Chemistry · General Principles Of Organic Chemistry · NEET
Cyclohexane is alicyclic, and alicyclic compounds are grouped under aliphatic in classification. It is a ring, but it does NOT have delocalised pi electrons in a flat ring, so it is not aromatic. Simple rule: cyclohexane behaves like an open-chain alkane bent into a ring, so it stays on the aliphatic side.
Both are rings. Alicyclic rings (like cyclopropane, cyclohexane) act like normal aliphatic compounds and can be saturated. Aromatic rings (like benzene) are flat, have a closed loop of delocalised pi electrons, are extra stable, and give substitution rather than addition. So the ring alone does not decide it; the delocalised pi electron loop does.
No. This is the most common NEET mistake. A compound is aromatic only if it is cyclic, planar, has a continuous ring of overlapping p-orbitals, and follows Huckel's rule (4n+2 pi electrons). A ring that fails any of these, like cyclohexane or cyclohexene, is alicyclic, not aromatic.
In the NCERT scheme, compounds first split into acyclic (open-chain) and cyclic. Cyclic then splits into alicyclic (aliphatic-type rings), aromatic, and heterocyclic. So alicyclic is a type of cyclic compound, and in behaviour it is treated as aliphatic. Aliphatic in the broad sense covers open chains plus alicyclic rings, and stands opposite to aromatic.
Benzene is the parent aromatic compound. It is a flat six-carbon ring with 6 delocalised pi electrons (4n+2 with n=1), which makes it aromatic and unusually stable. It is never classified as aliphatic even though it is a hydrocarbon.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
If the compound has a benzene-type flat ring with delocalised pi electrons following 4n+2, it is aromatic. Everything else (open chains and normal rings like cyclohexane) is aliphatic/alicyclic.
They can be either. Cyclohexane is a saturated alicyclic compound; cyclohexene and cyclohexyne are unsaturated alicyclic compounds. Being unsaturated does not make them aromatic.
No. Cyclohexene has only one double bond, so its pi electrons are not delocalised around the whole ring and it fails Huckel's rule. It is an unsaturated alicyclic compound.
Not always. Benzenoid aromatics contain a benzene ring, but non-benzenoid aromatics (like tropylium cation) and heterocyclic aromatics (like pyridine, furan) are also aromatic. All of them still satisfy the aromaticity conditions.
Addition would break the stable delocalised pi ring and destroy aromaticity. Substitution keeps the ring intact, so aromatic compounds like benzene undergo electrophilic substitution instead of addition.
