Q.34. - Organic Chemistry

Question

Question: Hydrocarbon A possesses a significant dipole, even though it is composed of only C-C and C-H bonds. Explain why the dipole arises and use resonance structures to illustrate the direction of the dipole. Which ring is more electron rich?

Step-by-Step Solution

Answer

Answer

This molecule also possesses a net dipole moment. The seven membered ring is electron deficient and the five-membered ring is electron rich in nature as shown in the structure below:

Resonating structures

Step 1: Aromatic compounds

The compounds which are cyclic, are planar, and have a total of $\left(4n+2\right)\mathrm{\pi }$ electrons are aromatic in nature. The aromatic compounds are stable than the acyclic compounds with similar number of $\mathbf{\pi }$ electrons.

The most common aromatic compound is benzene.

Step 2: The illustration of the dipole in the given molecule.

For the given compound, the following resonating structures are possible:

Resonating structures

From the above resonating structures, it is clear that there is a negative charge on the five membered ring. It also shows that there is a positive charge on the seven-membered ring. 

The above resonating structure also makes it clear that each ring has a total of $6\mathrm{\pi }$ electrons which makes it aromatic in nature. This molecule also possesses a net dipole moment. The seven membered ring is electron deficient and the five-membered ring is electron rich in nature.