Haloalkanes and Haloarenes MCQs

Ans. (A) Cl^- <Br ^- < I ^-

Explanation: The elements placed in the downward direction of the periodic table tend to possess larger atomic sizes. In such groups, the electrons are not closely bound to the nucleus, so they can easily lose them to form new C-X bonds. Therefore, the nucleophilicity increases from Cl^- <Br^- < I^- .

Ans. (D) Nitric acid over chloroform.

Explanation: Chloropicrin is a product obtained through the reaction between nitric acid and chloroform. In this reaction step, upon treating the chloroform with concentrated nitric acid, the hydrogen group present in the chloroform is replaced by the nitro group from the nitric acid giving rise to the product as mentioned earlier.

Ans. (B) Partial racemization.

Explanation: Racemization is a conversion process associated with the SN₁ reaction of alkyl halides. It is so because the SN₁ reaction of optically active alkyl halide exhibits nucleophilic attack from two sides to form bonds with the trigonal planar structure. Therefore, this reaction results in partial racemization conversion.

Ans. (D) CH₃F.

Explanation: Since the halogen atom is highly electronegative in comparison to the carbon atom, the electrostatic bond between fluorine and carbon is so strong that it pulls the electron pair towards itself instead of the carbon atom. Therefore, the C-F bond possesses the highest bond strength.

Ans. (A) Carbonyl chloride.

Explanation: Carbonyl chloride or COCl₂ is also identified as phosgene as its common name. It is a transparent, unpleasant odor carrying poisonous gas known to exhibit severe irritation to the eyes, throat, and rest of the respiratory system upon exposure. It has a broad spectrum of applications in the plastic and pesticide industries.

Ans. (D) An oxidative process.

Explanation: Halogenation of alkanes is an oxidative process since ultraviolet light or heat (energy sources to promote homolytic cleavage of halogen groups) are used to collide with alkane, resulting in haloalkanes or alkyl halides.

Ans. (D) Raschig process

Explanation: The Raschig-Hooker is a chemical process used by industries to produce phenols. It is also used for the commercial preparation of chlorobenzene. A copper oxide catalyst is used in this process to treat benzene vapours in the presence of hydrogen chloride gas and oxygen at a temperature of 250 degrees Celsius.

Ans. (B) p-dichlorobenzene

Explanation: A para isomer of a given chemical molecule has higher symmetry, which allows the molecule to remain within a crystal better than an ortho or meta isomer. Therefore, the p-dichlorobenzene or the para isomers possess a higher melting point and low solubility than their ortho (o) or meta (m) counterparts.

Ans. (B) CH₃Cl

Explanation: The halogen groups possess high electronegativity and exhibit intense dipole moments. In comparison with bromine and chlorine, fluorine has the maximum electronegativity. The dipole moment of CH₃F is restricted by the smaller distance between the carbon and fluorine groups. Therefore, CH₃Cl poses the highest dipole moment.

Ans. (D) Ethylene glycol.

Explanation: The ethylene dichloride is synthesized by the addition of hydrochloric acid to ethylene glycol. In this reaction step, the CH₂OH⋅CH₂OH (ethylene glycol), when mixed with 2HCl (hydrochloric acid), produces C₂H₄Cl₂ (ethylene dichloride) and 2H₂O (water). The chlorine group replaces the hydroxyl group in ethylene glycol, an example of a displacement reaction.

Ans. (B) Sodium iodide stays soluble in methanol, while sodium chloride and sodium bromide stay insoluble in methanol.

Explanation: Conant Finkelstein reaction is understood to be an SN₂ reaction process wherein the reaction equilibrium is maintained by one nucleophile group (halogen atom) replacing the other from the leaving group. Alkyl chloride or bromide is converted into alkyl iodide by adding sodium iodide to methanol in this reaction.

Ans. (A) Anhydrous ZnCl₂ 

Explanation: Anhydrous ZnCl₂ is a catalyst that supports nucleophilic substitution reaction, unlike an anhydrous AlCl₃, which helps the electrophilic substitution reaction. When H⁺ ions and Cl^- ions are displaced from anhydrous ZnCl₂, Cl^- ions can attack the OH ^- group of the alcohol. The reaction is favored by the displacement of H⁺ ions and Cl^- ions.

Ans. (B) Isopropyl chloride

Explanation: An alkyl halide is identified as a secondary halide if the compound has a functional group attached to the second carbon position. Unlike the other compounds stated in the option, isopropyl chloride has a Cl^- functional group attached to its secondary carbon atom. Therefore, it is considered a secondary halide.

Ans. (A) Neohexyl chloride

Explanation: If the compound's primary carbon carries a functional group, it is considered a primary halide. In neohexyl chloride, the compound has a Cl^- functional group attached to its primary carbon atom, unlike the other compounds stated in the options. Therefore, it is considered a primary halide.

Ans. (B) Two

Explanation: Structural isomers are molecules whose atoms are rearranged in a new pattern within the molecular formula. The compound with the molecular formula C₃H₇Cl is known to be n-propyl chloride. This compound can have two structural isomers, namely 1-chloropropane and 2-chloropropane.

Ans. (A) gem-dihalide.

Explanation: The alkylene dihalide, based on the position of the halogen groups on the carbon atom these compounds further divided into gem-halides and vic-halides. The former group possesses two halogen groups on the same carbon atom, while the latter possesses two halogen groups on the adjacent carbon atom.

Ans. (C) RI > RBr > RCl > RF .

Explanation: The boiling point for the given set of alkyl halides depends on the halogen group's atomic mass associated with the hydrocarbon structure (iodine has a high atomic mass, while fluorine has the lowest atomic mass). The boiling point for alkyl halide increases in proportion to the increasing atomic mass of the halogen atom and decreases with decreasing atomic mass.

Ans. (C) 2-Chloro-2-methylpropane

Explanation: The IUPAC name of the (CH₃)₃CCl is 2-Chloro-2-methylpropane. The longest carbon chain comprises three carbon atoms, hence, considered propane. Both the halogen groups chloride and methyl groups are bound to the second carbon atom with naming preference given based on the alphabetical order, representing 2-Chloro-2-methylpropane.