Alkanes - preparing, reactions, physical properties

Alkanes are also introduced as Paraffin compounds. Most fuels such as petrol, diesel, LP gas, kerosene and more are alkanes and burnt with oxygen to get energy. All of those fuels are come through petroleum industry. There are only single bonds between carbon atoms in alkanes. Usually, when we start to learn organic chemistry compounds we start from alkanes. In this tutorial, we will learn physical properties chemical properties and reactions of alkanes.

Physical properties of Alkanes

  • alkanes are saturated hydrocarbons because there are no double or triple bonds between carbon atoms in alkanes.
  • There are only single bonds between carbon atoms ( -C-C-C- ).
  • General formula of alkane is C2H2n+2 ; n = 1,2,3,4...
  • Simple alkanes such as methane, ethane, propane, butane exist as gaseous compounds. When number of carbon atoms is icreased, those alkanes become liquid and sold compounds.

Alkanes IUPAC naming | nomenclature

Alkanes IUPAC naming is simple. We should look about length of carbon chain (number of carbon atoms), substituents, when writing the IUPAC name. Some examples are noted here.

Learn more about alkane IUPAC naming

some IUPAC names of alkanes

alkanes IUPAC names

Preparation of Alkane

Alkanes are prepared from different organic compounds such as unsaturated hydrocarbon (alkenes, alkynes), Alkyl Halides. These different compounds react with different reagents under different conditions to give alkanes.

Preparation of Alkanes by unsaturated Hydrocarbon

Alkenes and Alkynes are unsaturated hydrocarbons. They can be converted into Alkanes by catalytic hydrogenation. Raney Nickle(Ni), Platinum(Pt), or Palladium(Pd) are used as catalysts under higher tempeature..

alkane prepare by alkenes and alkynes

Preparation of Alkanes by alkyl halides

Alkyle Halides :
Halogen(F,Cl,Br,I) derivatives of Alkane compounds
ex: CH3CH2Br     CH3CH2BrCH2I

Wurtz reaction

Alkyl halides are treated with sodium in dry ether. Then a symmetrical alkanes containing twice the number of carbon atoms of alkyl halide is obtained wurtz reaction

Mechanisms of Wurtz reaction>

There are 2 suggested mechanisms for Wurtz Reaction

  1. Through intermediate formation of an organometallic compound
  2. Through formation of intermediate radicals

Reduction of alkyl halides

Alkyle halides (except fluorides) can be reduced to alkanes by suitable reducing agents.

Reactions of alkanes

Halogenation of alkanes

Alkanes react with F2 ,Cl2 , Br2 , I2 under different conditions and give halo alkanes (alkyl halides) as products.

Methane and fluorine reaction

Methane reacts with F2 without sun light too. If sun light exists, explosions are occured.

fluorine and methanw

Methane and chlorine reaction

Methane does not react with Cl2 in dark. When sun light exists, a mixture of chlorinated alkanes is given as products .

chlorine and methane

Methane and bromine reaction

Bromine's reaction with is same as chlorine. Br2 and methane do not react in dark, but reaction occurs in the sun light slowly.

bromine and methane

Methane and iodine reaction

Iodine reacts with methane only if there are catalyst.

iodine and methane

Products of chlorination of methane

A mixture of chlorinated alkanes is given as products. .

products chlorinated of methane
Mechanism of chlorination of alkanes

Sources and uses of alkanes

Methane formation and uses

Methane gas is formed in anaerobic decomposition of plant materials by bacteria. Also methane forms in wetlands. Methane contains in bio gas. Methane gas can be used as a fuel.

In petroleum and crude oil industry

Simple chain alkanes, chain branches alkanes and cyclic alkanes includes in crude oil. Liquid petroleum (LP gas) can be taken from gaseous alkanes by liquidizing by pressurizing. Propane and butane include in liquid petroleum.

Obtain petrol, diesel

Gaseous alkanes are removed from crude oil. Then, that crude oil is distilled to get diesel and petrol.

Examples and problems of alkanes

Problem 1

Draw all possible aliphatic structures for molecular formula C5H12

Different structures of alkanes

There are 5 carbon atoms in this molecule(C5H12). First, we should check whether this is an alkane or alkene or alkyne?. Then we take common formula of alkane CnHn. Substitute n=5, then
C5H2*5 + 2
Now we sure this molecular formula is related to an alkane. Now we can draw all possible aliphatic structures for this molecule.


Are alkanes saturated compounds?


When there are four sigma bonds around carbon atom, that carbon atom is called saturated.

Carbon atoms of alkanes have four sigma bonds around the carbon atom (no pi bonds). Methane, ethane are some saturated alkane compounds.

alkanes saturated compounds