Structural Variations of Carbon Chains in Hydrocarbons

Topics

Various Types of Hydrocarbons
Straight-Chain Hydrocarbons
Branched-Chain Hydrocarbons
Cyclic Hydrocarbons (Rings of Carbon Atoms)

Various Types of Hydrocarbons

Category	Saturated Hydrocarbons	Unsaturated Hydrocarbons
Straight-chain hydrocarbons	\[\begin{array}{cc} \ce{\phantom{}H\phantom{..}H\phantom{..}H}\\ \phantom{}\|\phantom{...}\|\phantom{...}\|\\ \ce{H-C-C-C-H}\\ \phantom{}\|\phantom{...}\|\phantom{...}\|\\ \ce{\phantom{}H\phantom{..}H\phantom{..}H}\\ \end{array}\] Propane (C₃H₈)	\[\begin{array}{cc} \phantom{....}\ce{H}\phantom{..}\ce{H}\phantom{..}\ce{H}\phantom{..}\\ \phantom{...}\|\phantom{...}\|\phantom{...}\|\phantom{.}\\ \phantom{.}\ce{H-C-C=C}\phantom{..}\\ \phantom{.....}\|\phantom{.......}\|\phantom{...}\\ \phantom{...}\ce{H}\phantom{......}\ce{H}\phantom{.} \end{array}\] Propene (C₃H₆) \[\begin{array}{cc} \ce{\phantom{.......}H}\\ \phantom{.......}\|\\ \ce{H-C≡C-C-H}\\ \phantom{.......}\|\\ \ce{\phantom{.......}H}\\ \end{array}\] Propyne (C₃H₄)
Branched-chain hydrocarbons	\[\begin{array}{cc} \phantom{}\ce{H}\phantom{..}\ce{H}\phantom{..}\ce{H}\phantom{}\\ \phantom{}\|\phantom{...}\|\phantom{...}\|\phantom{}\\ \phantom{}\ce{H-C-C-C-H}\\ \phantom{}\|\phantom{...}\|\phantom{...}\|\phantom{}\\ \phantom{}\ce{H}\phantom{..}\ce{\|}\phantom{..}\ce{H}\phantom{}\\ \phantom{}\ce{H-C-H}\\ \phantom{}\|\\ \phantom{}\ce{H} \end{array}\] Isobutane (C₄H₁₀)	Isobutylene (C₄H₈)
Cyclic hydrocarbons	Cyclohexane (C₆H₁₂) Cyclopentane (C₅H₁₀)	Cyclohexene (C₆H₁₀) Benzene (C₆H₆)

Straight-Chain Hydrocarbons

A straight-chain hydrocarbon consists of carbon atoms joined in a continuous chain without branching. These belong to the alkane family, which contains only single bonds (C–C).

Straight Chain of Carbon Atoms	Structural Formula	Molecular Formula	Name
C	CH₄	CH₄	Methane
C–C	H₃C—CH₃	C₂H₆	Ethane
C–C–C	H₃C—CH₂—CH₃	C₃H₈	Propane
C–C–C–C	H₃C—(CH₂)₂—CH₃	C₄H₁₀	Butane
C–C–C–C–C	H₃C—(CH₂)₃—CH₃	C₅H₁₂	Pentane
C–C–C–C–C–C	H₃C—(CH₂)₄—CH₃	C₆H₁₄	Hexane
C–C–C–C–C–C–C	H₃C—(CH₂)₅—CH₃	C₇H₁₆	Heptane
C–C–C–C–C–C–C–C	H₃C—(CH₂)₆—CH₃	C₈H₁₈	Octane
C–C–C–C–C–C–C–C–C	H₃C—(CH₂)₇—CH₃	C₉H₂₀	Nonane
C–C–C–C–C–C–C–C–C–C	H₃C—(CH₂)₈—CH₃	C₁₀H₂₂	Decane

These hydrocarbons are saturated (alkanes) because they contain only single bonds between carbon atoms.

Branched-Chain Hydrocarbons

When a carbon chain has side branches, it forms a branched hydrocarbon. These branches are called alkyl groups, and their presence leads to structural isomerism (same molecular formula, different structure).

Example: Butane (C₄H₁₀) – Two Isomers

Isomer Type	Structural Formula	Name
Straight Chain	H₃C—CH₂—CH₂—CH₃	n-Butane
Branched Chain	H₃C—CH—CH₃	Iso-butane

This phenomenon is called structural isomerism because the same molecular formula represents different compounds with distinct physical and chemical properties.

Cyclic Hydrocarbons (Rings of Carbon Atoms)

Cyclic hydrocarbons have carbon atoms arranged in a closed-ring structure. They can be:

Saturated (Cycloalkanes): Only single bonds between carbon atoms.
Unsaturated (Cycloalkenes & Cycloalkynes): contain double or triple bonds within the ring.

Cyclic Hydrocarbon	Molecular Formula	Structural Formula
Cyclopropane	C₃H₆
Cyclobutane	C₄H₈
Cyclopentane	C₅H₁₀
Cyclohexane	C₆H₁₂
Cyclohexene	C₆H₁₀
Benzene (Aromatic Hydrocarbon)	C₆H₆