Which of the following statements are correct about alkylhalides:
(A) Alkylhalides are polar so they are soluble in water.
(B) RX on reaction with alc. KOH give alkenes
(C) RX on reaction with \(AgNO_2\) give \(RONO\)
(D) \(S_N1\) proceeds with inversion in configuration
(E) \(R-X\) have higher boiling point than parent alkanes
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (B), (E) only
The C–X bond of an alkyl halide is polar: carbon carries a partial positive charge and halogen a partial negative charge. This explains both its physical properties and its substitution and elimination reactions.
(A) Alkylhalides are polar so they are soluble in water — Incorrect. Although polar, haloalkanes are only very slightly soluble in water: the energy needed to break the hydrogen bonds between water molecules is not regained, because haloalkanes cannot form hydrogen bonds with water.
(B) RX on reaction with alc.KOH give alkenes — Correct. Alcoholic KOH removes HX (dehydrohalogenation, β-elimination):
\( \ce{CH3CH2Br + KOH(alc)} \xrightarrow{\Delta} \ce{CH2=CH2 + KBr + H2O} \)
(C) RX on reaction with \( \ce{AgNO2} \) give RONO — Incorrect. The nitrite ion is ambident. \( \ce{AgNO2} \) is mainly covalent, so attack occurs through nitrogen and the product is a nitroalkane, \( \ce{R-NO2} \); \( \ce{KNO2} \) (ionic) gives alkyl nitrites, R–O–N=O.
\( \ce{R-X + AgNO2 -> R-NO2 + AgX} \)
(D) SN1 proceeds with inversion in configuration — Incorrect. SN1 goes through a planar carbocation that can be attacked from either face, so an optically active halide gives a racemic mixture. Inversion is the mark of SN2.
(E) R−X have higher boiling point than parent alkanes — Correct. Greater polarity and higher molecular mass give stronger dipole–dipole and van der Waals forces, e.g. \( \ce{CH3Cl} \) (249 K) against \( \ce{CH4} \) (112 K).
NCERT (2026-27 edition):
Physical Properties – “… Due to greater polarity as well as higher molecular mass as compared to the parent hydrocarbon, the intermolecular forces of attraction (dipole-dipole and van der Waals) are stronger in the halogen derivatives. That is why the boiling points of chlorides, bromides and iodides are considerably higher than those of the hydrocarbons of comparable molecular mass. … The haloalkanes are very slightly soluble in water.”
Reactions of Haloalkanes – “… Similarly nitrite ion also represents an ambident nucleophile with two different points of linkage [–O—N=O]. The linkage through oxygen results in alkyl nitrites while through nitrogen atom, it leads to nitroalkanes. … In case of optically active alkyl halides, SN1 reactions are accompanied by racemisation.”