Hydrocarbons: classification, nomenclature and exercises

Hydrocarbons are compounds formed only by carbon and hydrogen, with a general formula: C_xH_y.

It is an extensive amount of substances, the best known of which are constituents of oil and natural gas.

The backbone of a hydrocarbon is made up of carbon and, in turn, the hydrogen atoms bond through a covalent bond.

They are widely used in the chemical industry, being essential in the production of petroleum derivatives: fuels, polymers, paraffins, among others.

Properties of hydrocarbons

molecular interaction	They are practically non-polar compounds and their molecules are joined by an induced dipole.
Melting and boiling point	They are low compared to polar compounds.
aggregation states	Gaseous: composed of 1 to 4 carbons. Liquid: composed of 5 to 17 carbons. Solid: compounds with more than 17 carbons.
Density	They have a lower density than water.
Solubility	They are insoluble in water and soluble in non-polar substances.
Reactivity	Low: open-chain compounds and single bonds. Medium: open-chain compounds and double bonds. High: cyclic compounds of 3 to 5 carbons.

Classification of hydrocarbons

As for the form of the main carbon chain, hydrocarbons are classified into:

aliphatic hydrocarbons

Formed by open or acyclic carbon chains, which have terminal carbons.

• alkanes
• alkenes
• Alkynes
• Alkadienes

Example:

2,2,4-trimethylpentane

See too: carbon chains

Cyclic hydrocarbons

Formed by closed or cyclic carbon chains which do not have terminal carbons.

• Cyclans
• Cycles
• cyclists
• Aromatics

Examples:

See too: benzene

As for the bonds of carbon chains, whether single, double or triple:

Saturated hydrocarbons

Compounds are formed by single bonds between carbon and hydrogen atoms.

• alkanes
• Cyclans

Example:

Methylcyclopentane

unsaturated hydrocarbons

The compounds formed have double or triple bonds between carbon and hydrogen atoms.

• alkenes
• Alkynes
• Alkadienes
• Cycles
• cyclists
• Aromatics

1-pentene

Also read about:

• Chemical bonds
• Organic chemistry
• Organic Functions

Nomenclature

The nomenclature of hydrocarbons is defined by the following terms:

PREFIX	INTERMEDIARY	SUFFIX
Indicates the number of carbons present in the chain.	Type of link found in string.	Identification of the functional group.

PREFIX	INTERMEDIARY	SUFFIX
1C	MET	Single link only	AN	O
2C	ET
3C	PROP	a double bond	EN
4C	BUT
5C	PENT	two double bonds	DIEN
6C	HEX
7C	HEPT	A triple bond	IN
8C	OCT
9C	NON	Two triple links	DIIN
10C	DEC

Examples

Follow how hydrocarbon names are formed:

Ethane

• Prefix: ET, which corresponds to 2 carbons.
• Intermediary: AN, which corresponds to simple links.
• Suffix: O, which corresponds to the hydrocarbon function.

Look at the other examples:

	Propane
	Ethene
	Etino
	propadiene

In some cases it is necessary to indicate the position of the double or triple bond. Numbering must start from the closest end of that link.

	1,3-butadiene
	1-butyne

Learn more at:

• Butane
• Methane

Types of Hydrocarbons

Check out the main types of hydrocarbons, their characteristics and the compounds used:

alkanes

They are open chain hydrocarbons with single bonds between carbon and hydrogen atoms, whose general formula is Ç_noH_2n+2.

Alkanes Characteristics

• They are also called paraffins or paraffins.
• They are found in nature in natural gas and oil.
• Are used as fuels: cooking gas, gasoline, diesel oil, etc.

Examples of alkanes

alkenes

They are open-chain hydrocarbons and have a double bond, whose general formula is Ç_noH_2n.

Alkenes characteristics

• They are also called olefins, alkenes or ethylenic hydrocarbons.
• They are industrially obtained from the cracking of alkanes present in petroleum.
• They are used as raw material in industry: plastics, dyes, explosives, etc.

Examples of alkenes

Alkynes

They are open-chain hydrocarbons with the presence of a double bond, whose general formula is Ç_noH_2n-2.

Alkynes Characteristics

• They are more reactive than alkanes and alkenes due to the triple bond.
• Alkynes with more than 14 carbon atoms are solid.
• The most used alkyne is acetylene, commonly used in the production of synthetic rubbers, textile fibers and plastics.

Examples of alkynes

Alkadienes

They are open-chain hydrocarbons and the presence of two double bonds, whose general formula is Ç_noH_2n-2

Characteristics of alkadienes

• Also called dienes or diolefins
• They are found in nature in terpenes, which are extracted from essential fruit oils.
• The best known compound is isoprene, found in natural rubber and essential oils.

Examples of alkadienes

Cyclans

They are closed-chain hydrocarbons with single bonds between carbon and hydrogen atoms, whose general formula is Ç_noH_2n.

Cyclan Characteristics

• They are also called cycloalkanes or cycloparaffins.
• They are unstable when subjected to high pressure.
• Chains with more than 6 carbons are stable, whereas chains with less than 5 carbons are reactive.

Examples of cyclans

Cycles

They are closed-chain hydrocarbons with the presence of a double bond, whose structural formula is Ç_noH_2n-2.

Characteristics of cyclenes

• They are also called cycloalkenes.
• Compounds of 3 to 5 carbons are unstable.
• They are usually found in natural gas, oil and petroleum.

Examples of cyclenes

cyclists

They are closed-chain hydrocarbons with the presence of a triple bond, whose structural formula is Ç_noH_2n-4.

Cycling Characteristics

• They are also called cycloalkynes or cycloalkynes.
• They are cyclic and unsaturated hydrocarbons.
• They are unstable due to triple bonding and are not found in nature.

Examples of cyclines

Aromatics

They are closed chain hydrocarbons with alternating single and double bonds.

Characteristics of aromatics

• They are also called arenas.
• They are unsaturated compounds, as they have 3 double bonds.
• They consist of at least one aromatic ring.

Examples of aromatics

You may also be interested in:

• Petroleum
• oil refining
• Acetylene

Hydrocarbon Summary

Occupation	General Formula	Features
alkane		Open chain with simple links.
alkene		Open chain with double bond.
alkyne		Open chain with triple bond.
alkadiene		Open chain with two double bonds.
Cyclans		Closed chain with simple connections.
Cycles		Closed chain with double bond.
cyclists		Closed chain with triple link.
Aromatic	Variable	Closed chain with alternating single and double bonds.

Exercises on Hydrocarbons

1. (UEMA) LPG (Liquefied Petroleum Gas), also popularly known as cooking gas, is a fuel non-renewable fossil that can run out overnight if not used with planning and without excess. It is composed, among other gases, of propane C₃H₈, butane C₄H₁₀ and small amounts of propylene C₃H₆ and butene C₄H₈. These organic compounds are classified as hydrocarbons that have similarities and differences between them. Based on the type of bond between carbons and the classification of the carbon chain of the compounds above, it can be stated that:

a) the unsaturated compounds are propane and butane.
b) the unsaturated compounds are propene and butene.
c) the unsaturated compounds are propene and butane.
d) the compounds have homocyclic chains.
e) the compounds have heterocyclic chains.

See Answer

Alternative b) the unsaturated compounds are propene and butene.

a) WRONG. These compounds do not have unsaturations, their bonds are simple.

b) CORRECT. The term "en" indicates the presence of double bonds in the compounds.

c) WRONG. Butane has no unsaturations.

d) WRONG. These chains are closed and the carbon atoms are linked by single bonds.

e) WRONG. These chains have a heteroatom, such as oxygen and nitrogen.

2. (Uel) One of the formula C hydrocarbons₅H₁₂ may have carbon chain:

a) saturated cyclic.
b) heterogeneous acyclic.
c) branched cyclic.
d) unsaturated open.
e) open branched.

See Answer

Alternative e) open branched.

a) WRONG. A saturated cyclic compound corresponds to a cyclan, whose formula is C_noH_2n.

Example:

b) WRONG. A heterogeneous acyclic compound has the presence of another element in addition to the intercalated carbon in the chain.

Example:

c) WRONG. A branched cyclic compound has formula C_noH_2n.

Example:

d) WRONG. An unsaturated open chain compound can be an alkene or an alkyne, the formula of which is respectively C._noH_2n and C_noH_2n-2.

Examples:

e) CORRECT. An open-chain branched compound is an alkane whose formula is C_noH_2n+2. A compound of 5 carbons and 12 hydrogens could be isopentane.

Example:

3. (PUC) Alkynes are hydrocarbons:

a) saturated aliphatics.
b) saturated alicyclics.
c) double bond unsaturated aliphatics.
d) triple bond unsaturated alicyclics.
e) triple-bonded unsaturated aliphatics.

See Answer

Alternative e) triple bond unsaturated aliphatics.

a) WRONG. The open-chain and single-bonded compounds are alkanes.

Example:

b) WRONG. Cyclic compounds with single bonds are cyclans.

Example:

c) WRONG. Open-chain and double-bonded compounds are alkenes.

Example:

d) WRONG. Cyclic and triple-bonded compounds are cyclins.

Example:

e) CORRECT. Alkynes are open-chain and triple-bonded compounds.

Do you want to keep testing your knowledge? Be sure to check out these lists:

• Exercises on Hydrocarbons
• Exercises on Organic Chemistry
• Exercises on Organic Functions