highest because its symmetry fits the crystal lattice better.
Asked as: Arrange in increasing b.p. / why $p$ -dichlorobenzene has the higher m.p.
Ambident nucleophiles
$C N^{-}$ and $N O_{2}^{-}$ are ambident nucleophiles. $KCN$ (ionic) gives $RCN$ , but $AgCN$ (covalent) gives $RNC$ . $KN O_{2}$ gives the alkyl nitrite $R - O - N = O$ , but $AgN O_{2}$ gives the nitroalkane $R - N O_{2}$ .
Asked as: Major product of $R - X$ with $AgCN$ vs $KCN$ , or $AgN O_{2}$ vs $KN O_{2}$ .
SN2 mechanism
$S_{N} 2$ follows second-order kinetics in one step with no intermediate (C is bonded to five atoms in the transition state). It gives inversion of configuration, with reactivity $C H_{3} X > 1^{\circ} > 2^{\circ} > 3^{\circ}$ set by steric hindrance (Hughes and Ingold, 1937).
Asked as: Arrange bromides for $S_{N} 2$ rate; $(-)$ -2-bromooctane $+ NaOH \to (+)$ -octan-2-ol shows inversion.
SN1 mechanism
$S_{N} 1$ follows first-order kinetics in two steps (slow step makes the carbocation) and works best in polar protic solvents. The order is $3^{\circ} > 2^{\circ} > 1^{\circ}$ , allylic and benzylic halides are very reactive, and optically active halides give racemisation. In both $S_{N} 1$ and $S_{N} 2$ , $R - I > R - Br > R - Cl ≫ R - F$ .
Asked as: Why $S_{N} 1$ on optically active 2-bromobutane gives $(\pm)$ -butan-2-ol.
Chirality and enantiomers
A carbon with four different groups is asymmetric (stereocentre). Butan-2-ol and 2-chlorobutane are chiral, while propan-2-ol is achiral. Enantiomers share all physical properties except the direction of rotating plane-polarised light.
Asked as: Identify the chiral molecule; what property differs between enantiomers.
Racemic mixture
A racemic mixture ( $d l$ or $\pm$ ) has equal enantiomers and zero optical rotation. The sign of rotation ( $+ / -$ ) is not tied to the actual configuration.
Asked as: Optical rotation of a racemic mixture; retention can still change the sign.
Elimination (Zaitsev's rule)
Alcoholic $KOH$ removes H from the $β$ -carbon ( $β$ -elimination). Zaitsev's rule says the more substituted alkene is major, so 2-bromopentane gives pent-2-ene. Aqueous $KOH$ gives alcohols instead.
Asked as: Major alkene on dehydrohalogenation; aqueous vs alcoholic $KOH$ product.
Grignard reagent and Wurtz reaction
Grignard reagent $RMgX$ (Victor Grignard, 1900) forms from $R - X$ and $Mg$ in dry ether. Water, alcohols or amines convert it to a hydrocarbon. Wurtz ( $Na$ /dry ether) joins two R groups, doubling the carbon count.
Asked as: Why Grignard reagent needs anhydrous conditions; $C H_{3} Br + Na$ /dry ether product.
Low reactivity of aryl halides
Aryl halides resist nucleophilic substitution for four reasons: resonance gives $C - Cl$ partial double bond character, $s p^{2}$ carbon holds the bond tighter ( $C - Cl$ $169 pm$ vs $177 pm$ in haloalkane), the phenyl cation is unstable, and the electron-rich ring repels nucleophiles.
Asked as: Why chlorobenzene is less reactive than chloroalkane towards nucleophiles.
Chlorobenzene to phenol
Chlorobenzene becomes phenol with aqueous $NaOH$ at $623 K$ and $300 atm$ . $- N O_{2}$ at ortho/para speeds the reaction, but at meta it has no effect.
Asked as: Conditions for chlorobenzene $\to$ phenol; which nitro-chlorobenzene reacts fastest.
Electrophilic substitution and Wurtz-Fittig/Fittig
Halogen is deactivating ( $- I$ ) yet ortho/para-directing (resonance), since inductive effect controls reactivity and resonance controls orientation. $Na$ /dry ether gives alkylarene (Wurtz-Fittig) or biaryl (Fittig).
Asked as: Why Cl is $o, p$ -directing despite withdrawing electrons; benzene $\to$ biphenyl route.
Polyhalogen compounds
Chloroform is oxidised by air in light to phosgene ( $COC l_{2}$ ), so it is stored in dark bottles filled completely. Freon 12 is $CC l_{2} F_{2}$ , made from $CC l_{4}$ by Swarts. DDT was found effective as an insecticide by Paul Müller (Nobel 1948). Iodoform's antiseptic action comes from free iodine.
Asked as: Poisonous gas from chloroform storage; formula of freon 12; source of iodoform's antiseptic action.

Trap

SN1 and SN2 run in opposite orders. SN2 is 1° > 2° > 3° with inversion, and SN1 is 3° > 2° > 1° with racemisation. Students swap them, especially for benzylic and allylic halides. Only the halide order (R–I > R–Br > R–Cl > R–F) is the same in both.

How does NEET ask Haloalkanes and Haloarenes?

The 17 NEET PYQs in this chapter carry a diagram or a numerical answer, so they are not printed on this page. You meet them in the chapter test and in the PYQ papers.

Which topics in Haloalkanes and Haloarenes carry the most questions?

The 12 busiest of 19 topics, by tagged PYQs, then practice questions. Counted from the bank. Updated 19 Oct 2026.

Topic	PYQs	Practice questions
Nucleophilic Substitution Reaction	5	123
Elimination Reaction	3	92
Chemical Reactions of Aryl Halides	3	27
Chemical Reactions of Alkyl Halides	2	40
Preparation of Aryl Halides	1	8
Classification of Alkyl Halides	1	7
Nomenclature of Alkyl and Aryl Halides	1	7
Introduction to Reaction Mechanism	1	1
Preparation of Alkyl Halides	0	28
Nucleophiles	0	23
Polyhalogen Compounds	0	20
Physical Properties of Alkyl Halides	0	10

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Unknown is not zero. Until you answer at least 3 graded questions in Haloalkanes and Haloarenes, ViJEEta shows – instead of a zero or a 50% default. Book exercises can raise chapter mastery up to 0.60, adaptive practice up to 0.75, and only a timed chapter test or mock can certify 0.80 and above.

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Chapters either side of Haloalkanes and Haloarenes by weight

p-Block Elements (Group 13 and 14) Weight 2.7/100 Practical Chemistry Weight 2.5/100 Gasesous State* Weight 2.1/100 General Organic Chemistry (Revision) and Isomerism Weight 2.0/100

Haloalkanes and Haloarenes: NEET PYQs and weightage

Haloalkanes and Haloarenes: key facts for NEET

Classification of C–X compounds

C–X bond length, enthalpy and dipole moment

Alcohol to alkyl halide

Finkelstein and Swarts reactions

Preparation of aryl halides

Boiling and melting points

Ambident nucleophiles

SN2 mechanism

SN1 mechanism

Chirality and enantiomers

Racemic mixture

Elimination (Zaitsev's rule)

Grignard reagent and Wurtz reaction

Low reactivity of aryl halides

Chlorobenzene to phenol

Electrophilic substitution and Wurtz-Fittig/Fittig

Polyhalogen compounds

How does NEET ask Haloalkanes and Haloarenes?

Which topics in Haloalkanes and Haloarenes carry the most questions?

Why does Haloalkanes and Haloarenes show "–" until you answer 3 questions?

What happens when you test Haloalkanes and Haloarenes?

Chapters either side of Haloalkanes and Haloarenes by weight