Please explain each case.
Please explain each case.​ Using Huckel's rule predict, how many of the following are aromatic hydrocarbons ?

Dear Student,

The energy level and Huckel rule of 4n+2 are used in determining the aromaticity, in simple bonding results in aromaticity and anti-bonding leads to non-aromatic character. Based on Huckel rule the molecule must possess below characteristics for the aromatic property,

1. The cyclic compound must contain uninterrupted "pi" electron system and hence comprised of cyclic - conjugated double bonds where p orbital in each ring is perpendicular to the ring plane.

2. The rings in aromatic compounds are planar, where optimal overlapping are allowed for high stability of the molecule

3. The number of "pi" electron must obey the thumb rule of 4n+2 as per Huckel's rule

The above three properties have to be fulfilled by the given molecules for exhibiting aromatic property if any one fails will lead to anti-aromaticity.

For instance in molecule #1 cyclobutadiene  obeys rule 1 and 2 but fails to meet rule 3 leads to 4pi electrons hence the molecule is antiaromatic in nature.

molecule #2 anti-aromatic as least stable by the lone pair presence

molecule #3 aromatic in nature as it obeys rule 1,2 and 3

molecule #4 aromatic in nature as it obeys rule 1,2 and 3

molecule #5 aromatic in nature as it obeys rule 1,2 and 3

molecule #6 anti-aromatic as it fails to meet rule 1

molecule #7 anti-aromatic as it fails to meet rule 1

molecule #8 aromatic in nature as it obeys rule 1,2 and 3

Regards.

 

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