CUET UG Chemistry Booster Test -3 Preparation and Physical Properties

The passage clearly states that treatment of a primary aromatic amine with sodium nitrite in cold aqueous mineral acid produces a diazonium salt. This diazonium salt acts as the intermediate which later undergoes substitution reactions to form haloarenes.

Unlike chlorination and bromination, replacement of the diazonium group by iodine occurs simply by treating the diazonium salt with potassium iodide. The iodide ion directly replaces the diazonium group, eliminating the need for a cuprous halide catalyst.

Reactivity towards haloacids follows carbocation stability: 3° > 2° > 1° 2-Methylpropan-2-ol is tertiary, propan-2-ol is secondary, and propan-1-ol is primary. Therefore: (A) > (B) > (C)

During reaction with thionyl chloride, the hydroxyl group of alcohol is replaced by chlorine. Since one group is substituted by another, the reaction is classified as a nucleophilic substitution reaction.

2-Methylbutane contains four different types of hydrogen positions. Chlorination at each unique position generates a different monochloro derivative. Therefore, four structural monochloro isomers are possible.

Free radical halogenation of alkanes is not preferred because it gives a complex mixture of products. Aryl iodination is reversible, so an oxidizing agent is required to remove HI and drive the reaction forward. Fluoroarenes are not generally prepared by direct electrophilic substitution because fluorine is highly reactive and difficult to control. Statement 4 is incorrect because HBr addition generally follows Markovnikov's rule, except in the presence of peroxides.

When bromine in CCl₄ is added to propene, bromine atoms add across the carbon-carbon double bond. Since the bromine atoms attach to adjacent carbon atoms, the product is a vicinal dibromide. For propene, the product is 1,2-dibromopropane.

Addition of HX to unsymmetrical alkenes follows Markovnikov's rule. Free radical halogenation of alkanes gives difficult-to-separate mixtures. Iodination of arenes is reversible and requires oxidizing agents like HNO₃ or HIO₄. Alkyl fluorides are prepared by the Swarts reaction.

In the Finkelstein reaction, alkyl chlorides or bromides react with sodium iodide in dry acetone to form alkyl iodides. Sodium chloride or sodium bromide is formed as a by-product and precipitates in dry acetone. This removal of product shifts equilibrium forward according to Le Chatelier's Principle.

Carbon-halogen bond lengths are extremely small distances. In NCERT tables, they are commonly expressed in picometres, written as pm. For example, C—F, C—Cl, C—Br and C—I bond lengths are given in pm.

Although fluorine is the most electronegative halogen, dipole moment depends on both electronegativity difference and bond length. The observed dipole moment order for methyl halides is: CH₃Cl > CH₃F > CH₃Br > CH₃I Thus, the decreasing order is: (A) > (B) > (C) > (D)

Fluorine is the most reactive halogen. Direct electrophilic fluorination of arenes is highly vigorous and difficult to control, often leading to unwanted side reactions. Therefore, fluoroarenes are generally not prepared by direct electrophilic substitution.

Benzenediazonium chloride reacts with cuprous chloride (Cu₂Cl₂/CuCl) in Sandmeyer reaction. The diazonium group (-N₂⁺Cl⁻) is replaced by chlorine, producing chlorobenzene.

The Swarts reaction is used to prepare alkyl fluorides from alkyl chlorides or alkyl bromides using metallic fluorides such as AgF, Hg₂F₂, CoF₂ or SbF₃. The reaction involves replacement of Cl or Br by F.

Carbon-halogen bond length depends on the atomic size of the halogen. As we move down the halogen group, atomic size increases: I > Br > Cl > F Therefore, bond lengths follow: C—I > C—Br > C—Cl > C—F Hence the decreasing order is: (A) > (B) > (C) > (D)

Organic halogen compounds are generally polar due to the electronegativity difference between carbon and halogen. Their intermolecular forces are stronger than those of parent hydrocarbons of comparable molecular mass. In isomeric haloalkanes, boiling point decreases with increase in branching because branching reduces surface area and weakens van der Waals forces. Statement 4 is incorrect because boiling points do not strictly increase with branching.

Haloalkanes dissolve in organic solvents because the new intermolecular attractions between haloalkane molecules and solvent molecules are nearly the same strength as the attractions being broken. This makes dissolution energetically favourable.

Para-isomers of dihalobenzenes have higher melting points because their symmetrical structure allows them to fit more efficiently into the crystal lattice. Better packing increases lattice stability, so more energy is required to melt the solid.

Pure alkyl halides are generally colourless. Bromides and iodides may develop colour when exposed to light due to decomposition. Many volatile halogen compounds have a sweet smell. Polychloro derivatives of hydrocarbons are usually heavier than water due to increased molecular mass.

The density of liquid halo compounds such as CHCl₃ is expressed in grams per millilitre, written as g/mL or g mL⁻¹. This unit indicates the mass of the liquid present in one millilitre of volume.