Question

For the structure below, determine the total number of π  electrons and the number of π  electrons delocalized in the ring. Indicate whether the compound is aromatic, nonaromatic, or antiaromatic. Assume the structure is planar.

Answer 1

General guidance

Concepts and reason

The concept used in this problem is of aromaticity. The compounds which contain $4n + 2$ delocalized $\\pi$electrons are aromatic where, n is any whole number. Anti-aromatic compounds contain $4n$ delocalized $\\pi$electrons.

Fundamentals

One $\\pi$ bond contains two $\\pi$electrons. A double bond contains one sigma bond and one $\\pi$ bond. A triple bond contains one sigma bond and two $\\pi$ bonds.

Step-by-step

Step 1 of 3

The total number of $\\pi$ bonds is 8. Each bond contains two electrons. So, the number of $\\pi$ electrons are 16.

Total number of $\\pi$ electrons are 16.

Explanation | Common mistakes | Hint for next step

There is one triple bond and six double bonds in the structure.

As a triple bond contains two $\\pi$ bonds and double bond contain one $\\pi$ bond. So, there are total 8 $\\pi$ bonds and 19 $\\pi$ electrons.

Step 2 of 3

Out of two $\\pi$ bonds of one alkyne in structure, only electrons of one $\\pi$bond participate in delocalization. The delocalization is shown as follows:

Total 7 $\\pi$ bonds participate in delocalization out of total 8. So, 14 $\\pi$ electrons delocalize in the structure.

Number of $\\pi$ electrons delocalized in the ring are 14.

Explanation

There are total 8 $\\pi$ bonds or 16 $\\pi$ electrons out of which one $\\pi$ bond of triple bond is not participating in delocalization.

Step 3 of 3

Total 7 $\\pi$ bonds participate in delocalization out of total 8. So, 14 $\\pi$ electrons delocalize in the structure.

When n is 3, $4n + 2$ would be 14. So, the compound is aromatic.

The compound is aromatic.

Explanation

There are total 8 $\\pi$ bonds or 16 $\\pi$ electrons out of which one $\\pi$ bond of triple bond is not participating in delocalization. So, this one $\\pi$ bond is not considered in finding aromaticity of the compound.

Answer

Total number of $\\pi$ electrons are 16.

Number of $\\pi$ electrons delocalized in the ring are 14.

The compound is aromatic.

Answer only

Total number of $\\pi$ electrons are 16.

Number of $\\pi$ electrons delocalized in the ring are 14.

The compound is aromatic.