Class 12 Chemistry Haloalkanes & Haloarenes Formula Sheet PDF

Ans. You can download the Haloalkanes and Haloarenes Class 12 Chemistry Formula Sheet PDF directly from this Collegedunia page. Both the Normal and HD versions are available and free.

Ans. Yes. This page reflects the current 2026-27 syllabus for Class 12 Chemistry. Haloalkanes and Haloarenes is fully retained in the new edition with no formula cuts; every relation in Sections 6.1 to 6.7 of the NCERT remains examinable.

Ans. The Formula Sheet PDF runs approximately 8 pages and covers the master formula table, symbol glossary, bond-property reference, S_N1 vs S_N2 decision tree, quick-fact MCQ cards, and four common numerical pattern templates.

Ans. The C-I bond enthalpy (234 kJ mol^-1) is much lower than the C-Cl bond enthalpy (351 kJ mol^-1), so the C-I bond breaks more easily. I^- is also a much better leaving group than Cl^- because its larger size disperses the negative charge over a bigger volume. Bond strength, not polarity, sets the reactivity order R-I > R-Br > R-Cl in both S_N1 and S_N2.

Ans. S_N1 is unimolecular with Rate = k[R-X], proceeds via a planar carbocation intermediate, gives racemic product, and is favoured by 3° R-X in polar protic solvents. S_N2 is bimolecular with Rate = k[R-X][Nu^-], proceeds via a single trigonal-bipyramidal transition state, gives Walden inversion, and is favoured by 1° R-X with strong nucleophiles in polar aprotic solvents.

Ans. Sandmeyer: Ar-N₂⁺X^- + Cu₂X₂ → Ar-X + N₂. Gattermann: Ar-N₂⁺X^- + Cu/HX → Ar-X + N₂. Both place a halogen at the exact position of the original -NH₂ group (via the diazonium salt). Sandmeyer uses Cu(I) halide as the catalyst-reagent; Gattermann uses copper powder with HX, which is cheaper but generally lower yield.

Ans. Two reasons. First, the C-X bond in Ar-X is on an sp² C, which is shorter and stronger than the sp³ C-X of haloalkanes (more s-character pulls bonding electrons closer to the nucleus). Second, lone-pair donation from X into the aromatic π system gives the C-X bond partial double-bond character, making it harder to cleave. Together these effects make vinyl and aryl halides virtually inert to S_N1 or S_N2 under normal conditions.

Ans. Saytzeff's rule states that in dehydrohalogenation with a small base (alc. KOH, ethoxide) the major alkene is the more substituted (more stable) one. For example, 2-bromopentane gives pent-2-ene (81 percent) over pent-1-ene (19 percent). Hofmann's rule applies with bulky bases (potassium tert-butoxide): the less-substituted (less hindered) alkene becomes the major product. Saytzeff vs Hofmann is a 2-mark CBSE distinction.

Ans. The Kharasch peroxide effect is the anti-Markovnikov addition of HBr to an unsymmetrical alkene in the presence of organic peroxides (R-O-O-R). The Br radical attaches to the less-substituted (more H-bearing) carbon. The peroxide effect operates only for HBr because only the Br radical chain is energetically favourable; HCl and HI follow regular Markovnikov regardless of peroxide.

Ans. Use the CIP (Cahn-Ingold-Prelog) rules: rank the four substituents on the chiral carbon by atomic number (highest = 1, lowest = 4). Orient the molecule with priority 4 pointing away. Tracing 1 to 2 to 3 clockwise gives R (rectus); anti-clockwise gives S (sinister). For 2-bromobutane: Br > C₂H₅ > CH₃ > H gives the assignment.

Ans. Anhydrous ZnCl₂ + conc. HCl is the Lucas reagent for distinguishing primary, secondary, and tertiary alcohols by converting them to alkyl chlorides. ZnCl₂ is a Lewis acid that polarises the C-O bond and accelerates ionisation. The reagent must be anhydrous because water competes with HCl at the protonation step, slowing the reaction and blurring the cloudiness end-point. Tertiary alcohols turn cloudy at once; secondary in 5-10 min; primary, not at room temperature.

Ans. DDT is prepared by condensing chlorobenzene with chloral (CCl₃CHO) in conc. H₂SO₄. Freons (e.g. CCl₂F₂) are made from CCl₄ by the Swarts reaction using SbF₃/HF or Hg₂F₂. Both bio-accumulate (DDT in fat tissues) or photo-dissociate in the stratosphere releasing Cl radicals that catalytically destroy ozone (CFCs). DDT is banned in most countries; CFCs are phased out under the Montreal Protocol.

Ans. Racemisation is the conversion of an optically active substrate to a 1:1 mixture of (R) and (S) enantiomers (racemic mixture), giving zero net optical rotation. SN1 reactions of chiral substrates cause racemisation because the planar sp² carbocation is attacked by the nucleophile from both faces with equal probability. SN2 by contrast gives complete inversion (Walden inversion).