Aliphatic Hydrocarbons

What are Aliphatic Hydrocarbons

In organic chemistry, hydrocarbons refer to compounds consisting of nothing but carbon and hydrogen. Further, the hydrocarbons get classified into two broad categories - aliphatic hydrocarbons and aromatic hydrocarbons. The term aliphatic comes from the Greek word ‘Aleiphar,’ which means ‘fat.’ It refers to hydrocarbons obtained by the chemical degradation of oils or fats. An aliphatic compound is an organic one. It has carbon and hydrogen joined together in straight, branched chains, or non-aromatic rings. These compounds may be both saturated (alkanes) and unsaturated (alkenes, alkynes). Most simple aliphatic hydrocarbon is methane, CH4. A majority of aliphatic hydrocarbons are flammable. Ethylene, isooctane, and acetylene are examples of the same. In this article, you can learn about aliphatic hydrocarbons, saturated and unsaturated hydrocarbons, and their properties, etc.   


What is Aliphatic Compound?

An aliphatic compound or aliphatic hydrocarbon contains hydrogen and carbon atoms linked together in straight chains. Sometimes, the chains can also occur in branched form or non-aromatic structures. Keep in mind that aliphatic compounds are organic. Apart from the hydrogen, different elements like oxygen, nitrogen, chlorine, and sulfur may get joined with the carbon atoms in the chain. 


Halogenated aliphatic hydrocarbons are chemicals where one or more hydrogen atoms get replaced by the halogen. Aliphatic hydrocarbons encompass a diverse group of organic compounds characterized by different single, double, and triple bonds, and an open-chain structure as well. Below is a classification of hydrocarbons; as you can see, there are four types of aliphatic compounds. They are alkanes, alkenes, alkynes, and cyclic or cyclo-alkanes. 


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Properties of Aliphatic Hydrocarbons

  • A great majority of aliphatic compounds are flammable. They often get used as fuel sources like methane, propane, ethylene, acetylene, and so on. 

  • Aliphatic compounds may be cyclic or acyclic. They can have close chains or rings of carbon atoms in their molecule.   

  • When two alkanes have equal molecular mass, the more highly branched alkane has a lower boiling point. The melting points for aliphatic compounds increase with size, but in a less typical manner. 

  • Since the hydrocarbons are nonpolar, they are insoluble in water and other polar solvents. However, they get dissolved in non-polar solvents like benzene and diethyl ether. Also, note that hydrocarbons are less dense than water, and they can stay afloat in water surfaces.

Below you can Find Some Examples and a List of Aliphatic Hydrocarbons

No. of Carbon Atoms

Names of Aliphatic Hydrocarbons

1

Methane

2

Ethane, Ethene, Ethyne

3

Propane, Propene, Propyne, Cyclopropane

4

Methylpropane, Butane, Cyclobutane

5

Cyclopentene, Pentane, Dimethylpropane

6

Hexane, Cyclohexane, Cyclohexene 

7

Heptane, Cycloheptane, Cycloheptene

8

Octane, Cyclooctane, Cyclooctene

 

Extraction of Aliphatic Hydrocarbons

Aliphatic compounds get extracted by the process of pressurized fluid extraction (PEE). Organic and aqueous extraction solvents get used in the process of PEE. Water, when converted to steam, can get used to obtaining aliphatic hydrocarbons from solid and semi-solid environmental samples. There has been a minimal usage of aliphatic hydrocarbons as solvents in conventional flame spectrometry. Occasionally, they get used as diluents for other solvents. 


Saturated and Unsaturated Hydrocarbons

Aliphatic compounds can be either saturated or unsaturated. Saturated hydrocarbons mostly contain alkanes. They are open-chain hydrocarbons having carbon-carbon single bonds. Mostly, the bond refers to a covalent bond. Such compounds are inert, and they don’t quickly react with acid, bases, or various reagents. When hydrocarbon molecules don’t have any double bonds in them, it becomes saturated hydrocarbons. 


When the hydrocarbon molecules have at least one double bond, you can call them unsaturated. It means those molecules can accept more hydrogen atoms. These hydrocarbons are more reactive than saturated ones because the double bonds are not as strong as single bonds in saturated hydrocarbons. One part of the double bond is easily breakable as compared to breaking an entire single bond. 


In saturated hydrocarbons, there are no double bonds. It means that there are adequate hydrogen atoms in the molecule and it has no space for adding more. In unsaturated hydrocarbons, you can see a fewer amount of hydrogen atoms bonding with carbon atoms. Unsaturated hydrocarbons are alkenes and alkynes. They respectively have one C – C double bond and one C – C triple bond.

FAQ (Frequently Asked Questions)

Question 1: Is Heptane Saturated or Unsaturated?

Answer: Before we discuss heptanes, you should know the difference between saturated and unsaturated hydrocarbons. Saturated hydrocarbons are those who get connected by a single covalent bond. Unsaturated hydrocarbons refer to those who get connected by a double or triple bond. Alkanes belong to a saturated group of hydrocarbons, whereas alkenes and alkynes belong to the unsaturated group of hydrocarbons. Here, the heptane is an alkane, and its molecular formula is C₇H₁₆. Below is the structure of heptane.

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As you can see that heptane contains only C – C single bonds, it qualifies as a saturated hydrocarbon. Therefore, you can call heptane as a saturated hydrocarbon.

Question 2: What are the Different Types of Hydrocarbons?

Answer: Hydrocarbons are organic compounds that contain nothing but hydrogen and carbon. There are three types of hydrocarbons, namely, saturated, unsaturated, and aromatic hydrocarbons. 

  • Saturated hydrocarbons have single C – C bonds and they are called alkanes. The general formula for an alkane is CₙH₂ₙ₊₂.

  • Unsaturated hydrocarbons have double or triple bonds (C = C or C ≡ C) between carbon atoms. The double-bonded compounds are alkenes, having a general formula CₙH₂ₙ. And the triple-bonded ones are alkynes with a general formula CₙH₂ₙ₋₂.  

  • Aromatic hydrocarbons refer to those containing at least one aromatic ring. It also gets called as arenes.