Choose the incorrect statements from the following:
(A) The dipole moment of cyclohexyl chloride is smaller than chlorobenzene.
(B) Alkyl halides are immiscible with water.
(C) The dipole moment of methyl chloride is higher than that of methyl fluoride.
(D) Chloroform renders aerial oxidation in the presence of oxygen
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B) and (D) only
The dipole moment of a molecule is the product of the charge separation and the distance between the charges (\( \mu = q \times d \)). In haloalkanes the C–X bond is polar because the halogen is more electronegative than carbon. Each statement is judged below; the question asks for the incorrect ones.
(A) The dipole moment of cyclohexyl chloride is smaller than chlorobenzene. — Incorrect. In chlorobenzene the C–Cl carbon is sp2 hybridised and the lone pair of chlorine is in resonance with the ring, which gives the bond partial double bond character and less polarity. So chlorobenzene (about 1.7 D) has the smaller dipole moment and cyclohexyl chloride (about 2.2 D) the larger.
(B) Alkyl halides are immiscible with water. — Incorrect. Haloalkanes are polar and are slightly soluble in water, not wholly immiscible. They dissolve only a little because the energy released in their weak attractions with water is less than that needed to break the hydrogen bonds between water molecules.
(C) The dipole moment of methyl chloride is higher than that of methyl fluoride. — Correct. \( \ce{CH3Cl} \) has 1.860 D and \( \ce{CH3F} \) 1.847 D. Fluorine is more electronegative, but the C–Cl bond is much longer, and the larger distance d outweighs the smaller charge separation.
(D) Chloroform renders aerial oxidation in the presence of oxygen — Incorrect. Chloroform does not cause oxidation; it is itself slowly oxidised by air, and only in the presence of light, to the poisonous gas phosgene:
\( \displaystyle \ce{2CHCl3 + O2} \xrightarrow{\text{light}} \ce{2COCl2 + 2HCl} \)
This is why chloroform is stored in closed, dark coloured bottles filled to the brim.