Q15-11P - Organic Chemistry (Mcmurry)

Question

Azulene, a beautiful blue hydrocarbon, is an isomer of naphthalene. Is azulene aromatic? Draw a second resonance form of azulene in addition to that shown.

Step-by-Step Solution

Answer

Azulene is aromatic due to 10 π-electron is present.

Resonating structure of azulene:

Step 1: 4n+2 rule

It is the rule to check the aromaticity of the compound by knowing the number of delocalized electrons like in cyclodecapenatnene has 5 double bonds which mean the then electron and n=2 so that the system is aromatic because n is a whole number.

It is known as Huckel’s rule.

Step 2: Aromaticity of azulene

As the structure of azulene is visible that it has 5 double bonds that the 10 electrons so by Huckel’s rule that4n+2 the n=2 so the molecule is aromatic.

Step 3: Resonating structure

These are the structure of the Lewis acid in which the delocalization of the pi-electron occurs in the ring and make the bond length of the C-C bond equal.

Delocalisation occurs due to the partial charges and fractional bonds in it.  

Step 4: Resonating structure of azulene

The structure of azulene has 5 double bonds so one of its resonating structures is formed in the carbon double replaces by single and single bond replaced by a double bond as shown: