Chemistry · Hydrocarbons · NEET
A hydrocarbon contains ONLY carbon and hydrogen atoms. Nothing else. If a molecule has oxygen (like alcohol CH3OH), nitrogen (like an amine), or a halogen (like CH3Cl), it is NOT a hydrocarbon. This is the first thing NEET checks: methane (CH4), ethene (C2H4) and benzene (C6H6) are hydrocarbons; ethanol (C2H5OH) is not because of the oxygen.
Aliphatic hydrocarbons have open carbon chains or plain rings (like alkanes, alkenes, alkynes). Aromatic hydrocarbons contain a special benzene ring with delocalised electrons that make it extra stable. Easy check: if the structure has a benzene ring (C6H6 based), it is aromatic; otherwise it is aliphatic. Aromatic compounds mostly do substitution, not addition.
Saturated means every carbon-carbon bond is a single bond, so carbon holds the maximum hydrogen it can. These are the alkanes. Unsaturated means there is at least one C=C double bond (alkenes) or C≡C triple bond (alkynes), so the molecule holds fewer hydrogens. Unsaturated hydrocarbons are more reactive because the double or triple bond can be broken open by addition reactions.
Count the bond between carbons. Only single bonds = alkane (name ends in -ane, formula CnH2n+2). One double bond = alkene (ends in -ene, formula CnH2n). One triple bond = alkyne (ends in -yne, formula CnH2n-2). So C2H6 is an alkane, C2H4 is an alkene, C2H2 is an alkyne. The name ending tells you the bond type.
Benzene is AROMATIC, not aliphatic, even though it is a ring. Not every ring is aliphatic. Benzene (C6H6) has a special ring where six electrons are shared equally around all six carbons (delocalised). This makes it very stable and it prefers substitution reactions. A simple ring like cyclohexane, with no such delocalisation, is aliphatic (called alicyclic).
Each extra bond between two carbons uses up bonding positions that hydrogen could have taken. In ethane (C2H6) both carbons are joined by one bond, leaving room for 6 H. Make it a double bond (ethene C2H4) and you lose 2 H. Make it a triple bond (ethyne C2H2) and you lose 2 more H. So more bonds between carbons means fewer hydrogens. That is why they are called 'unsaturated'.
The compound that will react most readily with gaseous bromine has the formula:
The pair of electrons in the given carbanion, CH3-C≡C(-), is present in which of the following orbitals?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes. By definition a hydrocarbon has only C and H atoms. Any other element (O, N, S, halogen) means it is not a hydrocarbon.
Alkanes (single bonds only), alkenes (one C=C double bond), alkynes (one C≡C triple bond), and aromatic hydrocarbons (benzene-ring compounds like benzene and toluene).
Alkenes and alkynes are unsaturated because they contain double or triple carbon-carbon bonds. Alkanes are saturated with only single bonds.
Benzene is technically unsaturated (it has ring double bonds) but it is classed separately as aromatic because its delocalised electrons make it unusually stable and it mostly does substitution, not addition.
Classification decides which reactions a compound does. Knowing saturated vs unsaturated and aliphatic vs aromatic lets you predict products in bromine tests, addition, and substitution questions that appear every year.
