CHEMISTRY - OBJECTIVE - 3

9. Benzamide on treatment with POCL3 gives 

(a) aniline                     (b) benzonitrile

(c) chlorobenzene          (d) benzyl amine

answer (b)

Answer explanation :Benzamide (C6H5CONH2) on treatment with POCL3 (POCL3 is Phosphorous oxy chloride ) gives C6H5-C≡N (triple bond).

This is called Benzonitrile. nitrile has triple bond for amino group

Nitrogen has electronic configuration 2,2,3 (atomic number of nitrogen is 7). outer 'p' orbital has 3 electrons (1s2,2s2,2p3)

Nitrogen has multiple energy level electrons since it is an inert gas .Inert gas means slow moving electrons inside atoms.So, 'p' orbital has three electrons, since nucleus attracts towards inside more, the inner layer electrons (in s layer) in the valence covalent bond in the case of Nitrogen and Hydrogen .

Hydrogen has 1 atomic number and 1 electron mates with oxygen to form water H2O. Oxygen has atomic number 8,it has 8 electrons .1s,2s,2p levels has 2,2,4 electrons respectively. So, 4 electrons shall part from oxygen atom. Thus, four valence electrons are required for oxide formation for any inert gas .

Carbon has atomic number 6(1S2,2S2,2P2). CN has one single carbon mating with three Nitrogen atoms    ( triple bond). 

 Nitrogen has 3 electrons in the outer layer, out of which 1 mates with carbon .Hence C≡N molecule has Nitrogen atom in which 1 electron is shared with carbon, and 2 free electrons remain free for each Nitrogen atom.So CH3-CH2-C≡N has 6 electrons free for three Nitrogen atoms.