Q.61. - Organic Chemistry

Question

Question: Zolpidem (trade name Ambien) promotes the rapid onset of sleep, making it a widely prescribed drug for treating insomnia.

a. In what type of orbital does the lone pair on each N atom in the heterocycle reside? 

b. Explain why the bicyclic ring system that contains both N atoms is aromatic. 

c. Draw all reasonable resonance structures for the bicyclic ring system.

Step-by-Step Solution

Answer

Answer

a.

b. The compound is aromatic due to the presence of lone pair of electrons in conjugation.   

c. 

Step 1: Aromatic compound

The “Huckle rule” determines whether the compound is aromatic or not. If the compounds obey the $\mathbf{4}\mathit{n}\mathbf{+}\mathbf{2}$ rule, where $\mathit{n}\mathbf{=}\mathbf{0}\mathbf{,}\mathbf{1}\mathbf{,}\mathbf{2}\mathbf{,}\mathbf{3}\mathbf{,}\mathbf{4}\mathbf{.}\mathbf{.}\mathbf{.}\mathbf{.}\mathbf{.}\mathbf{.}\mathbf{.}\mathbf{.}\mathbf{.}$ , then they are aromatic.

Step 2: Heteroaromatic compound

The heteroaromatic bicyclic compound which contains nitrogen atoms is aromatic. The heteroatoms such as nitrogen, oxygen, halogen contain lone pair of electrons that participate in the delocalization. Therefore, the compounds are aromatic.  

Step 3: Explanation

a.

 

The double bonded nitrogen has sp2  bonding. Therefore, the lone pair exists in the sp2  . The single-bonded nitrogen has sp3  bonding. Therefore, the lone pair exists in the  sp3 .

Hybridization of nitrogen

 

b.

 

The bicyclic ring containing N is aromatic due to the lone pair of electrons on the nitrogen atom which undergoes delocalization.  

Aromatic system

 

c.

 

The resonating structure of the given bicyclic hetero-compound is due to the delocalization of electrons.

Resonating structures