Alkanes

What are Alkanes?

Alkanes are organic compounds that consist of single-bonded carbon and hydrogen atoms. The formula for Alkanes is CnH2n+2, subdivided into three groups – chain alkanes, cycloalkanes, and the branched alkanes.

Alkanes are comprised of a series of compounds that contain carbon and hydrogen atoms with single covalent bonds. This group of compounds consists of carbon and hydrogen atoms with single covalent bonds. Also, comprises of a homologous series having a molecular formula of C nH2n+2.

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Hydrocarbons

The simple alkane methane contains one carbon atom and CH4 as its molecular formula. As this compound have just single covalent bonds only, therefore, its structural formula is

Alkanes

In a long chain alkane molecule, additional carbon atoms are attached to each other with the help of a single covalent bond. Each atom is attached to the sufficient hydrogen atoms to develop a total of four single covalent bonds. This long-chain structure is known as octane. An eight-carbon alkane has a molecular formula – C 8H 18 and structural formula-

Alkanes

Alkanes List

The list of some Alkanes and the molecular formula is given below.

List of Alkanes  Molecular Formula  Structure
Methane (CH4)
Methane

Methane

Ethane (C2H6)
Ethane

Ethane

Propane (C3H8)
Propane

Propane

Butane (C4H10)
Butane

Butane

Pentane (C5H12)
Pentane

Pentane

Hexane (C6H14)
Hexane

Hexane

Heptane (C7H16)
Heptane

Heptane

Octane (C8H18)
Octane

Octane

Nonane (C9H20)
Nonane

Nonane

Decane (C10H22)
Decane

Decane

Physical Properties of Alkanes

1. The Solubility of Alkanes

  • Due to very little difference of electronegativity between carbon and hydrogen and covalent nature of C-C bond or C-H bond, alkanes are generally non-polar molecules.
  • As we generally observe, polar molecules are soluble in polar solvents whereas non-polar molecules are soluble in non-polar solvents. Hence, alkanes are hydrophobic in nature that is, alkanes are insoluble in water.
  • However, they are soluble in organic solvents as the energy required to overcome the existing Van Der Waals forces and generate new Van Der Waals forces is quite comparable.

2. The Boiling Point of Alkanes

  • As the intermolecular Van Der Waals forces increase with the increase of the molecular size or the surface area of the molecule we observe:
  • The boiling point of alkanes increases with increasing molecular weight,
  • The straight-chain alkanes are observed to have a higher boiling point in comparison to their structural isomers.

3. The Melting Point of Alkanes

  • The melting point of alkanes follow the same trend as their boiling point that is, it increases with increase in molecular weight.
  • This is attributed to the fact that higher alkanes are solids and it’s difficult to overcome intermolecular forces of attraction between them.
  • It is generally observed that even-numbered alkanes have a higher trend in melting point in comparison to odd-numbered alkanes as the even-numbered alkanes pack well in the solid phase, forming a well-organized structure which is difficult to break.

Alkyl Groups

When a substituent like halogen bonds to an alkane molecule, one carbon-hydrogen bond of the molecule gets converted to carbon-substituent bond. It can be understood with an example- A new compound known as chloromethane is formed when methane reacts with chlorine. The new compound is composed of a CH3 group that is bonded to a chlorine atom.

Alkyl Groups

When an alkane having hydrogen is removed from one bond, it is called an alkyl group. This Alkyl group is often denoted by the letter R same as halogens represent by the letter X. Here is a methane‐chlorine reaction that can be generalized as

Alkyl Groups

FAQs

1. What are the first four alkanes?

Ans: Methane (CH4), ethane (C2H6), propane (C3H8) and butane (C4H10) are the first four alkanes. Methane gas, whose molecular formula is CH4, is the simplest alkane.

2. How are alkanes classified?

Ans: Alkanes are single-bond hydrocarbon atoms. Three types of alkanes are available: linear straight alkanes branched alkanes and cyclic alkanes.

3. Is alkane a functional group?

Ans: Usually, alkanes are not considered functional groups; rather, an alkane is a compound that lacks functional groups. A carbon-carbon double bond is a functional group in an alkene.

4. What is the general formula of alkyne?

Ans: In a homologous series, alkynes are compounds with the general molecular formula of CnH2n‐2.

5. What is the simplest alkyne?

Ans: Alkynes are triple-bond carbon-carbon hydrocarbons. They do not display any geometric or optical isomerism. Ethyne (HC-CH), frequently known as acetylene, is the easiest alkyne as shown on the right.

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