Question

Why is Cyclohexane considered "Cyclic" and Benzen "aromatic"? Use the word resonance in your answer.

Answer 1

Cyclohexane is a saturated, cyclic hydrocarbon. The molecule is formed of only sigma bonds(bonds formed by head on overlap of electrons). Hence, there is no "delocalisation" or resonance of electrons which is one of the necessary criteria for a molecule to be aromatic. Also, aromatic molecules are planar in nature and the most stable form of cyclohexane is the chair form which is non-planar in nature. Hence, cyclohexane is rightfully called "cyclic" and not "aromatic"

Benzene is a cyclic compound but it also satisfies all the criteria for being aromatic:

1) Compound is planar

2)Compound is cyclic

3)There is delocalisation or resonance of electrons throughout the ring

4) The number of delocalised or resonating pi electrons is equal to (4n+2), n=0,1,2,....[This is known as Huckel's rule]

Hence, benzene is stabilised by resonance of the 4n+2 pi electrons.

This makes benzene "aromatic" and cyclohexane "cyclic"

exctic form of cyckhexare Chair form of cyclohexane J & Delordised 20 Telertrous O Horough lesandiner