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Aliphatic has been derived from the Greek word ‘Aleiphar’ which translates to ‘fat’. This is used to define hydrocarbons that have been obtained by the chemical degradation of fats or oils. Organic compounds having carbon and hydrogen linked together in straight chains such compounds are known as aliphatic compounds or aliphatic hydrocarbons.
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Keyterms: Organic compounds, Carbon, Hydrogen, Hydrocarbon, Covalent bonds, Double bond, Triple bond, Cycloalkane, Cycloalkenes, Cycloalkynes
Aliphatic Hydrocarbons
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Those compounds which are made up of two elements: carbon and hydrogen are known as hydrocarbons. These are the simplest organic compounds that have been divided into two categories: aliphatic hydrocarbons and aromatic hydrocarbons. Organic compounds having carbon and hydrogen linked together in straight chains such compounds are known as aliphatic compounds or aliphatic hydrocarbons.
It happens that the chain formed sometimes is branched or in the form of non-aromatic structures. Notably when other elements like nitrogen, chlorine, oxygen and sulphur are linked with carbon atoms in the chain.There are three types of Aliphatic hydrocarbons. All three types have been given below.
- Alkanes: aliphatic hydrocarbons with single covalent bonds.
- Alkenes: aliphatic hydrocarbons with at least one C-C double bond.
- Alkynes: aliphatic hydrocarbons with at least a C-C triple bond.
Those aliphatic hydrocarbons with a ring of C atoms are called cycloalkanes or cycloalkenes or cycloalkynes.
Properties of Aliphatic Hydrocarbons
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Some of the properties of Aliphatic Hydrocarbons have been given below.
- Usually, aliphatic hydrocarbons are flammable. Therefore, they can be used as fuels.
- Aliphatic compounds can be acyclic or cyclic. They can either contain rings of carbon atoms in their molecule or can be in the form of a close chain.
- Boiling Point and Melting Point: the minor difference between the electronegativities of hydrogen and carbon means that the bond between both of them is only weakly polar. If two alkanes having the same molecular weights are there then the highly branched one will have the lower boiling point. The melting point of aliphatic hydrocarbons increases with size but in a less regular manner.
- Hydrocarbons are nonpolar therefore they tend to be insoluble in polar solvents and water. They are most likely to be dissolved in non-polar solvents such as benzene and diethyl ether. Hydrocarbons can be called hydrophobic or lipophilic.
- Hydrocarbons are less dense when compared to water which means they tend to float on the surface of the water.
Read More:
| Related Concepts | ||
|---|---|---|
| Hypochlorous Acid | Hexane | Birch Reduction Mechanism |
| Benzene | Saturated Hydrocarbons | Cracking |
Examples of Aliphatic Hydrocarbons
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A list of Aliphatic Hydrocarbons is given below:
| Number of carbon atoms | Aliphatic Hydrocarbons |
|---|---|
| 1 | Methane |
| 2 | Ethane, Ethene, Ethyne |
| 3 | Propane, Propene, Propyne, cyclopropane |
| 4 | Methylpropane, butane, cyclobutene |
| 5 | Cyclopentene, pentane, dimethylpropane |
| 6 | Hexane, cyclohexene, cyclohexane |
| 7 | Cycloheptane, cycloheptene, heptane |
| 8 | Octane, cyclooctane, cyclooctene |
Saturated and Unsaturated Hydrocarbons
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- Aliphatic hydrocarbons have been divided into two categories: saturated or unsaturated.
- The saturated hydrocarbons are normally alkanes which are open-chain hydrocarbons having C-C single bonds.
- The basic nature of such compounds is that they are inert and do not quickly react with acid, basis, or other reagents.
- The unsaturated hydrocarbons are those which have at least one double bond. In such hydrocarbons, more hydrogen atoms can be added to these molecules. As compared to the saturated ones such molecules are readily reactive. The double bond is less than twice as strong as a single bond. Due to this one part of a double bond can be broken very easily apart than it would be to break a single bond.
- In the saturated hydrocarbons, no more hydrogen atoms can be added. Unsaturated hydrocarbons are normally alkenes or alkynes which have carbon-carbon double bond and triple bond.
Diagram showing the structure of saturated and unsaturated hydrocarbons:
Read More:
| Related Concepts | ||
|---|---|---|
| Anthracene | Michael Addition Mechanism | Electrophilic Substitution of Benzene |
| Addition Reaction of Alkyne | Octane Formula | Conformers |
IUPAC Nomenclature
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The International Union of Pure and Applied Chemistry (IUPAC) has a method of naming hydrocarbons and other organic compounds. This method is called the IUPAC system of Nomenclature. Below is given the stem name and also the number of carbon atoms attached to the longest continuous chain.
| Stem | Number of C-atoms |
|---|---|
| meth- | 1 |
| eth- | 2 |
| prop- | 3 |
| But- | 4 |
| pent- | 5 |
| hex- | 6 |
| hept- | 7 |
| oct- | 8 |
| non- | 9 |
| dec- | 10 |
Extraction of Aliphatic Hydrocarbons
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Pressurized Fluid Extraction is the method used for the extraction of Aliphatic Hydrocarbons. Under PFE aqueous extraction solvents are used which are also organic. Water that has been extracted from hot steam can also be used for the extraction of aliphatic hydrocarbons from solid and semi-solid environmental samples.
Also Read:
| Related Articles | ||
|---|---|---|
| Polymerisation | Lindlar Catalyst | Conformational isomers |
| Cycloalkanes | Conformation | Huckel Rule of Aromaticity |
| Unsaturated Hydrocarbons | Electrophilic Substitution Reactions | Alkanes |
Points To Remember
- When the organic compounds having carbon and hydrogen are linked together in straight chains such compounds are known as aliphatic compounds or aliphatic hydrocarbons.
- Aliphatic hydrocarbons have been divided into two categories: saturated or unsaturated. The saturated hydrocarbons are normally alkanes which are open-chain hydrocarbons having C-C single bonds.
- The unsaturated hydrocarbons are those which have at least one double bond. In such hydrocarbons, more hydrogen atoms can be added to these molecules.
- Pressurized Fluid Extraction is the method used for the extraction of Aliphatic Hydrocarbons.
- Aliphatic compounds can be acyclic or cyclic. They can either contain rings of carbon atoms in their molecule or can be in the form of a close chain.
Previous Year Questions
- Variable oxidation state and degenerated orbital shows: [BCECE 2004]
- The decreasing order of electron affinity is: [UPSEE 2016]
- Atomic radius (pm) of….[TS EAMCET 2017]
- What does the electronic configuration…..[GUJCET 2010]
- As we move from left to right in the 3d-series elements [COMEDK UGET 2011]
- Atomic numbers of vanadium, chromium, nickel and iron are [COMEDK UGET 2014]
- Which one of the following is the least electropositive element? [COMEDK UGET 2007]
- The electronegativity of the following elements is in the order
- The conversion of n-hexane to benzene, in the presence of chromic acid, is called? [JEE 2003]
- Some meta-directing substituents in aromatic substitution are given. Which one is most deactivating? [NEET 2013]
- The effective electrophile in aromatic sulphonation is? [MU OET 2010]
- Which of the following compounds undergo nitration more readily? [AMUEEE 2014]
- Which of the following reagents will be able to distinguish between 1-butyne and 2-butyne?... [NEET 1980]
- A compound is treated with NaNH2 to give sodium salt. Identify the compound... [NEET 1993]
- Acetylenic hydrogens are acidic because... [NEET 1989]
- In Friedel-Craft's synthesis of toluene, the reactants in addition to anhydrous AlCl3 are... [NEET 2000]
- In Friedel-Craft's alkylation besides AlCl3 the other reactants are... [NEET 1999]
- Liquid hydrocarbons can be converted to a mixture of gaseous hydrocarbons by… [NEET 2010]
Sample Questions
Ques. What are the applications of aliphatic hydrocarbons? (1 mark)
Ans. Aliphatic hydrocarbons are flammable usually, we can use them as fuel like methane in Bunsen burners, ethylene (acetylene) in welding, liquified natural gas (LNG), etc.
Ques. Name the 4 types of hydrocarbons? (1 mark)
Ans. Hydrocarbons are made up of hydrogen and carbon. There are four groups of hydrocarbons and these are alkanes, alkenes, aromatic, and alkynes.
Ques. What are the effects of hydrocarbons? (1 mark)
Ans. Hydrocarbons as major components of oil, natural gas, and pesticides deplete ozone and lead to climate change and the greenhouse effect.
Ques. Are aliphatic hydrocarbons considered harmful? (1 mark)
Ans. Aliphatic hydrocarbons tend to crack when heated and create toxic gases like phosgene and hydrogen chloride. These gases are dangerous for the lungs and heart. The effect of respiratory function adversely.
Ques. Is alcohol an aliphatic compound? (1 mark)
Ans. Aliphatic compounds such as hexane are not made up of hydrogen and carbon. They can also have oxygen-like atoms. Isopropanol contains a group of alcohol (OH) bound to an aliphatic carbon chain.
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