Saturated hydrocarbons with a single covalent bond between hydrogen and carbon atoms are known as alkanes. This means that each atom has a single pair of electrons. Alkanes have the general formula CnH(2n+2). In this article, we will learn about the definition and meaning of alkanes, its properties, nomenclature, and uses.
Alkanes- Definition
Alkanes are a class of organic compounds composed only of carbon and hydrogen atoms, with single bonds between the carbon atoms. They are sometimes referred to as "saturated hydrocarbons" because they contain the maximum number of hydrogen atoms possible for a given number of carbon atoms. They are also called paraffin because alkanes are inert under normal conditions of temperature and pressure and do not react with reagents like acids, bases, oxidizing agents, and reducing agents. However, under drastic conditions, i.e., under high temperatures and pressures, alkanes undergo some reactions. Alkanes are the simplest type of hydrocarbon that have the general molecular formula CnH2n+2, where "n" is the number of carbon atoms in the molecule.
1 Types The alkanes may be divided as:
Acyclic alkanes: They are also known as open-chain alkanes or straight-chain alkanes, are a type of alkane that has a linear or branched carbon chain that is not arranged in a closed ring or cyclic structure. They are saturated hydrocarbons that have only single covalent bonds between the carbon atoms and are fully saturated with hydrogen atoms.
They have a general formula CnH2n+2.
Acyclic alkanes can have various chain lengths and can be either straight or branched, depending on the arrangement of carbon atoms.
Some examples of acyclic alkanes are methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), and pentane (C5H12).
Acyclic alkanes can have different physical and chemical properties, such as boiling and melting points, solubility, density, and reactivity, depending on their molecular size and structure.
Cyclic Alkanes: They are also known as cycloalkanes, are a type of alkane that have a closed ring or cyclic structure made up of carbon and hydrogen atoms. They are saturated hydrocarbons that have only single covalent bonds between the carbon atoms and are fully saturated with hydrogen atoms.
The general formula for cycloalkanes is CnH2n. The simplest cyclic alkane is cyclopropane (C3H6), which consists of a three-carbon ring, while cyclobutane (C4H8), cyclopentane (C5H10), and cyclohexane (C6H12) are examples of cyclic alkanes with four, five, and six carbon atoms in their rings, respectively.
Cyclic alkanes can have various sizes and shapes, and can also contain substituents, such as methyl groups, attached to the ring.
Cyclic alkanes have distinct physical and chemical properties compared to their open-chain counterparts, such as higher melting and boiling points, and different conformations due to ring strain.
They are used in various applications, such as solvents, fuels, and building blocks for organic synthesis. Â
2. Nomenclature of Alkanes
Alkanes have the general formula CnH(2n+2), where n=1,2,3,4,.... The names of alkanes have a suffix- ane, and the prefix depends on the number of carbon atoms, according to the IUPAC system. The following are some saturated hydrocarbon names:
No. of Carbon atoms | Formula | IUPAC name |
1 | CH4 | Methane |
2 | C2H6 | Ethane |
3 | C3H8 | Propane |
4 | C4H10 | Butane |
5 | C5H12 | Pentane |
6 | C6H14 | Hexane |
7 | C7H16 | Heptane |
8 | C8H18 | Octane |
9 | C9H20 | Nonane |
10 | C10H22 | Decane  |
2. Rules The nomenclature Of Alkanes
Follows the rules established by the International Union of Pure and Applied Chemistry (IUPAC). Here are the general steps for naming alkanes:
Find the longest continuous chain of carbon atoms in the molecule, which will give the root name of the alkane. For example, a molecule with five carbon atoms would be named with the root "pentane."
Number the carbon atoms in the chain starting from the end that gives the lowest possible number to substituents.
Identify any substituent groups attached to the carbon chain and name them using prefixes, such as "methyl," "ethyl," "propyl," and so on. The substituent name comes before the root name, and multiple substituents are listed alphabetically.
Use the prefix "iso-" to indicate a branch that is attached to the second carbon of the chain.
Use the prefix "neo-" to indicate a branch that is attached to the third carbon of the chain.
Use the prefix "cyclo-" to indicate that the carbon chain is arranged in a ring.
Combine the names of the substituents and the root name to give the complete name of the compound.
For example, Branched-chain Alkanes:
Cycloalkanes:
cycloalkanes
3. Writing Structural Formula of Alkanes
The structural formula of alkanes can be written by drawing a series of carbon atoms in a row, with each carbon atom forming single bonds with two neighboring carbon atoms and with hydrogen atoms attached to the remaining bonding sites. Here are some examples of the structural formula for alkanes:
Formula | IUPAC Name | Structure |
CH4 | Methane |  |
C2H6 | Ethane |  |
C3H8 | Propane |  |
C4H10 | Butane |  |
C5H12 | Pentane |  Â In larger alkanes, the structural formula can become more complex, with branching or cyclic structures. In these cases, the structural formula must accurately reflect the positions of the carbon atoms and hydrogen atoms in the molecule. |
In larger alkanes, the structural formula can become more complex, with branching or cyclic structures. In these cases, the structural formula must accurately reflect the positions of the carbon atoms and hydrogen atoms in the molecule. For example, The structural formula of- 3- Ethyl-2-methyl pentane is
3,4,4,5-Tetramethylheptane is
structural formula of 3,4,4,5-Tetramethylheptane
4. Isomerism in Alkanes
Isomerism is the phenomenon of having two or more compounds with the same molecular formula but different structural arrangements. Alkanes exhibit different types of isomerism, which include: 4.1 Chain isomerism: This occurs when there are different ways of arranging the carbon atoms in a molecule, resulting in different chain lengths or branching patterns. For example, butane and isobutane both have the molecular formula C4H10 but have different chain arrangements.
4.2 Position isomerism: This occurs when functional groups or substituents are attached to different carbon atoms in a molecule. For example, in the isomers 1-propanol and 2-propanol, the hydroxyl group is attached to different carbon atoms.
Conformational isomerism: This occurs when the same molecule has different spatial arrangements due to the free rotation around single bonds. For example, in the isomers of ethane, the staggered and eclipsed conformations result in different spatial arrangements of the hydrogen atoms.
Conformational isomerism
5. Physical Properties of Alkanes
Here are some of the physical properties of alkanes:
State of Matter: Alkanes with low molecular weight are gases at room temperature, while alkanes with higher molecular weight are liquids or solids. For example, methane (CH4) is a gas at room temperature, while octane (C8H18) is a liquid.
Boiling and Melting Points: Alkanes have relatively low boiling and melting points, which increase with increasing molecular weight. The boiling points and melting points of alkanes increase with the number of carbon atoms in the molecule as the intermolecular forces between molecules become stronger.
Solubility: Alkanes are non-polar in nature, and therefore, they are generally insoluble in water but are soluble in nonpolar solvents such as hexane, benzene, and chloroform.
Density: The density of alkanes increases with increasing molecular weight as the molecule's mass increases.
Color: Alkanes are colorless.
Odor: Alkanes with low molecular weight have a faint, sweet odor, while higher alkanes have little to no odor.
Flammability: Alkanes are highly flammable in air and can form explosive mixtures. The flammability of alkanes increases with decreasing molecular weight.
6. Uses of Alkanes
Alkanes have many important uses in various industries and applications, some of which include:
Fuel: Alkanes are the main components of gasoline, diesel, and aviation fuels. They are also used as fuel for home heating and cooking.
Solvent: Alkanes such as hexane and heptane are used as solvents in various industries, including paint, printing, and pharmaceuticals.
Lubricant: Alkanes such as mineral oil are used as lubricants in machinery to reduce friction and wear.
Plastic Production: Alkanes are used as feedstocks for the production of plastics, such as polyethylene and polypropylene.
Chemical Synthesis: Alkanes are used as starting materials for the synthesis of various chemicals, including alcohols, aldehydes, and acids.
Refrigerant: Some alkanes, such as propane and butane, are used as refrigerants in refrigeration and air conditioning systems.
Cosmetics: Alkanes such as paraffin and petrolatum are used in the production of cosmetics, including creams and lotions.
Agriculture: Alkanes are used as fumigants to control pests and diseases in crops.
Key Takeaways
Alkanes are saturated hydrocarbons, containing one single bond between carbon and carbon ad carbon and hydrogen atoms.
Alkanes can broadly be divided into acyclic and cyclic alkanes.
They are relatively unreactive and are commonly used as fuels, solvents, and lubricants.
Alkanes can be easily identified by their characteristic properties, including high boiling and melting points, low reactivity, and non-polarity.
They are commercially important because they are the primary constituents of gasoline and lubricating oils, and they are widely used in organic chemistry.
FAQs
1. What are alkanes?
Alkanes are a family of organic compounds that consist of only carbon and hydrogen atoms and have single covalent bonds between the carbon atoms. They are also known as saturated hydrocarbons, as they contain the maximum number of hydrogen atoms possible.
2. What is the general formula for alkanes?
The general formula for alkanes is CnH2n+2, where n is the number of carbon atoms in the molecule. This formula applies to all alkanes, regardless of their chain length.
3. How are alkanes named?
Alkanes are named according to the rules of the IUPAC (International Union of Pure and Applied Chemistry) system. The name of an alkane is based on the number of carbon atoms in the molecule and the structure of the carbon chain.
4. What are some common uses of alkanes?
Alkanes have many important uses in various industries and applications, including as fuel, solvents, lubricants, plastic production, chemical synthesis, refrigerants, and cosmetics.
5. What are some physical properties of alkanes?
Physical properties of alkanes include being colorless, odorless, and having relatively low boiling and melting points. They are generally insoluble in water but are soluble in nonpolar solvents such as hexane, benzene, and chloroform.
6. What is isomerism in alkanes?
Isomerism is the phenomenon of having two or more compounds with the same molecular formula but different structural arrangements. Alkanes exhibit different types of isomerism, including chain isomerism, position isomerism, geometric isomerism, and conformational isomerism.
7. What is the relationship between the boiling point and molecular weight of alkanes?
The boiling point of alkanes increases with increasing molecular weight as the intermolecular forces between molecules become stronger.
Conclusion
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