Q11.57CP - Chemistry: Molecular Nature Of Matter And Change

Question

The compound 2,6-dimethyl pyrazine (below) gives chocolate its odor and is used in flavourings.

1. Which atomic orbitals mix to form the hybrid orbitals $\mathbf{N}$  ?
2. In what type of hybrid orbital do the lone pairs  $\mathbf{N}$   reside?
3. Is  $\mathbf{C}$ in  ${\mathbf{CH}}_{\mathbf{3}}$  hybridized the same as any $\mathbf{C}$  in the ring? Explain. 

Step-by-Step Solution

Answer

Hybridization provides a hybrid state for the overlapping of electrons to maximize stability.

 

The answer for

a) one  $\mathbf{s}$ and two $\mathbf{p}$  atomic orbitals.

b)  ${\mathbf{sp}}^{\mathbf{2}}$ orbital

c) No

Step 1: Definition

The atomic orbitals fuse to form new orbitals with completely different energies, shapes, and so on.

 

Atomic orbitals are mixed together to create hybrid orbitals. The total number of hybrid orbitals is equal to the no. of bond pair +no. of lone pair on the central atom.

 

Step 2: Atomic orbital of N

In the benzene ring, nitrogen is surrounded by two bond pairs and one lone pair. the one  and two $\mathbf{p}$  atomic orbitals mix to form a hybrid orbital  $\mathbf{N}$. Hence, its hybridization is  ${\mathbf{sp}}^{\mathbf{2}}$ .

 

Step 3: For lone pair of N

In the vacant ${\mathbf{sp}}^{\mathbf{2}}$  orbital residing on the $\mathbf{N}$  atom, the lone pairs of nitrogen reside.

In the hybridized  ${\mathbf{sp}}^{\mathbf{2}}$ orbitals the lone pair is held because nitrogen has a pi bond (the unhybridized $\mathbf{p}$ orbital) which must contain a pair of electrons used to form the double bond.

 

Step 4: Hybridization of C in CH 3

No, the hybridization of carbon ${\mathbf{CH}}_{\mathbf{3}}$  is ${\mathbf{sp}}^{\mathbf{3}}$  as it is surrounded by 4 bond pairs (3 $\mathbf{H}$ atoms+1 $\mathbf{C}$ atom) whereas other carbon is ${\mathbf{sp}}^{\mathbf{2}}$  as it is surrounded by 2 bond pairs (2$\mathbf{C}$ atoms) and one lone pair.