NEET UG 2008 — Chemistry Organic Chemistry

Key Idea : As the number of lone pair of electrons increases, bond angle decreases. $\mathrm{NO}_2^{+}$NO2+​ion is isoelectronic with $\mathrm{CO}_2$CO2​ molecule. It is a linear ion and its central atom $\left(\mathrm{N}^{+}\right)$(N+) undergoes $s p$sp-hybridisation, hence bond angle is $180^{\circ}$180∘. In $\mathrm{NO}_2^{-}$NO2−​ion, $\mathrm{N}$N-atom undergoes $s p^2$sp2 hybridisation. The angle between hybrid orbital should be $120^{\circ}$120∘ but one lone pair of electrons is lying on $\mathrm{N}$N-atom, hence bond angle decreases to $115^{\circ}$115∘. In $\mathrm{NO}_2$NO2​ molecule, $\mathrm{N}$N-atom has one unpaired electron in $s p^2$sp2-hybrid orbital. The bond angle should be $120^{\circ}$120∘ but actually it is $132^{\circ}$132∘. It may be due to one unpaired electron in $s p^2$sp2-hybrid orbital. Therefore, the increasing order of bond angles is : $$\underset{\left(115^{\circ}\right)}{\mathrm{NO}_2^{-}} < \underset{\left(132^{\circ}\right)}{\mathrm{NO}_2} < \underset{\left(180^{\circ}\right)}{\mathrm{NO}_{+}^{+}}$$(115∘)NO2−​​<(132∘)NO2​​<(180∘)NO++​​