Question -
Answer -
(ii) alkyl halides, though polar, are immiscible with water?
(iii) Grignard reagents should be prepared under anhydrous conditions?
Answer
In chlorobenzene, the Cl-atom is linked toa sp2 hybridized carbon atom. In cyclohexyl chloride, theCl-atom is linked to a sp3 hybridized carbonatom. Now, sp2 hybridized carbon has more s-character than sp3 hybridizedcarbon atom. Therefore, the former is more electronegative than the latter.Therefore, the density of electrons of C−Cl bond near the Cl-atom is less in chlorobenzenethan in cydohexyl chloride.
Moreover, the −R effect of the benzene ring ofchlorobenzene decreases the electron density of the C−Cl bond near the Cl-atom.As a result, the polarity of the C−Cl bond in chlorobenzene decreases. Hence,the dipole moment of chlorobenzene is lower than that of cyclohexyl chloride.
(ii) To be miscible with water, the solute-water force ofattraction must be stronger than the solute-solute and water-water forces ofattraction. Alkyl halides are polar molecules and so held together bydipole-dipole interactions. Similarly, strong H-bonds exist between the watermolecules. The new force of attraction between the alkyl halides and watermolecules is weaker than the alkyl halide-alkyl halide and water-water forcesof attraction. Hence, alkyl halides (though polar) are immiscible with water.
(iii) Grignard reagents are very reactive. In the presence ofmoisture, they react to give alkanes.
Therefore, Grignard reagents should be prepared underanhydrous conditions.